Biomedical subjects

A E Calogero

Publications and source records attributed to A E Calogero.

At least 73 records · Page 4Linked to original sources

PubMed1994

Effects of local anesthetics on experiential, physiologic and endocrine measures in healthy humans and on rat hypothalamic corticotropin-releasing hormone release in vitro: clinical and psychobiologic implications.

Local anesthetics, given i.v. to treat cardiac arrhythmias and for regional anesthesia, exert prominent central nervous system side effects, such as sensory distortions and mood changes. In experimental animals, these drugs activate limbic structures, such as the amygdala, that may coordinately regulate sensory processing, mood and pituitary hormone secretion during stress. Clinically relevant i.v. doses of the short-acting local anesthetic procaine were administered to 17 healthy volunteers and topographic electroencephalographic (EEG) spectra, stress-responsive neuroendocrine and cardiovascular parameters and sensory-cognitive and mood changes were examined. Because corticotropin-releasing hormone (CRH) mimics the behavioral and physiologic responses to stress and activates limbic structures in experimental animals, the effects of procaine and lidocaine on immunoreactive CRH release from rat hypothalami in vitro were also explored. Procaine administration produced a dose-related increase in fast (21-50 Hz) EEG activity, a significant decrease in alpha EEG activity and dose-dependent increases in heart rate, systolic blood pressure and plasma adrenocorticotropic hormone, cortisol and prolactin secretion. Dose-dependent increases in sensory distortions involved virtually all modalities, particularly auditory, visual and somatosensory. Mood changes occurred in most subjects, including anxiety, euphoria and arousal. In vitro, procaine and lidocaine both produced significant dose-related increases in immunoreactive CRH release from rat hypothalami, maximal at 10(-6) M, that were blocked by carbamazepine, a limbic anticonvulsant used in the management of mood disorders. The electrophysiologic effects of procaine in these volunteers were analogous to local anesthetic effects in experimental animals and consistent with the activation of subcortical structures localized within the temporal lobe, such as the amygdala. The effects of procaine on stress-responsive neurohormones were similar to those of amygdala stimulation both in experimental animals and human subjects. The in vitro data suggested that procaine-induced pituitary-adrenal activation involves stimulation of hypothalamic CRH, although additional (e.g., limbic-hypothalamic) mechanisms may contribute in vivo. These data were compatible with a direct action of local anesthetics on limbic structures that might account for many of the central effects seen with the systemic use of these agents in clinical practice.

Adrenocorticotropic Hormone↗

PubMed1993

Effects of rat prolactin on gonadotropin-releasing hormone secretion by the explanted male rat hypothalamus.

Chronic hyperprolactinemia in the rat is associated with suppression of plasma gonadotropin concentrations. The reduction of gonadotropins is considered to be due to either an inhibitory effect of prolactin (PRL) on pituitary gonadotropin secretion and/or suppression of hypothalamic gonadotropin-releasing hormone (GnRH) release. In contrast to the in vivo effects of PRL on hypothalamic GnRH release, it has recently been reported that endogenous hypothalamic PRL exerts a tonic stimulatory effect on GnRH release in vitro. The present study was undertaken to further evaluate the role of PRL on GnRH release. To accomplish this, we set up a static hypothalamic organ culture system which enabled us to evaluate immunoreactive GnRH (iGnRH) release by individually incubated longitudinally halved hypothalami. PRL at the concentrations of 100 and 1,000 nM (2,300 and 23,000 ng/ml) inhibited iGnRH release. This suppressive effect of PRL was apparently specific since growth hormone, a PRL-related molecule, did not have any significant effect on iGnRH release at the concentration of 1,000 nM (21,500 ng/ml) and a PRL antiserum completely suppressed the inhibitory effect of exogenously added PRL. On the other hand, this antiserum had no effect on basal iGnRH release suggesting that hypothalamic PRL does not regulate GnRH release. Based on the observation that PRL exerts a sexually dimorphic effect on plasma gonadotropin levels, we also evaluated the effects of testosterone (T), dihydrotestosterone (DHT), 17 beta-estradiol (E2), and progesterone (P) on PRL-inhibited iGnRH release in vitro. T, DHT and E2 did not have any detectable effect on PRL-suppressed iGnRH release whereas P, at the concentration of 0.1 nM (0.03 ng/ml), completely abolished the effect of PRL.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Effects of cholecystokinin octapeptide on the hypothalamic-pituitary-adrenal axis function and on vasopressin, prolactin and growth hormone release in humans.

Cholecystokinin (CCK), a gastrointestinal (GI) hormone, is also present in structures of the central nervous system such as cortex, hippocampus, amygdala, olfactory tubercle and in regions involved in the regulation of the pituitary function. Although a number of studies have evaluated the effects of CCK on hypothalamic-pituitary-adrenal (HPA) axis function and on arginine vasopressin (AVP), prolactin (PRL) and growth hormone (GH) plasma levels in the laboratory animal, its role in humans has not been explored. Hence, we examined the effects of the exogenous administration of this GI hormone on corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), cortisol, AVP, PRL and GH plasma levels in humans. To accomplish this, graded doses (0, 50, 140 and 420 ng/kg) of sulfated CCK octapeptide (CCK-8), the full biologically active peptide, were infused intravenously to healthy men in 30 min. Blood samples were collected 30 min and immediately before the infusion was started (baseline) and 15, 30, 45, 60 and 90 min thereafter. CRH, ACTH, and AVP were extracted from plasma proteins using cartridges of SepPak C18. These hormones and cortisol were measured by radioimmunoassay whereas PRL and GH were measured by immunoradiometric assay. CCK-8 increased plasma ACTH and cortisol levels only at the dose of 420 ng/kg, whereas it had no detectable effect on plasma CRH levels. It increased also plasma AVP levels at the doses of 140 and 420 ng/kg. However, this effect reached the statistical significance only at the highest dose tested. CCK-8 stimulated PRL and GH release in a dose-dependent fashion. The lowest stimulatory dose was 140 ng/kg for both hormones.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1993

Effect of selective serotonin agonists on basal, corticotrophin-releasing hormone- and vasopressin-induced ACTH release in vitro from rat pituitary cells.

The present study was undertaken to evaluate the serotonin (5-HT) receptor subtype(s) by which 5-HT acts on the pituitary to stimulate ACTH secretion. We tested the effects of the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), the 5-HT1C receptor agonist metachloro-phenylpiperazine (m-CPP), which also binds to other 5-HT receptors with lower affinity, and the 5-HT2/1C receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) on basal, corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP)-stimulated ACTH release from primary rat anterior pituitary cell cultures. 5-HT, 8-OH-DPAT and DOI significantly increased basal ACTH release, an effect which was antagonized by 5-HT receptor antagonists. 5-HT and DOI were effective at nanomolar concentrations whereas 8-OH-DPAT was effective at higher concentrations. 5-HT, 8-OH-DPAT (both at 10 nmol/l) and DOI (at higher concentrations) blunted the stimulatory effect of CRH. The suppressive effects of 8-OH-DPAT and DOI on CRH-stimulated ACTH release were antagonized by (-)propranolol, a beta-adrenergic receptor antagonist which binds the 5-HT1A receptor with elevated affinity, and ketanserin, a 5-HT2 receptor antagonist respectively. 5-HT, 8-OH-DPAT and DOI showed additive stimulatory effects with AVP but only at the highest concentration tested, whereas m-CPP potentiated AVP-induced ACTH release at concentrations of 1 nmol/l or more. This effect was antagonized by metergoline, a non-selective 5-HT receptor antagonist and mianserin, an antagonist which binds the 5-HT1C receptor with elevated affinity.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1992

Corticotropin releasing hormone related behavioral and neuroendocrine responses to stress in Lewis and Fischer rats.

We have recently shown that susceptibility to streptococcal cell wall (SCW)-induced arthritis in Lewis (LEW/N) rats is related to a lack of glucocorticoid restraint of inflammation while the relative SCW arthritis resistance in histocompatible Fischer (F344/N) rats is related to their greater hypothalamic-pituitary-adrenal (HPA) axis response. The difference in pituitary-adrenal responsiveness results from decreased inflammatory mediator-induced hypothalamic corticotropin-releasing hormone (CRH) biosynthesis and secretion in LEW/N rats. Because CRH not only activates the pituitary-adrenal axis, but also is associated with behavioral responses that are adaptive during stressful situations, we wished to determine if the differential LEW/N and F344/N CRH responsiveness to inflammatory mediators could also be associated with differences in neuroendocrine and behavioral responses to physical and emotional stressors. In this study, LEW/N rats exhibited significant differences compared to F344/N rats, in plasma adrenocorticotropin hormone (ACTH) and corticosterone responses during exposure to an open field, swim stress, restraint or ether. Furthermore, hypothalamic paraventricular CRH mRNA expression was also significantly lower in LEW/N compared to F344/N rats after restraint. These differences in neuroendocrine responses were associated with differences in behavioral responses in LEW/N compared to F344/N rats in the open field. Outbred HSD rats, which have intermediate and overlapping arthritis susceptibility compared to LEW/N and F344/N rats, exhibited intermediate and overlapping plasma corticosterone and behavioral responses to stressful stimuli compared to the two inbred strains. These data suggest that the differences in CRH responses in these strains may contribute to the behavioral and neuroendocrine differences we have observed. Therefore these strains may provide a useful animal model for studying the relationship between behavior, neuroendocrine and inflammatory responses.

Adrenocorticotropic Hormone↗

PubMed1992

Effect of various neurotransmitters and neuropeptides on the release of corticotropin-releasing hormone from the rat cortex in vitro.

Corticotropin-releasing hormone (CRH), in addition to its neuroendocrine role, may act as a central neurotransmitter. Cerebral cortical CRH may have an important role in behavioral and neurodegenerative disorders. To gain an understanding of factors that may influence cortical CRH, we investigated the effect of several neurotransmitters and neuropeptides on the release of immunoreactive CRH (iCRH) from various cerebral cortical regions [frontal (FC), parietal (PC), temporal (TC), and occipital (OC)] in vitro. The hypothalamic release of iCRH was also evaluated under the same experimental conditions. Basal release of iCRH was approximately 2-fold, and KCl-stimulated iCRH release was approximately 4-fold higher in the hypothalamus than in any of the cortical regions. Cortical iCRH release was stimulated by 10 nM somatostatin (SRIF) in PC and 1 nM neuropeptide Y (NPY) in TC. Cortical iCRH release was inhibited by 1 and 10 nM acetylcholine (ACh), 0.1 microM glutamate, and 10 nM NPY. These effects were confined to the FC and/or PC. Hypothalamic iCRH release was stimulated by 1 and 10 nM ACh, 10 microM GABA, and 1 and 10 nM serotonin but was inhibited by 10 nM SRIF and 1 microM GABA. Growth hormone-releasing hormone did not affect cortical or hypothalamic iCRH release. These results demonstrate that CRH release from the cerebral cortex and the hypothalamus are under different regulatory mechanism(s). Furthermore, they indicate that the release of CRH in various cortical regions may be regulated differentially by the same neurotransmitter.

Animals↗

PubMed1992

Limited clinical usefulness of plasma corticotropin-releasing hormone, adrenocorticotropin and beta-endorphin measurements as markers of lung cancer.

We measured plasma corticotropin-releasing hormone (CRH), ACTH, beta-endorphin (beta-EP), and cortisol levels as possible tumor markers in a sequence of 103, randomly selected, patients with lung cancer but without the ectopic Cushing's syndrome and in 72 age- and sex-matched controls. Plasma CRH levels of cancer patients were similar to those of controls both in patients sampled in the morning or in the afternoon. On the other hand, plasma ACTH levels of cancer patients were significantly higher than control patients both in the morning and in the afternoon and showed a preserved circadian rhythm. However, about 35% of cancer patients sampled in the morning and about 60% of those sampled in the afternoon had ACTH levels within the 95% confidence interval (CI) of controls. Also plasma beta-EP levels were more elevated in cancer patients than controls in the morning but about 33% of them and about 80% of those sampled in the afternoon had beta-EP levels within the 95% CI of controls. Despite the higher plasma ACTH levels, cancer patients had cortisol plasma levels similar to controls with preserved circadian rhythm. In conclusion, although mean plasma ACTH and beta-EP were higher in patients affected by lung cancer, their measurements, as well as those of CRH, have practically no diagnostic value. Perhaps measurement of ACTH levels in the bronchial lavage may be more helpful.

Adrenocorticotropic Hormone↗

PubMed1992

Pulsatile activation of the hypothalamic-pituitary-adrenal axis during major surgery.

To examine the response of the hypothalamic-pituitary-adrenal (HPA) axis to severe surgical stress, we measured the immunoreactive plasma levels of corticotropin-releasing hormone (CRH), corticotropin, cortisol, arginine-vasopressin (AVP), atrial natriuretic factor (ANF), neuropeptide Y (NPY), interleukin-1 (IL-1), IL-6, interferon gamma (INF), and tumor necrosis factor-alpha (TNF-alpha) in eight patients with Zollinger-Ellison syndrome (ZES) or mediastinal parathyroid carcinoma, all undergoing major surgery with a standardized anesthetic technique. Blood samples were drawn the morning before surgery, every 10 to 30 minutes throughout surgery (average, 308.7 +/- 15 minutes), and every morning for the next 4 postoperative days (POD). During surgery, plasma CRH concentrations were slightly but not significantly elevated compared with those before surgery and with those of the next 4 POD. However, the values were within the normal range (less than 2.2 pmol/L) and showed 8.9 +/- 0.6 pulses (one pulse every 34.7 +/- 1.6 minutes). Plasma corticotropin, on the other hand, was quite elevated, but was also released in a pulsatile fashion during the surgical procedure (one pulse every 36.7 +/- 1.6 minutes). Most of these secretory episodes of corticotropin were temporally related to those of CRH. Corticotropin returned to basal levels on the first POD and remained so for all 4 POD. Plasma cortisol concentrations increased steadily during surgery and remained elevated the first POD. Cortisol showed 6.2 +/- 1.1 pulses during the operative sampling period (one pulse every 71.8 +/- 13 minutes). Plasma AVP concentrations were also markedly elevated during surgery, but individual secretory pulses were not detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytokines↗

PubMed1992

Therapy with human chorionic gonadotrophin alone induces spermatogenesis in men with isolated hypogonadotrophic hypogonadism--long-term follow-up.

The effects of long-term (14-120 months) hCG-treatment of 17 male patients affected by isolated hypogonadotrophic hypogonadism (IHH) on testicular volume, plasma testosterone levels, and sperm concentration were assessed. Mean testicular volume increased from 3.8 +/- 0.2 (Mean +/- SEM) ml to a maximal of 14.9 +/- 1.1 ml after 22.2 +/- 2.3 months of hCG treatment. Maximal testicular volume correlated positively with the volume recorded before the patients had undergone any previous treatment. Testicular growth was also analysed by sorting the patients into two sub-groups according to whether their initial testicular volume was less than 4 ml (small testis subset, STS) or greater than or equal to 4 ml (large testis subset, LTS), supposedly indicating complete or partial gonadotrophin deficiency, respectively. Testicular volumes in the LTS group were always greater than those of the STS. Plasma testosterone levels reached adulthood values during hCG treatment and no statistically significant difference was detected between LTS and STS patients with IHH. Thirteen patients (70%) became sperm-positive during treatment with hCG alone; five out of eight (60%) were STS patients and eight out of nine (90%) were LTS. In addition, LTS patients always had a greater sperm output than did STS patients. Sperm concentration correlated positively with maximal testicular volume, but not with patient age, length of treatment, or initial testicular volume. The administration of hMG to eight of these patients caused an increase in testicular volume in two patients but the mean volume was not statistically different from that recorded at the end of treatment with hCG alone. Similarly, sperm concentration improved in three patients but again it did not differ significantly from that achieved in the course of hCG treatment. It is noteworthy that one patient became sperm-positive after the addition of hMG to his therapeutic regimen. Among sperm-positive patients attempting conception, seven out of 10 succeeded, two of whom were from the STS group. In summary, this study indicates that hCG alone is an effective treatment to induce complete spermiogenesis in IHH patients regardless of their initial testicular volume. However, a number of IHH patients may benefit from the addition of hMG in terms of testicular volume, sperm output, and pregnancy outcome.

Adolescent↗

PubMed1992

Neurotransmitter-induced hypothalamic-pituitary-adrenal axis responsiveness is defective in inflammatory disease-susceptible Lewis rats: in vivo and in vitro studies suggesting globally defective hypothalamic secretion of corticotropin-releasing hormone.

The susceptibility of female Lewis (LEW/N) rats to the development of streptococcal cell wall (SCW)-induced arthritis and other autoimmune phenomena is associated with the inability of their hypothalamic-pituitary-adrenal (HPA) axis to adequately respond to inflammatory stimuli. In contrast, resistance to the development of SCW-induced arthritis and other inflammatory autoimmune manifestations in histocompatible female Fischer rats (F344/N) is related to their intact HPA axis response to inflammatory mediators. To evaluate the mechanism and the specificity of the HPA axis defect in LEW/N rats, we examined the ability of three major excitatory neurotransmitter systems to activate the HPA axis in both Lewis and Fisher rats. The responsiveness of plasma ACTH and corticosterone to the cholinergic muscarinic receptor agonist arecoline, the alpha 1-adrenergic receptor agonist methoxamine and the serotonin (5-HT) type 2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)2-aminopropane were significantly blunted and/or abolished in LEW/N compared to F344/N rats. To localize the HPA axis defect to the hypothalamic CRH neuron, we evaluated the ability of explanted hypothalami from the two strains to secrete immunoreactive CRH in vitro, in response to acetylcholine (ACh), norepinephrine (NE), 5-HT and the 5-HT agonist quipazine. LEW/N hypothalami released less immunoreactive CRH (iCRH) in response to ACh, NE, 5-HT and quipazine than F344/N hypothalami. The dose-response curves of these compounds in the former were shifted to the right and/or abolished, suggesting decreased sensitivity of LEW/N hypothalami to these neurotransmitters.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗

PubMed1992

Cholecystokinin-octapeptide stimulates hypothalamic-pituitary-adrenal function in rats: role of corticotropin-releasing hormone.

Peripherally-administered cholecystokinin (CCK) is a profound suppressor of food intake, can promote anxiety, and causes the acute release of ACTH into plasma. Centrally administered corticotropin-releasing hormone (CRH), on the other hand, not only represents the principal stimulus to the pituitary corticotroph cell, but also has been shown to suppress appetite and to be profoundly anxiogenic. Because of the overlap in the effects of peripherally administered CCK and of centrally administered CRH, we report here a study to determine whether sulphated CCK octapeptide (CCK-8) could induce the release of CRH within the central nervous system. To accomplish this task, we first assessed the dose-related effects of CCK-8 on ACTH release. Graded doses of CCK-8 (0.1-10 micrograms/kg BW) given in an i.v. bolus to freely moving male rats, resulted in a dose-dependent increase of plasma immunoreactive (IR)-ACTH (ED50: 1-10 micrograms/kg BW). The lowest maximal stimulatory dose of CCK-8 (5 micrograms/kg BW) was used in all subsequent experiments. To evaluate whether CCK-induced ACTH secretion was mediated by a peripheral CCK receptor, an i.v. bolus injection of vehicle or L-364,718 (1 mg/kg BW), a specific, highly potent peripheral CCK receptor antagonist, was given before the i.v. administration of CCK-8 or vehicle. Plasma IR-ACTH response to CCK-8 was significantly attenuated by L-364,718. A role for the vagal afferents that contain CCK receptors in peripherally administered CCK-mediated hypothalamic-pituitary-adrenal (HPA) axis activation was examined in animals that had been pretreated with capsaicin, a potent neurotoxin that destroys vagal afferents. Plasma IR-ACTH and IR-corticosterone responses in capsaicin-treated animals were significantly lower than those in vehicle treated rats. In subsequent in vivo experiments, pituitary stalk-transected and sham-operated animals were used to evaluate whether CCK-8 stimulates the HPA axis via a centrally mediated mechanism. IR-ACTH and IR-corticosterone responses to i.v. CCK-8 were significantly reduced in the pituitary stalk-transected compared to sham-operated animals. In further effort to determine whether the central nervous system was involved in the plasma IR-ACTH response to the peripheral administration of i.v. CCK-8, we compared the effects of the i.v. administration of CRH antisera vs. normal rabbit serum on this parameter. IR-ACTH and IR-corticosterone responses to i.v. CCK-8 were significantly reduced in the context of pretreatment with CRH antisera compared to the administration of normal rabbit serum.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenocorticotropic Hormone↗

PubMed1992

Central hypothyroidism is associated with advanced age in male Fischer 344/N rats: in vivo and in vitro studies.

We investigated age-related alterations in hypothalamic-pituitary-thyroid function in a series of in vivo and in vitro studies in 2-, 8-, 18-, and 24-month-old male Fischer 344/N (F344/N) rats. Thyroid histology showed progressive follicular loss with advancing age; this was associated with significant and progressive decrements in plasma levels of free T4 and free T3, but not immunoreactive TSH, which remained unchanged with age. This was accompanied by a progressive age-dependent loss in in vivo responsivity of the thyrotroph to synthetic TRH and a paradoxically augmented response of GH to this peptide in the oldest rats. Steady state levels of prepro-TRH mRNA in the hypothalamic paraventricular nucleus were decreased with age, whereas TRH content in and in vitro secretion by whole hypothalami remained unchanged. Both anterior pituitary steady state TSH beta-subunit mRNA levels and TSH content were decreased with age. Taken together, these data suggest that aging in male F344/N rats is associated with a progressive, centrally mediated decrease in thyroid function. The relative contributions to this phenomenon of age-related alterations in supra-hypothalamic and/or hypothalamic vs. pituitary thyrotropic function remain to be determined, as do the relationships between changes in hypothalamic-pituitary-thyroid function and those in aging per se.

Aging↗

PubMed1991

Hypothalamic and suprahypothalamic effects of prolonged treatment with dexamethasone in the rat.

Corticosteroid type I and II receptors mediate the negative feedback effects of these hormones at various central nervous system sites involved in the regulation of the hypothalamic-pituitary-adrenal (HPA) axis. To examine the effects of chronic treatment with dexamethasone (DEX), a type 2 receptor agonist, on the regulation of this axis, male Sprague-Dawley rats weighing 200-250 g were given daily injections of DEX for 1,2,3, and 4 weeks or were treated with a subcutaneously implanted DEX-releasing minipump for one week. At the end of treatment, the animals were weighed and brains and truncal blood were collected. Daily intermittent DEX treatment reduced the body weight of the rats in a time-dependent fashion, but had little or no effect on their wet brain weight. Plasma ACTH and corticosterone, measured by RIA, were fully suppressed after one week of intermittent treatment and did not show any further reduction in rats treated for longer periods. In these animals, the content of immunoreactive corticotropin-releasing hormone (iCRH), arginine vasopressin (AVP), ACTH and beta-endorphin (beta-EP) in the hypothalamus, hippocampus, cerebral cortex and cerebellum and pituitary ACTH content did not show any difference compared to vehicle-treated rats. In contrast, continuous DEX treatment increased iCRH content in the cortex, reduced AVP content in the cerebellum, increased ACTH content in the hippocampus, decreased ACTH and beta-EP content in the hypothalamus, and reduced pituitary ACTH content. Hypothalami explanted from rats treated with DEX for one week released lower basal amounts of iCRH in vitro and did not respond to a maximally stimulatory concentration of serotonin (5-HT), a known CRH secretagogue. Continuous DEX administration suppressed also potassium chloride-induced iCRH release. Interestingly, hypothalami explanted from rats receiving daily injection of vehicle, but not from unhandled, untreated controls, did not respond to 5-HT with an increase of iCRH release in vitro. In conclusion, prolonged and continuous, but not intermittent, administration of DEX had a strong effect on brain neuropeptide content. Both regimens of DEX reduced the hypothalamic iCRH responsiveness to stimuli in vitro. Chronic handling also decreased the responsiveness of the hypothalamus to a stimulatory neurotransmitter and may confound the interpretation of data pertinent to inhibitory mechanisms.

Adrenocorticotropic Hormone↗

PubMed1991

Role of peripherally infused angiotensin II on the human hypothalamic-pituitary-adrenal axis.

Although angiotensin II (AII), a potent vasoconstrictor agent, has been reported to stimulate the hypothalamic-pituitary-adrenal (HPA) axis of laboratory animals, its role in the regulation of this axis in humans appears to be controversial. To examine this question, AII (Val5-AII amide) was infused intravenously into 19 male normal volunteers at the doses of 0, 1, 3.3 and 10 ng/kg/min for 30 min. AII had no effect on plasma ACTH, cortisol, corticotrophin-releasing hormone, arginine vasopressin, and atrial natriuretic factor concentrations, nor did it increase systolic or diastolic arterial blood pressure. On the other hand, AII caused a dose-dependent increase of plasma aldosterone concentrations, suggesting that the doses and the mode of AII infusion were effective. Thus, our data show that peripherally infused AII has no detectable effect on the HPA axis function in humans, at doses capable of stimulating plasma aldosterone secretion, its specific target hormone.

Adrenocorticotropic Hormone↗

PubMed1991

Circadian patterns of plasma immunoreactive corticotropin, beta-endorphin, corticosterone and prolactin after immunoneutralization of corticotropin-releasing hormone.

To study the role of corticotropin-releasing hormone (CRH) in the circadian rhythm of circulating corticotropin (ACTH), beta-endorphin (beta-END), corticosterone, and prolactin (PRL), we measured the effects of CRH immunoneutralization over a 24-hour period in chronically cannulated, conscious, freely moving, male Sprague-Dawley rats, maintained at a constant light-dark cycle. Blood samples were collected in the morning (08.00 h), at noon (12.00 h), and in the evening (18.00 h) on the day of treatment, and in the morning (08.00 h) of the next day. Hyperimmune rabbit serum raised against rat CRH (1.0 ml/rat, i.v.) or normal rabbit serum (NRS, 1.0 ml/rat, i.v.) was administered at 08.00 h, immediately after the first blood sample had been collected. CRH immunoneutralization caused no significant decreases in circulating immunoreactive ACTH, beta-END and corticosterone plasma levels at noon, but abolished the evening rises of these hormones. PRL levels were not significantly different between the groups at any time point measured. To compare the effects of CRH immunoneutralization to those of glucocorticoid negative feedback, we measured the effects of dexamethasone (0.5 mg/kg, i.v. at 08.00 h) on the above parameters. ACTH and beta-END concentrations were significantly decreased, and corticosterone and PRL levels were markedly suppressed after glucocorticoid administration both at 12.00 and 18.00 h. However, 24 h after the administration of dexamethasone, PRL concentrations were elevated despite persistently low corticosterone levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗

PubMed1991

Prolactin stimulates rat hypothalamic corticotropin-releasing hormone and pituitary adrenocorticotropin secretion in vitro.

In rats hyperprolactinemia increases corticotropin-releasing hormone (CRH) concentration and secretion in hypophysial portal blood and the serum concentration of adrenocorticotropic hormone (ACTH). To determine whether the stimulatory effect of prolactin (PRL) on CRH and ACTH in vivo is exerted directly on the hypothalamus, hypothalamic explants and primary anterior pituitary cell cultures from adult male and female rats were used. Hypothalami explanted from male and female rats were preincubated during 90 min and treated for 30 min with rat PRL (rPRL) at concentrations of 10(-8), 10(-7), and 10(-6) M (about 200, 2,000, and 20,000 ng/ml, respectively), corticosterone at concentrations of 10(-7), 10(-6), and 10(-5) M (about 35,350 and 3,500 ng/ml, respectively), ACTH at concentrations ranging from 10(-10) to 10(-7) M (0.46, 4.6, 46, and 460 ng/ml, respectively), and graded concentrations of testosterone or estradiol. Concentrations of immunoreactive CRH (iCRH) were measured by radioimmunoassay. rPRL at 10(-6) M stimulated iCRH secretion by 360 and 400% of the basal iCRH output (about 14 pg/hypothalamus), respectively, from hypothalami explanted from male and female rats. ACTH and corticosterone did not suppress rPRL (10(-6) M) induced iCRH secretion. Corticosterone at the concentration of 10(-6) M potentiated rPRL (10(-6) M) induced iCRH secretion in hypothalami explanted from male, but not female rats. Gonadal steroids had no effect either on the basal or rPRL (10(-6) M) stimulated iCRH secretion, with the exception of estradiol which augmented the response to 10(-6) M rPRL by about fivefold, but only at the concentration of 10(-8) M (about 2.7 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗

PubMed1991

Effects of short and long duration hypothyroidism and hyperthyroidism on the plasma adrenocorticotropin and corticosterone responses to ovine corticotropin-releasing hormone in rats.

We report here a study of the plasma ACTH and corticosterone responses to synthetic ovine CRH (oCRH) in hypothyroid and hyperthyroid rats studied 7, 15, and 60 days after either thyroidectomy or the administration of pharmacological doses of T4. The purpose of this study was to further clarify the time-dependent effects of alterations in thyroid status on the functional integrity of the hypothalamic-pituitary-adrenal axis and to aid in the interpretation of the oCRH stimulation test in hypo- and hyperthyroid states. Our data demonstrate that hypothyroid rats have a significant reduction in the cerebrospinal fluid (CSF) levels of corticosterone and a significant decrease in adrenal weight in association with significant increases in the plasma ACTH response to oCRH. On the other hand, the corticosterone response to the ACTH released during the oCRH stimulation test was significantly reduced in hypothyroidism. With increasing duration of thyroidectomy-induced hypothyroidism, there was a progressive fall in CSF corticosterone levels, a progressive increase in the plasma ACTH response to oCRH, and a gradual normalization of the corticosterone responses to the ACTH released during oCRH stimulation. Our findings in hyperthyroid rats were generally the converse of those seen in hypothyroidism. Hence, there was a significant increase in the CSF levels of corticosterone and a significant increase in adrenal weight in association with an initial slight decrease in the ACTH response to oCRH. On the other hand, the corticosterone response to the ACTH released during oCRH stimulation was significantly increased. There was a gradual increase in the magnitude of the rise in CSF corticosterone levels with time, as well as a gradual normalization of adrenocortical responses during oCRH stimulation. The ACTH plasma clearance rates were similar in hypo-, hyper-, and euthyroid rats. Our data do not permit definitive identification of the precise locus in the hypothalamic-pituitary-adrenal axis that is principally affected by experimentally induced alterations in thyroid status. However, these data are most compatible with a subtle hypothyroid-induced centrally mediated adrenal insufficiency and a subtle hyperthyroid-induced centrally mediated hypercortisolism. These data also suggest that alterations in hypothalamic-pituitary-adrenal function in states of disturbed thyroid function become somewhat more pronounced as the duration of thyroid dysfunction increases. The fact that pituitary-adrenal responses to oCRH are consistently altered in states of thyroid dysfunction may be relevant to the clinical interpretation of oCRH stimulation tests.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenocorticotropic Hormone↗

PubMed1990

Beta-endorphin responses to different serotonin agonists: involvement of corticotropin-releasing hormone, vasopressin and direct pituitary action.

Activation of serotonergic neurotransmission has been shown to increase plasma beta-endorphin-like immunoreactivity (beta-End-LI). To study the mechanism(s) of this action, we measured the effects of 3 potent serotonin (5-HT) agonists with different structures and 5-HT receptor binding profiles in conscious unrestrained Sprague-Dawley rats in vivo and in dispersed anterior pituicytes in vitro. The 5-HT1A agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), the 5-HT1C agonist, m-chlorophenylpiperazine (m-CPP), and the 5-HT2 agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), all markedly increased beta-End-LI in plasma in vivo. All 3 responses were blocked by dexamethasone pretreatment. Pituitary stalk transection (PST), as well as pretreatment with rabbit serum hyperimmune against rat corticotropin-releasing hormone (CRH, TS-6) completely abolished beta-End-LI response to 8-OH-DPAT and attenuated the responses by about 60% to DOI. Responses to m-CPP were markedly attenuated in PST rats, but pretreatment with TS-6 had no significant effect. To examine whether vasopressin (AVP) might be involved in the CRH neutralizing antibody-resistant beta-End-LI responses after m-CPP and DOI, we measured AVP concentrations after each agonist, m-CPP, but not DOI or 8-OH-DPAT, significantly elevated circulating AVP levels. As a proof of direct pituitary effect, DOI markedly stimulated beta-End-LI release from the anterior pituitary cell culture preparation in vitro. It was approximately as potent as CRH in the picomolar range, m-CPP was much less effective than DOI, while 8-OH-DPAT did not stimulate beta-End-LI release in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Hydroxy-2-(di-n-propylamino)tetralin↗