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S Karanth

Publications and source records attributed to S Karanth.

At least 37 records · Page 2Linked to original sources
PubMed1999

Estrogen and leptin have differential effects on FSH and LH release in female rats.

Prior experiments have shown that the adipocyte hormone leptin can advance puberty in mice. We hypothesized that it would also stimulate gonadotrophin secretion in adults. Since the secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) is drastically affected by estrogen, we hypothesized that leptin might have different actions dependent on the dose of estrogen. Consequently in these experiments, we tested the effect of injection of leptin into the third cerebral ventricle of ovariectomized animals injected with either the oil diluent, 10 microg or 50 microg of estradiol benzoate 72 hr prior to the experiment. The animals were ovariectomized 3-4 weeks prior to implantation of a cannula into the third ventricle 1 week before the experiments. The day after implantation of an external jugular catheter, blood samples (0. 3 ml) were collected just before and every 10 min for 2 hr after 3V injection of 5 microl of diluent or 10 microg of leptin. Both doses of estradiol benzoate equally decreased plasma LH concentrations and pulse amplitude, but there was a graded decrease in pulse frequency. In contrast, only the 50-microg dose of estradiol benzoate significantly decreased mean plasma FSH concentrations without significantly changing other parameters of FSH release. The number of LH pulses alone and pulses of both hormones together decreased as the dose of estrogen was increased, whereas the number of pulses of FSH alone significantly increased with the higher dose of estradiol benzoate, demonstrating differential control of LH and FSH secretion by estrogen, consistent with alterations in release of luteinizing hormone releasing hormone (LHRH) and the putative FSH-releasing factor (FSHRF), respectively. The effects of intraventricularly injected leptin were drastically altered by increasing doses of estradiol benzoate. There was no significant effect of intraventricular injection of leptin (10 microg) on the various parameters of either FSH or LH secretion in ovariectomized, oil-injected rats, whereas in those injected with 10 microg of estradiol benzoate there was an increase in the first hr in mean plasma concentration, area under the curve, pulse amplitude, and maximum increase of LH above the starting value (Deltamax) on comparison with the results in the diluent-injected animals in which there was no alteration of these parameters during the 2 hr following injection. The pattern of FSH release was opposite to that of LH and had a different time-course. In the diluent-injected animals, probably because of the stress of injection and frequent blood sampling, there was an initial significant decline in plasma FSH at 20 min after injection, followed by a progressive increase with a significant elevation above the control values at 110 and 120 min. In the leptin-injected animals, mean plasma FSH was nearly constant during the entire experiment, coupled with a significant decrease below values in diluent-injected rats, beginning at 30 min after injection and progressing to a maximal difference at 120 min. Area under the curve, pulse amplitude, and Deltamax of FSH was also decreased in the second hour compared to values in diluent-injected rats. In contrast to the stimulatory effects of intraventricular injection of leptin on pulsatile LH release manifest during the first hour after injection, there was a diametrically opposite, delayed significant decrease in pulsatile FSH release. This differential effect of leptin on FSH and LH release was consistent with differential effects of leptin on LHRH and FSHRF release. Finally, the higher dose of E2 (50 microg) suppressed release of both FSH and LH, but there was little effect of leptin under these conditions, the only effect being a slight (P < 0.04) increase in pulse amplitude of LH in this group of rats. The results indicate that the central effects of leptin on gonadotropin release are strongly dependent on plasma estradiol levels. These effects are consistent w

Activity Cycles↗
PubMed1999

The role of nitric oxide in reproduction.

Nitric oxide (NO) plays a crucial role in reproduction at every level in the organism. In the brain, it activates the release of luteinizing hormone-releasing hormone (LHRH). The axons of the LHRH neurons project to the mating centers in the brain stem and by afferent pathways evoke the lordosis reflex in female rats. In males, there is activation of NOergic terminals that release NO in the corpora cavernosa penis to induce erection by generation of cyclic guanosine monophosphate (cGMP). NO also activates the release of LHRH which reaches the pituitary and activates the release of gonadotropins by activating neural NO synthase (nNOS) in the pituitary gland. In the gonad, NO plays an important role in inducing ovulation and in causing luteolysis, whereas in the reproductive tract, it relaxes uterine muscle via cGMP and constricts it via prostaglandins (PG).

Animals↗
PubMed1998

Reduced activity of hypothalamic corticotropin-releasing hormone neurons in transgenic mice with impaired glucocorticoid receptor function.

Loss of central glucocorticoid receptor (GR) function is thought to be involved in the development of neuroendocrine and psychiatric disorders associated with corticotropin-releasing hormone (CRH) hyperactivity. The possible causal relationship between defective GR function and altered activity of CRH neurons was studied in transgenic mice (TG) expressing antisense RNA against GR. Immunocytochemical studies showed significant reductions in CRH immunoreactive neurons in the paraventricular nucleus (PVN) and in CRH and vasopressin (AVP) stores in the external zone of the median eminence. Concomitantly, stimulus-evoked CRH secretion from mediobasal hypothalami of TG mice in vitro was reduced significantly. However, CRH mRNA levels in the PVN of TG mice were marginally lower than those in wild-type (WT) mice. 125I-CRH binding autoradiography revealed no differences between WT and TG animals in any of the brain regions that were studied. Basal plasma corticosterone (cort) levels and 125I-CRH binding, CRH-R1 mRNA, POMC mRNA, and POMC hnRNA levels in the anterior pituitary gland were similar in WT and TG mice. Intraperitoneal injection of interleukin-1beta (IL-1beta) increased plasma cort levels, CRH mRNA in the PVN, and anterior pituitary POMC hnRNA similarly in WT and TG mice. The injection of saline significantly reduced anterior pituitary CRH-R1 mRNA levels in WT mice, but not in TG mice, whereas IL-1beta produced a decrease in these mRNA levels in both strains. The data show that long-term GR dysfunction can be associated with reduced activity of CRH neurons in the PVN and decreased sensitivity of pituitary CRH-R1 mRNA to stimulus-induced downregulation. Moreover, the hypothalamic changes observed in this model suggest that impaired GR function, at least if present since early embryonic life, does not necessarily result in CRH hyperexpression characteristics of disorders such as major depression.

Animals↗
PubMed1998

Role of nitric oxide in the neuroendocrine responses to cytokines.

During infection, bacterial and viral products, such as bacterial lipopolysaccharide (LPS), cause the release of cytokines from immune cells. These cytokines can reach the brain by several routes. Furthermore, cytokines, such as interleukin-1 (IL-1), are induced in neurons within the brain by systemic injection of LPS. These cytokines determine the pattern of hypothalamic-pituitary secretion which characterizes infection. IL-2, by stimulation of cholinergic neurons, activates neural nitric oxide synthase (nNOS). The nitric oxide (NO) released diffuses into corticotropin-releasing hormone (CRH)-secreting neurons and releases CRH. IL-2 also acts in the pituitary to stimulate adrenocorticotropic hormone (ACTH) secretion. On the other hand, IL-1 alpha blocks the NO-induced release of luteinizing hormone-releasing hormone (LHRH) from LHRH neurons, thereby blocking pulsatile LH but not follicle-stimulating hormone (FSH) release and also inhibiting sex behavior that is induced by LHRH. IL-1 alpha and granulocyte macrophage colony-stimulating factor (GMCSF) block the response of the LHRH terminals to NO. The mechanism of action of GMCSF to inhibit LHRH release is as follows. It acts on its receptors on gamma-aminobutyric acid (GABA)ergic neurons to stimulate GABA release. GABA acts on GABAa receptors on the LHRH neuronal terminal to block NOergic stimulation of LHRH release. This concept is supported by blockade of GMCSF-induced suppression of LHRH release from medial basal hypothalamic explants by the GABAa receptor blocker, bicuculline. IL-1 alpha inhibits growth hormone (GH) release by inhibiting GH-releasing hormone (GHRH) release, which is mediated by NO, and stimulating somatostatin release, also mediated by NO. IL-1 alpha-induced stimulation of prolactin release is also mediated by intrahypothalamic action of NO, which inhibits release of the prolactin-inhibiting hormone dopamine. The actions of NO are brought about by its combined activation of guanylate cyclase-liberating cyclic guanosine monophosphate (cGMP) and activation of cyclooxygenase and lipoxygenase with liberation of prostaglandin E2 and leukotrienes, respectively. Thus, NO plays a key role in inducing the changes in release of hypothalamic peptides induced in infection by cytokines. Cytokines, such as IL-1 beta, also act in the anterior pituitary gland, at least in part via induction of inducible NOS. The NO produced inhibits release of anterior pituitary hormones.

Animals↗
PubMed1998

Hypothalamic control of gonadotropin secretion by LHRH, FSHRF, NO, cytokines, and leptin.

Gonadotropin secretion by the pituitary gland is under the control of luteinizing hormone-releasing hormone (LHRH) and the putative follicle stimulating hormone-releasing factor (FSHRF). Lamprey III LHRH is a potent FSHRF in the rat and seems to be resident in the FSH controlling area of the rat hypothalamus. It is an analog of mammalian LHRH and may be the long sought FSHRF. Gonadal steroids feedback at hypothalamic and pituitary levels to either inhibit or stimulate the release of LH and FSH, which is also affected by inhibin and activin secreted by the gonads. Important control is exercised by acetylcholine, norepinephrine (NE), dopamine, serotonin, melatonin, and glutamic acid (GA). Furthermore, LH and FSH also act at the hypothalamic level to alter secretion of gonadotropins. More recently, growth factors have been shown to have an important role. Many peptides act to inhibit or increase release of LH and the sign of their action is often reversed by estrogen. A number of cytokines act at the hypothalamic level to suppress acutely the release of LH but not FSH. NE, GA, and oxytocin stimulate LHRH release by activation of neural nitric oxide synthase (nNOS). The pathway is as follows: oxytocin and/or GA activate NE neurons in the medial basal hypothalamus (MBH) that activate NOergic neurons by alpha, (alpha 1) receptors. The NO released diffuses into LHRH terminals and induces LHRH release by activation of guanylate cyclase (GC) and cyclooxygenase. NO not only controls release of LHRH bound for the pituitary, but also that which induces mating by actions in the brain stem. An exciting recent development has been the discovery of the adipocyte hormone, leptin, a cytokine related to tumor necrosis factor (TNF) alpha. In the male rat, leptin exhibits a high potency to stimulate FSH and LH release from hemipituitaries incubated in vitro, and increases the release of LHRH from MBH explants. LHRH and leptin release LH by activation of NOS in the gonadotropes. The NO released activates GC that releases cyclic GMP, which induces LH release. Leptin induces LH release in conscious, ovariectomized estrogen-primed female rats, presumably by stimulating LHRH release. At the effective dose of estrogen to activate LH release, FSH release is inhibited. Leptin may play an important role in induction of puberty and control of LHRH release in the adult as well.

Animals↗
PubMed1997

A hypothalamic follicle-stimulating hormone-releasing decapeptide in the rat.

Previous studies indicated that there is a separate hypothalamic control of follicle-stimulating hormone (FSH) release distinct from that of luteinizing hormone (LH). An FSH-releasing factor (FSHRF) was purified from rat and sheep hypothalami, but has not been isolated. We hypothesized that FSHRF might be an analogue of mammalian luteinizing hormone-releasing hormone (m-LHRH) and evaluated the activity of many analogues of m-LHRH and of the known LHRHs found in lower forms. Here we demonstrate that lamprey (l) LHRH-III has a potent, dose-related FSH- but not LH-releasing action on incubated hemipituitaries of male rats. l-LHRH-I on the other hand, had little activity to release either FSH or LH. m-LHRH was equipotent to l-LHRH-III to release FSH, but also had a high potency to release LH in contrast to l-LHRH-III that selectively released FSH. Chicken LHRH-II had considerable potency to release both LH and FSH, but no selectivity in its action. Salmon LHRH had much less potency than the others tested, except for l-LHRH-I, and no selectivity in its action. Because ovariectomized, estrogen, progesterone-treated rats are a sensitive in vivo assay for FSH- and LH-releasing activity, we evaluated l-LHRH-III in this assay and found that it had a completely selective stimulatory effect on FSH release at the two doses tested (10 and 100 pmols). Therefore, l-LHRH-III is a highly potent and specific FSH-releasing peptide that may enhance fertility in animals and humans. It may be the long sought after m-FSHRF.

Animals↗
PubMed1997

Role of leptin in hypothalamic-pituitary function.

A defect in the structure of the obese gene is responsible for development of obesity in the ob/ob mouse. The product of expression of the gene is the protein hormone leptin. Leptin causes weight loss in ob/ob and normal mice, it is secreted by adipocytes, and it is an important controller of the size of fat stores by inhibiting appetite. The ob/ob mouse is infertile and has a pattern of gonadotropin secretion similar to that of prepubertal animals. Consequently, we hypothesized that leptin might play a role in the control of gonadotropin secretion and initiated studies on its possible acute effects on hypothalamic-pituitary function. After a preincubation period, hemi-anterior pituitaries of adult male rats were incubated with leptin for 3 hr. Leptin produced a dose-related increase in follicle-stimulating hormone (FSH) and luteinizing hormone (LH) release, which reached peaks with 10(-9) and 10(-11) M leptin, respectively. Gonadotropin release decreased at higher concentrations of leptin to values indistinguishable from that of control pituitaries. On the other hand, prolactin secretion was greatly increased in a dose-related manner but only with leptin concentrations (10(-7)-10(-5) M). Incubation with leptin of median eminence-arcuate nuclear explants from the same animals produced significant increases in LH-releasing hormone (LHRH) release only at the lowest concentrations tested (10(-12)-10(-10) M). As the leptin concentration was increased, LHRH release decreased and was significantly less than control release at the highest concentration tested (10(-6) M). To determine if leptin can also release gonadotropins in vivo, ovariectomized females bearing implanted third ventricle cannulae were injected with 10 microg of estradiol benzoate s.c., followed 72 hr later by microinjection into the third ventricle of leptin (0.6 nmol in 5 microl) or an equal volume of diluent. There was a highly significant increase in plasma LH, which peaked 10-50 min after injection of leptin. Leptin had no effect on plasma FSH concentrations, and the diluent had no effect on either plasma FSH or LH. Thus, leptin at very low concentrations stimulated LHRH release from hypothalamic explants and FSH and LH release from anterior pituitaries of adult male rats in vitro and released LH, but not FSH, in vivo. The results indicate that leptin plays an important role in controlling gonadotropin secretion by stimulatory hypothalamic and pituitary actions.

Animals↗
PubMed1997

Nitric oxide mediates leptin-induced luteinizing hormone-releasing hormone (LHRH) and LHRH and leptin-induced LH release from the pituitary gland.

Previous experiments have demonstrated that leptin releases luteinizing hormone-releasing hormone (LHRH) from median eminence (ME)-arcuate explants from male rats and also stimulates the release of follicle-stimulating hormone (FSH) and LH from anterior pituitaries with a potency not significantly different from that of LHRH itself. To determine the mechanism by which leptin acts at both the hypothalamic and pituitary level, we evaluated the effect of a competitive inhibitor of nitric oxide synthase (NOS), NG-monomethyl-L-arginine (NMMA) on the response to leptin. To evaluate the role of NO in the action of leptin to release LHRH, ME-arc explants were incubated with leptin (10[-11] M), a concentration shown earlier to give the most effective stimulation of LHRH release. NMMA (3 x 10[-4] M) completely inhibited the LHRH release induced by leptin. In other experiments, hemi-anterior pituitaries were incubated with NMMA with and without leptin at various concentrations (10[-9] - 10[-6] M). As in the case of hypothalamic explants, NMMA had no effect on basal release of LH; however, it completely blocked the stimulation of LH release induced by leptin. Interestingly, the release of LH induced by LHRH (4 x 10[-9] M) was also completely blocked by the inhibitor of NOS. The results provide evidence that leptin acts both at hypothalamic and pituitary level to stimulate NO release, presumably by acting on its receptors at both sites which then induces the release of either LHRH or LH, respectively. Furthermore, LH release induced by LHRH is also mediated by NO.

Animals↗
PubMed1997

Hypothalamic-pituitary-adrenocortical axis changes in a transgenic mouse with impaired glucocorticoid receptor function.

Recently, a transgenic mouse with impaired glucocorticoid receptor (GR) function was created to serve as an animal model for the study of neuroendocrine changes occurring in stress-related disorders, such as major depression. Here, we investigated the hypothalamic-pituitary-adrenocortical (HPA) axis changes in these transgenic mice. There were no significant differences between basal early morning plasma ACTH and corticosterone levels in normal and transgenic mice. When animals were exposed to a mild stressor, an enhanced response in plasma ACTH was observed in the transgenic mice, whereas plasma corticosterone responses were not different. In view of these differences in plasma ACTH and corticosterone responses, we directed our studies toward the regulation of ACTH secretion on the hypothalamic-hypophyseal level in vitro. Therefore, an in vitro model, the pituitary-hypothalamic complex (PHc) was developed and its ACTH release profile was compared with that of the pituitary (PI) alone. The basal ACTH release by PHc and PI from normal and transgenic mice was similar. Regardless of the strain under study, the basal ACTH release by PI was significantly lower than the release by PHc. Stimulation of tissues with either high K+ (56 mM) or CRH (10 or 20 nM) produced an enhanced ACTH release from both PHc and PI, whereas the response in PI was larger than that in PHC. Moreover, the responses to these stimuli were markedly enhanced in tissues from transgenic mice. In tissues of normal mice, corticosterone inhibited both basal and CRH-stimulated ACTH release more potently in PHc than in PI. Furthermore, the feedback capacity of corticosterone to restrain both basal and CRH-stimulated ACTH release was highly impaired in tissues of transgenic mice, whereas the feedback in PHc appeared to be more affected than that in the PI of these animals. In conclusion, the in vitro data on PHc and PI revealed intrahypothalamic mechanisms operating 1) to fine-tune stimulus-evoked ACTH responses; and 2) to facilitate the negative feedback action of glucocorticoids. Moreover, in the transgenic tissues, the impaired GR function was found to cause augmented stimulus-evoked ACTH responses and an impaired glucocorticoid feedback efficacy which appeared to be mainly defective at the hypothalamic level. Thus, in the transgenic mice with life-long central GR dysfunction we found impaired negative feedback combined with "normal" (i.e. noncompensated) in vivo plasma corticosterone responses. This is a condition with potentially grave pathophysiological consequences and, therefore, this transgenic animal may be regarded as a valuable model for the study of functional glucocorticoid insufficiency at the central nervous system level.

Adrenocorticotropic Hormone↗
PubMed1996

Neurotoxicity and pattern of acetylcholinesterase inhibition in the brain regions of rat by bromophos and ethylbromophos.

Bromophos (Bp) and ethylbromophos (EBp) are two structurally homologous organophosphorus (OP) insecticides which show wide differences in their toxicity as well as neurotoxic symptoms in the laboratory rat. EBp is 24-fold more toxic (LD50 = 91 +/- 14 mg/kg body wt) than Bp (LD50 = 2218 +/- 195 mg/kg body wt) and only EBp produced characteristic tremors and lacrimation. In vivo cholinesterase inhibition was in the order plasma > erythrocytes > brain. Experiments with equitoxic and equimolar doses showed that EBp is a more potent anticholinesterase compound than Bp. Since IC50 values for the brain AChE were similar for both OPs, the target enzyme sensitivity was not a major factor in their differential toxicity. In vitro reactivation of serum ChE was significantly higher in the case of EBp than that of Bp. AChE in the brain regions showed differential inhibition in vivo. The brain stem AChE inhibition was least by Bp, whereas it was highest in the case of EBp. Both the OPs produced high AChE inhibition in the hippocampus. Differential inhibition of AChE in the brain regions and its consequent effects may be important factors in the differential neurotoxicity of OPs.

Animals↗
PubMed1996

The role of nitric oxide (NO) in control of hypothalamic-pituitary function.

Neurons containing neural nitric oxide synthase (nNOS) are found in various locations in the hypothalamus and, in particular, in the paraventricular and supraoptic nuclei with axons which project to the median eminence and extend into the neural lobe where the highest concentrations of NOS are found in the rat. Furthermore, nNOS is also located in folliculostellate cells and LH gonadotropes in the anterior pituitary gland. To define the role of NO in the release of hypothalamic peptides and pituitary hormones, we injected an inhibitor of NOS, Ng-monomethyl-L-arginine (NMMA) or a releasor of NO, nitroprusside (NP) into the third ventricle (3V) of conscious castrate rats and determined the effect on the release of various pituitary hormones. In vitro, we incubated medial basal hypothalamic (MBH) fragments and studied inhibitors of NO synthase and also releasors of NO. The results indicate that NOergic neurons play an important role in stimulating the release of corticotrophin-releasing hormone (CRH), luteinizing hormone releasing-hormone (LHRH), prolactin-RH's, particularly oxytocin, growth hormone-RH (GHRH) and somatostatin, but not FSH-releasing factor from the hypothalamus. NO stimulates the release of LHRH, which induces sexual behavior, and causes release of LH from the pituitary gland. The intrahypothalamic pathway by which NO controls LHRH release is as follows: glutamergic neurons synapse with noradrenergic terminals in the MBH which release nonepinephrine (NE) that acts on alpha 1 receptors on the NOergic neuron to increase intracellular free Ca++ which combines with calmodulin to activate NOS. The NOS diffuses to the LHRH terminal and activates guanylate cyclase (GC), cyclooxygenase and lipoxygenase causing release of LHRH via release of cyclic GMP, PGE2 and leukotrienes, respectively. Alcohol and cytokines can block LHRH release by blocking the activation of cyclooxygenase and lipoxygenase without interfering with the activation of GC. GABA also blocks the response of the LHRH neurons to NO and recent experiments indicate that granulocyte macrophage colony-stimulating factor (GMCSF) blocks the response of the LHRH neuron to NP by activation of GABA neurons since the blockade can be reversed by the competitive inhibitor of GABAa receptors, bicuculine.

Adrenocorticotropic Hormone↗
PubMed1995

A longitudinal study of granulocyte colony-stimulating factor levels and neutrophil counts in newborn infants.

PURPOSE: The goal of this study was to longitudinally measure endogenous granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) levels in newborn infants and to attempt to correlate these levels with neutrophil counts. PATIENTS AND METHODS: Samples for complete blood count, G-CSF, and GM-CSF were obtained from groups of healthy full-term infants at 0 (cord blood or nursery admission), 12, 24, 48, and 72 h. Samples were also obtained from premature infants at the above times and at 1 week. G-CSF and GM-CSF levels were measured using bioassays. RESULTS: Levels of G-CSF ranged from < 5 to 53,800 pg/ml. Levels were significantly higher (p < 0.001) in premature infants and decreased over time in all infants. White blood cell counts also decreased over the first week of life. All GM-CSF levels were below the detectable range. CONCLUSIONS: Levels of G-CSF at birth are higher than those seen in adults. These increased levels may partially explain the leukocytosis seen in the first week of life. This, as has been shown in preliminary studies, suggests that infants are capable of an increase in neutrophil count after administration of exogenous G-CSF.

Cell Cycle↗
PubMed1995

Changes in level of certain serum constituents following sciatectomy in the common frog, Rana tigrina (Daud).

Effect of unilateral (one leg) and bilateral (two legs) sciatectomy was studied on certain serum constituents in the male frog over a period of 3 weeks. The level of creatine kinase, acid and alkaline phosphatases, urea, glucose and proteins increased initially following sciatectomy and decreased subsequently from day 14 onwards, the per cent change being more pronounced in case of bilaterally sciatectomized frogs. The present results indicate an increase in the rate of deamination of proteins in the liver, an impairment in the transportation processes across the cell membrane and an increase in cellular lysosomal activity on sciatectomy suggesting a change either in the amount or in the rate of various enzyme reactions. It is concluded that sciatectomy induces alterations in general metabolic activities and the functional state of the animal. Altered values of various serum constituents thus permit to speculate analysis of the factor that may be contributing to the atrophic processes and the wasting of the muscle fibres known to set in the denervated muscle.

Animals↗
PubMed1994

Cyclosporin A inhibits interleukin-2-induced release of corticotropin-releasing hormone.

Cyclosporin A (CSA), a potent immunosuppressive drug, has recently been shown to bind with high affinity to the immunophilin, cyclophilin. Calcineurin, the calcium-dependent protein phosphatase, binds the cyclophilin/CSA complex, rendering it inactive and blocking dephosphorylation of phosphoproteins. Very high concentrations of cyclophilin have been reported in the brain with a localization identical to that of calcineurin. We have reported that interleukin-2 (IL-2) releases corticotropin-releasing hormone (CRH) by generation of nitric oxide (NO). Nitric oxide synthase (NOS), the enzyme in nitric oxidergic neurons that converts arginine into citrulline plus NO, is inactive in the phosphorylated state. We hypothesized that cyclosporin might therefore inhibit IL-2-induced acute CRH release by blocking the dephosphorylation of NOS by calcineurin. Consequently, we examined the effect of CSA on the release of CRH from mediobasal hypothalami (MBH) in vitro in 'basal' conditions and in the presence of IL-2, which we had previously shown to stimulate CRH release acutely in this preparation. Incubation of MBH for 30 min with IL-2 (10(-13) M), the concentration that was most effective in previous experiments, evoked a significant release of CRH. CSA at 10(-6) or 10(-8) M did not alter basal release of CRH; however, addition of either concentration completely blocked the IL-2-induced release of CRH. This acute action of CSA within the brain is probably mediated by blockade of the dephosphorylation of NOS by calcineurin.

Animals↗
PubMed1993

Role of nitric oxide in interleukin 2-induced corticotropin-releasing factor release from incubated hypothalami.

Stimulation of corticotropin-releasing factor (CRF) release from the hypothalamus by interleukin 2 (IL-2) was recently demonstrated. Cytokines induce nitric oxide synthase (NOS), an enzyme that converts L-arginine into L-citrulline and nitric oxide (NO). NO is believed to be responsible for the cytotoxic action of these agents. The constitutive form of NOS occurs in neurons in the central nervous system and NO appears to play a neurotransmitter role in cerebellar and hippocampal function. We explored the probability that IL-2 and synaptic transmitters might release CRF via NO. The effects of L-arginine, the substrate for NOS, and NG-monomethyl-L-arginine (NMMA), a competitive inhibitor of NOS, on IL-2-induced CRF release were studied using mediobasal hypothalami (MBHs) incubated in vitro in Krebs-Ringer bicarbonate buffer. L-Arginine did not alter basal and IL-2-induced CRF release after 30 min of incubation but significantly elevated both basal and IL-2-induced CRF release when MBHs were incubated 30 min longer, presumably because the endogenous substrate had been depleted after the initial 30-min incubation period. In 30-min incubations, both carbachol, an acetylcholineomimetic drug, and norepinephrine stimulated CRF release. There was an additive effect of incubation of the MBHs in the presence of carbachol (10(-7) M) and IL-2 (10(-13) M). On the other hand, coincubation of MBHs with norepinephrine (10(-6) M) and IL-2 (10(-13) M) did not produce any additive effect. Addition of NMMA, an inhibitor of NOS, at 1 or 3 x 10(-4) M completely suppressed IL-2-induced release of CRF as well as that caused by IL-2 plus carbachol. In contrast, the release of CRF induced by norepinephrine was not blocked by 3 x 10(-4) M NMMA. The data indicate that IL-2 can activate constitutive NOS leading to increased NO release, which activates CRF release. It appears that NO is also involved in the release of CRF induced by carbachol but not by norepinephrine.

Animals↗