Biomedical subjects

L A Frohman

Publications and source records attributed to L A Frohman.

At least 91 records · Page 5Linked to original sources

PubMed1989

Beta-adrenergic modulation of growth hormone (GH) autofeedback on sleep-associated and pharmacologically induced GH secretion.

To determine whether GH feedback affects both induced and spontaneous GH secretion and to explore its neurotransmitter mediation, we assessed the effects of 6-h GH infusions (0.55-5.5 micrograms/m2/min) on sleep-associated and GH-releasing hormone (GHRH)-, insulin hypoglycemia-, and arginine-stimulated GH secretion and their modulation by beta-adrenergic blockade in normal men. GH infusions initiated 2 h before the expected onset of sleep produced a dose-dependent inhibition of GH secretion. GH infusions (0.55 micrograms/m2/min) initiated 4 h before the stimuli inhibited the GH response to each, but did not alter the TSH response to TRH. Propranolol infusion (80 micrograms/min) started 2 h before the onset of sleep or the stimulus enhanced GH responses to GHRH and insulin alone and in the presence of GH. In contrast, propranolol neither enhanced the GH responses to arginine or sleep nor reversed the inhibitory effects of GH. The negative feedback effect of GH to both physiological and pharmacological stimuli of GH secretion indicates that it is most likely mediated by both stimulation of somatostatin and inhibition of GHRH release. The effects of beta-adrenergic blockade suggest an inhibition of somatostatin release, although the complex interaction of GH and propranolol implies that they act through dissimilar mechanisms.

Adult↗

PubMed1989

Cloning and characterization of mouse growth hormone-releasing hormone (GRH) complementary DNA: increased GRH messenger RNA levels in the growth hormone-deficient lit/lit mouse.

We have isolated and cloned the full length cDNA for mouse GH-releasing hormone (mGRH) from mouse hypothalamus using a recently described strategy involving the polymerase chain reaction technique (PCR). Degenerate oligonucleotide primers were selected based on short (six amino acids) conserved regions in the human and rat GRH peptides that would recognize DNA sequences encoding similar amino acids regardless of codon usage. Primer-extended cDNA was amplified by PCR on cDNA templates prepared by reverse transcribing total mouse hypothalamic RNA. After cloning and sequencing the initial product, the 3' and 5' ends of mGRH were generated using a separate PCR strategy (RACE protocol). The mGRH cDNA encodes a 103-amino acid reading frame, structurally similar to the human and rat GRH genes, containing a signal sequence, a 42-residue GRH peptide, and a 31-residue C-terminal region. Although the structures of mouse and rat GRH are highly conserved in the signal peptide and C-terminal region, there is considerable diversity in the GRH region, which exhibits nearly comparable homology with the rat (68%) and human (62%) structures. Differences between mouse and rat GRH were also found in the amino acid cleavage sites at the 5' and 3' ends of the mature peptide and at the polyadenylation signal.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

The role of hypothalamic hormones in the control of growth hormone secretion and of growth.

GHRH and somatostatin have major integrative roles in the control of GH secretion. Alterations in the secretion of each hypothalamic hormone have profound effects on GH secretion. On the basis of current information, it appears that disturbances in GHRH secretion provide a most convincing argument for the pathophysiological role of this hypothalamic hormone in clinically recognized disorders of GH secretion. Thus, the potential use of GHRH and its agonists and antagonists in the treatment of patients with both deficient and excessive GH secretion is based on a solid framework of physiological and pathophysiological studies.

Animals↗

PubMed1988

Radio-frequency vs. electrolytic VMH lesions: differential effects on plasma hormones.

Electrolytic lesions of the ventromedial hypothalamus (VMH) result in marked hyperphagia and obesity, but several studies have found the excess food intake and weight gain to be greatly reduced when lesions are produced by electrocauterization with radio-frequency current. Unlike electrolytic lesions, radio-frequency lesions leave few or no deposits of metallic ions that can potentially stimulate adjacent tissue. In the present experiment, weight gain and several endocrine responses previously associated with the VMH syndrome were compared in female rats given either electrolytic, radio-frequency, or sham VMH lesions. Both groups with VMH lesions became obese, but rats with radio-frequency lesions displayed only 63.2% of the weight gain of animals with irritative lesions (120.0 vs. 189.8 g in 20 days). Only rats with electrolytic lesions displayed elevated plasma insulin levels during an initial period of food restriction, but both groups with lesions were hyperinsulinemic when allowed to overeat. Plasma growth hormone levels were decreased by electrolytic lesions but unaffected by radio-frequency lesions. Morning corticosterone levels were elevated in both VMH groups, but only the rats with electrolytic lesions were found to have elevations in plasma adrenocorticotropin. It is concluded that some of the endocrine dysfunctions resulting from electrolytic VMH lesions are due to irritative stimulation rather than to tissue ablation.

Animals↗

PubMed1988

Growth hormone enhances hepatic epidermal growth factor receptor concentration in mice.

The effect of growth hormone (GH) on binding of epidermal growth factor (EGF) to liver membrane preparations was investigated in hypophysectomized mice and partially GH-deficient, genetic mutant "little" (lit/lit) mice. The EGF binding of normal male mice and testosterone-treated females was higher than in normal females. Due to diminished receptor concentration, hepatic EGF binding was decreased in male and female lit/lit mice to a level that was unaffected by gender or androgen treatment. GH replacement therapy by intermittent injections and continuous infusion restored the EGF binding of hypophysectomized mice to normal male and female levels, respectively, suggesting a role for the more pulsatile GH secretion in normal males. In lit/lit mice, however, both continuous and intermittent GH resulted in EGF binding levels comparable to those in normal females. In normal males continuous GH suppressed EGF binding. In conclusion, endogenous GH secretion induces EGF receptors in mice and this effect may be modulated by sex differences in GH secretion.

Animals↗

PubMed1988

Inhibitory effect of hypothalamic medial preoptic area somatostatin on growth hormone-releasing factor in the rat.

Possible inhibitory effects of somatostatin (SRIF) on GRF were studied by assessing spontaneous GH secretion and GRF content and release in adult male rats depleted of hypothalamic SRIF by anterolateral hypothalamic deafferentation (AHD) or electrolytic lesions in the medial preoptic area (MPO). Plasma GH levels were measured 7 days postoperatively every 20 min in conscious animals with indwelling iv cannulae. Median eminence SRIF was markedly reduced 8 days postoperatively in both AHD and MPO rats, as determined by immunohistochemistry and RIA (P less than 0.01). Although GRF immunoreactivity in the median eminence of AHD and MPO animals appeared well preserved immunocytochemically, hypothalamic GRF content by RIA was significantly decreased at 8 days (P less than 0.01). Spontaneous GH secretion was pulsatile in sham-operated animals. In contrast, basal GH levels in AHD and MPO animals were markedly elevated (P less than 0.01), and secretory pulses were absent. Intravenous injection of specific anti-GRF serum into MPO animals decreased the elevated plasma GH levels (P less than 0.01), indicating increased hypothalamic GRF secretion. GRF release from hypothalamic median eminence-arcuate nucleus complexes in vitro was significantly greater in AHD and MPO animals than in control animals 4 and 8 days postoperatively in response to 30 mM K+ (P less than 0.01), but not under basal conditions. These results suggest that hypothalamic medial preoptic area somatostatinergic neurons play a tonic inhibitory role in the regulation of GRF release and that GH hypersecretion observed after MPO and AHD is attributable to changes in both SRIF and GRF.

Animals↗

PubMed1988

Growth hormone synthesis and secretion by a somatomammotroph cell line derived from normal adult pituitary of the rat.

A somatomammotroph cell line derived from male rat anterior pituitary (rPCO) has been established without the use of transforming agents and has been maintained in culture for more than 1 yr (45 passages) using Minimum Essential Medium supplemented with 10% horse serum, 5 nM T3, 2 nM corticosterone, and 0.1 nM GH-releasing hormone (GRH). Peroxidase and immunofluorescent staining revealed immunoreactive GH in 99% of rPCO cells and immunoreactive PRL in 72% of cells. Within individual cells, GH and PRL appear to be colocalized. The storage capacity for GH in rPCO cells represented 40% of the daily hormone production. In serum-free medium containing 5 nM cortisol, GH secretion was stimulated 10- and 25-fold by 50 pM and 50 nM T3, respectively. GRH (1 nM) stimulated GH secretion 8-fold in the absence of T3, although no effect was observed in the presence of 50 nM T3. Qualitatively similar changes occurred in GH mRNA responses to T3 and GRH. Other secretory proteins were detected on sodium dodecyl sulfate-polyacrylamide gel electrophoresis of culture medium, several of which were present in concentrations similar to that of GH. Nine separate cell lines were cloned from rPCO cells by limiting dilution, all of which secreted GH and PRL. GH secretion varied 6-fold between clones, and the GH to PRL ratio varied more than 200-fold. These rPC cell lines provide a new model for studying the control of GH and PRL gene expression, including hormone synthesis, processing, and secretion. They may also be useful for identifying other pituitary secretory products and as a source for the production of protein hormones.

Adrenocorticotropic Hormone↗

PubMed1988

Differential effects of somatostatin (SRIH) and a SRIH analog, SMS 201-995, on the secretion of growth hormone and thyroid-stimulating hormone in man.

We compared the ability of SRIH and SRIH analog, SMS 201-995 (SMS), to inhibit stimulated GH and TSH secretion in men who received 120-min iv infusions of saline, SRIH (5, 50, and 500 micrograms/h), and SMS (3, 30, and 300 ng/kg.h) together with a bolus iv injection of GHRH (1 microgram/kg) and TRH (500 micrograms). Integrated GH secretion during the 60 min after GHRH plus TRH injection was decreased compared to that after saline by (mean +/- SE) 32 +/- 14% (P = 0.059), 78 +/- 5% (P less than 0.001), and 88 +/- 3% (P less than 0.001) during the 5, 50, and 500 micrograms/h SRIH infusions, and by 13 +/- 7% (P = NS), 50 +/- 15% (P less than 0.05), and 80 +/- 6% (P less than 0.001) during the 3, 30, and 300 ng/kg.h SMS infusions. In contrast, integrated TSH secretion was unaltered during the 5 micrograms/h SRIH and 3 ng/kg.h SMS infusions; it decreased by only 43 +/- 5% (P less than 0.001) and 66 +/- 4% (P less than 0.001) during the 50 and 500 micrograms/h SRIH infusions and by 33 +/- 8% (P less than 0.05) and 50 +/- 3% (P less than 0.001) during the 30 and 300 ng/kg.h SMS infusions. Analysis of the dose-response curves indicated approximately 10- and 5-fold greater potencies of SRIH and SMS, respectively, in inhibiting GH as compared to TSH secretion. These results quantify the effect of SRIH as an inhibitor of GH secretion and suggest that if SRIH has a physiological role in the inhibition of TSH secretion in man, it is limited to conditions associated with marked suppression of GH.

Adult↗

PubMed1988

Enhanced growth hormone (GH) responsiveness to GH-releasing hormone after dietary manipulation in obese and nonobese subjects.

Changes in plasma GH responses to GHRH (1 microgram/kg, iv) were assessed after dietary manipulations in obese and nonobese subjects to determine whether the impaired GH responsiveness to GHRH in obesity is the consequence of obesity per se or of altered food intake. The mean plasma GH response to GHRH in 10 obese subjects was significantly (P less than 0.05) higher after a 72-h fast than when they were eating their usual diet. Comparable increases were found when 6 of the subjects were studied after eating an 800 Cal/day diet for 6 weeks (P less than 0.05). Plasma glucose and insulin levels were lower and FFA levels higher after fasting, but not after the diet, compared to values on the usual diet. The mean plasma somatomedin-C (Sm-C) level was similar to that in nonobese subjects and was unaffected by dietary changes. The peak GH responses to GHRH before fasting were inversely correlated with plasma Sm-C levels (r = 0.64; P less than 0.05). Plasma GH responses to GHRH in normal weight subjects were also higher after fasting for 24 h (P less than 0.05) and 72 h (P less than 0.01) than after an overnight fast. Plasma glucose, insulin, and FFA changes were similar in the obese and normal weight subjects. Plasma Sm-C levels in the nonobese subjects were slightly lower after 72 h of fasting. We conclude that the increased plasma GH responsiveness to GHRH after fasting is not unique to obesity and is unlikely to reflect a reversal of the obesity-associated impairment of GH secretion. The increased plasma GH responsiveness to GHRH after as little as 24 h of fasting suggests that it is a consequence of acute nutrient deprivation rather than weight loss. The enhanced responses in obese subjects after 6 weeks of food restriction, in contrast, are probably a consequence of weight reduction.

Adult↗

PubMed1988

Discordant effects of insulin-hypoglycemia on growth hormone (GH)-releasing hormone-stimulated GH and thyrotropin (TSH)-releasing hormone-stimulated TSH secretion.

The hypothesis that insulin hypoglycemia-induced GH release is mediated by a decrease in hypothalamic somatostatin (SRIH) secretion was tested by investigating whether insulin administration enhanced the responses of SRIH-sensitive pituitary hormones to hypothalamic hormone stimulation. Eight normal men were given a combined iv injection of GHRH (1 microgram/kg) and TRH (0.3 microgram/kg) on two occasions, on one of which regular insulin (0.1 U/kg, iv) was given 30 min before GHRH-TRH administration. Insulin hypoglycemia augmented the maximal incremental (P less than 0.01) and integrated (P less than 0.025) plasma GH responses to GHRH. In contrast, plasma TSH responses to TRH were diminished by insulin (maximal increment, P less than 0.025; integrated response, P less than 0.05). TRH-stimulated PRL secretion was not altered by prior insulin administration. The enhancement of GH responsiveness to maximal GHRH stimulation indicates mediation by a non-GHRH pathway. However, the discordant decrease in TSH responsiveness to TRH argues against a reduction in hypothalamic SRIH secretion as a mechanism for the action of insulin.

Adult↗

PubMed1988

Medical management of acromegaly due to ectopic production of growth hormone-releasing hormone by a carcinoid tumor.

A 59-yr-old woman with a disseminated carcinoid tumor was evaluated for acromegaly. She had previously undergone a hypophysectomy for acromegaly and an enlarged pituitary, with a reduction in her serum GH levels from 100 to 4 micrograms/L. Recurrence of acromegalic symptoms 2 yr later was accompanied by elevated serum GH (16 micrograms/L) and insulin-like growth factor I (IGF-I; 528 micrograms/L) and plasma GHRH levels (12 micrograms/L; normal, less than 30 ng/L). Computed tomographic scan did not reveal pituitary enlargement. Metastatic carcinoid tissue in bone removed at biopsy contained GHRH (100 pg/mg tissue). High performance liquid chromatography of plasma GHRH revealed predominantly GHRH-(3-40)-OH, a biologically inactive GHRH metabolite, along with mature GHRH forms, while carcinoid tissue contained both GHRH-(1-40)-OH and GHRH-(1-44)-NH2. Treatment with pergolide initially resulted in reduction in serum GH and IGF-I levels and amelioration of symptoms of acromegaly. However, after 14 months of pergolide therapy, serum GH levels increased despite administration of up to 1000 micrograms pergolide/day. Plasma GHRH levels remained elevated throughout the treatment period. Subsequent treatment with SMS 201-995, a long-acting somatostatin analog, for over 1 yr resulted in sustained reductions of ectopic GHRH secretion, GH hypersecretion, and IGF-I levels. Plasma GHRH levels correlated with simultaneously measured serum GH levels in response to acute SMS 201-995 administration. SMS 201-995 was an effective medical treatment for acromegaly caused by ectopic GHRH production in this patient.

Acromegaly↗

PubMed1988

Comparison of the sensitivity of growth hormone secretion to somatostatin in vivo and in vitro in acromegaly.

Somatostatin (SRIH) sensitivity in acromegaly was evaluated in vivo by comparing the inhibition of GHRH (1 microgram/kg, iv)-stimulated GH secretion in eight acromegalic and six normal subjects. A SRIH infusion (50 micrograms/h) that inhibited the mean plasma GH response to GHRH by 74 +/- 5% (+/- SE) in normal subjects had no significant effect in the acromegalic patients. However, when two acromegalic patients in whom SRIH had no suppressive effect were excluded from the analysis, the effect of SRIH in the other six (82 +/- 7%) was comparable to that in the normal subjects. Within the acromegalic group, the percent suppression of basal and GHRH-stimulated GH secretion was inversely correlated with both basal plasma GH (r = -0.751; P = 0.03 and r = -0.727; P = 0.04, respectively) and insulin-like growth factor I (r = -0.800; P = 0.02 and r = -0.727; P = 0.04, respectively) concentrations. The in vitro sensitivity to SRIH was studied in pituitary adenomas from five of the acromegalic patients in 3- to 4-day monolayer cultures of dispersed cells. The SRIH IC50 values were lowest in the tumors (8.6-44 pmol/L) from the three patients who had in vivo SRIH sensitivity (suppression of GHRH-stimulated GH secretion) comparable to that in the normal subjects. The IC50 values were higher in the tumors (150 and 21,000 pmol/L) from the two patients that were least responsive to SRIH in vivo. These results indicate that there is considerable variability of SRIH sensitivity in patients with acromegaly. Although the role of this defect in the pathogenesis of acromegaly is uncertain, it may be an important determinant in the degree of elevation of plasma GH levels.

Acromegaly↗

PubMed1988

Feedback regulation of growth hormone (GH)-releasing hormone gene expression by GH in rat hypothalamus.

The role of the pituitary, and in particular, of GH in GH-releasing hormone (GRH) gene expression was studied in hypophysectomized rats with and without GH treatment. Hypothalamic GRH mRNA was 6-fold greater in hypophysectomized than in control rats. Increased levels of GRH mRNA were observed at 3 days and the maximal increase was noted at 7 days, postoperatively. Administration of GH to hypox rats partially reversed the increase in GRH mRNA, suggesting a negative feedback regulation by GH of GRH gene activity at the transcript accumulation level. The overall regulation of GRH gene expression, however, appears more complex since GRH mRNA levels and GRH content exhibited discordant changes after both hypophysectomy and GH treatment, suggesting that factors other than GH are required for efficient translation of GRH mRNA.

Animals↗

PubMed1987

Ontogenesis of peptide-histidine-isoleucine (PHI)-containing neurons in the suprachiasmatic nucleus (SCN) of the rat.

The morphologic and ontogenetic changes in PHI (peptide-histidine-isoleucine)-containing neurons in the suprachiasmatic nucleus (SCN) of the rat were studied using immunohistochemistry. PHI immunoreactivity first appeared in neural perikarya and processes as early as day 18 of gestation, long before they became evident (day 10 postnatally) in other brain structures. PHI neurons in the SCN were initially small and exhibited faint staining. They gradually increased in number during fetal life, and were found throughout this nucleus by day 21. After birth, they rapidly increased in number and staining intensity. In the 20-day-old rat. PHI-containing perikarya were concentrated in the ventral and medial aspects of the SCN while fibers were located primarily within the dorsal and caudal portions, as in the adult rat. These findings suggest that PHI exerts a physiological role in the developing SCN.

Animals↗

PubMed1987

Intravenous medroxalol stimulates prolactin secretion in normal and hypertensive subjects.

This study evaluated the effects of medroxalol on prolactin secretion. Twelve normal subjects received medroxalol, 1 mg/kg, intravenously and on a separate occasion, 5% dextrose in water. Integrated prolactin secretion during the 3 hours after medroxalol injection was significantly increased as compared with dextrose (P less than 0.001). Intravenous administration of medroxalol, 2 mg/kg, to 10 hypertensive subjects resulted in significant elevation of mean prolactin levels above basal levels at all time intervals measured from 30 to 240 minutes after injection. Oral medroxalol administration to 11 hypertensive subjects for up to 15 months did not alter mean prolactin levels. Medroxalol neither stimulated prolactin release nor decreased dopamine suppression of prolactin release from pituitary cell cultures. In conclusion, intravenous medroxalol stimulates prolactin secretion in both normal and hypertensive subjects. This effect is not likely mediated by a direct action of the drug on the pituitary but rather by an effect either within the central nervous system or of a drug metabolite.

Adult↗

PubMed1987

Neuroanatomic localization of the inhibitory effect of TRH on growth hormone secretion.

The inhibitory effect of centrally administered thyrotropin-releasing hormone (TRH) on the plasma growth hormone (GH) response to GH-releasing hormone (GHRH) in the rat was studied in relation to the anatomic loci involved. Experiments were performed in animals with bilateral electrolytic lesions in the medial preoptic (MPO) area or with anterolateral hypothalamic deafferentation and in sham-operated controls. Blood samples were obtained every 10 to 20 min from and drugs were injected into freely moving animals with indwelling cannulas in the right atrium and lateral cerebral ventricle. In control animals, the plasma GH response to GHRH, 1 microgram iv, was almost completely inhibited by TRH, 1 microgram icv, injected 5 min previously. In animals with either MPO lesions or anterolateral hypothalamic deafferentation in which median eminence somatostatin immunochemical staining was almost completely eliminated, the GH response to GHRH was enhanced and TRH did not exhibit any inhibitory effect. These results, together with the previous observation that the inhibitory effect of TRH is blocked by prior treatment with anti-somatostatin serum, suggest that the effect of TRH is mediated by stimulation of somatostatin-containing neurons in the periventricular nucleus of the MPO area.

Afferent Pathways↗

PubMed1987

Pre- and postnatal developmental changes in hypothalamic content of rat growth hormone-releasing factor.

The ontogenesis of hypothalamic GH-releasing factor (GRF) in pre- and postnatal rats was examined by means of a specific rat GRF RIA. Whereas GRF content was undetectable (less than 10 pg/hypothalamus) on day 17 of gestation, it increased to 30-65 pg/hypothalamus during days 18-20. During postnatal life, hypothalamic GRF content increased more rapidly during days 20-50 than during days 0-20 or 50-90. GRF content was 900-1300 pg/hypothalamus in 50- to 90-day-old rats, and there was no consistent sex difference during postnatal life. Hypothalamic somatostatin levels, as measured by RIA, showed a developmental pattern similar to that of rat GRF. GRF immunoreactivity in hypothalamic extracts from fetal as well as adult rats exhibited HPLC retention times identical to that of synthetic rat GRF. Administration of antirat GRF serum produced a significant decrease in plasma GH levels in fetal rats on day 21 of gestation and in newborn pups 4 h after birth. Passive immunization against GRF caused a more marked suppression of plasma GH (75-85%) 6-9 h after birth and on postnatal day 3. The results demonstrate that immunoreactive GRF is present in measurable levels in the hypothalami of fetal and newborn rats, is chemically indistinguishable from synthetic rat GRF, and exhibits biological effects as early as day 21 of fetal life.

Aging↗

PubMed1987

Effect of hypophysectomy on hypothalamic growth hormone-releasing factor content and release in the rat.

The possible regulation of hypothalamic GH-releasing factor (GRF) by GH was studied in untreated and GH-treated hypophysectomized rats by measurement of rat hypothalamic GRF content and release in vitro with a specific GRF RIA. Two weeks after hypophysectomy, animals not receiving hormone replacement showed a marked reduction in hypothalamic GRF content (to 28% of sham-operated control values; P less than 0.001). Replacement therapy with T4, cortisone, and testosterone for 9 days did not correct the decrease in hypothalamic GRF content in hypophysectomized rats, though the addition of GH therapy partially restored GRF levels (to 55% of control values; P less than 0.001). GRF release from incubated mediobasal hypothalamic fragments of hypophysectomized rats was decreased both basally and in response to 30 mM K+. This defect was completely corrected by prior GH treatment. The results suggest an impairment of GRF synthesis and release in the presence of GH deficiency.

Animals↗