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At least 721 records · Page 40Linked to original sources
PubMed1994

Body changes in adolescent patients with growth hormone receptor deficiency receiving recombinant human insulin-like growth factor I and luteinizing hormone-releasing hormone analogue: preliminary results.

Auxological and body composition changes were studied in three adolescent patients (2 female, 1 male) with growth hormone receptor deficiency (GHRD) given insulin-like growth factor I (IGF-I), 120 micrograms/kg s.c. twice daily, plus a monthly intramuscular injection of 7.5 mg of a luteinizing hormone-releasing hormone (LHRH) analogue. Preliminary results from the first 12 months of the study show that height velocity was increased compared with the pretreatment values. This increase was probably due to the IGF-I therapy, as the LHRH analogue would have suppressed gonadotrophins and gonadal steroid production. There was a reduction in percentage body fat, and increases in lean mass and the lean:fat ratio, whole body mineral content and body calcium content, even when expressed per kg body weight. There was also a trend towards increased bone mineral density of the whole skeleton, lumbar spine and femoral structures, as well as a maturation of facial features. These preliminary results indicate that concomitant therapy with IGF-I and an LHRH analogue is safe and efficacious in inducing growth without advancing bone age in patients with GHRD.

Adolescent↗
PubMed1975

Growth hormone release inhibiting hormone: actions on thyrotrophin and prolactin secretion after thyrotrophinreleasing hormone.

The hypothalamic tetradecapeptide growth hormone release inhibiting hormone (GH-RIH) blocked the thyrotrophin response to thyrotrophin-releasing hormone (TRH) in normal people and in patients with primary hypothyroidism. This inhibition was dose related. The TRH-induced prolactin release was not affected by GH-RIH. This dissociation of the thyrotrophin and prolactin responses to TRH by GH-RIH suggests that there are different mechanisms for release of thyrotrophin and prolactin and that only the former is affected by GH-RIH.

Adult↗
PubMed1991

Prenatal hormone treatment with thyrotropin releasing hormone and with thyrotropin releasing hormone plus dexamethasone delays antioxidant enzyme maturation but does not inhibit a protective antioxidant enzyme response to hyperoxia in newborn rat lung.

Whereas glucocorticoid administration to pregnant rats produces parallel acceleration of lung surfactant and antioxidant enzyme system maturation in late gestation, prenatal thyroid hormone treatment results in acceleration of surfactant maturation, with a paradoxical decrease in antioxidant enzyme (AOE) development. In these studies, we tested whether prenatal thyroid releasing hormone (TRH) treatment would act like prenatal thyroid hormone on pulmonary surfactant and AOE system maturation and whether combined prenatal treatment with TRH plus dexamethasone (DEX) would alter these effects. Secondly, we tested whether prenatal TRH and prenatal TRH plus DEX would inhibit the ability of newborn rats to respond to hyperoxia with protective increases in AOE activities. Results of the developmental studies revealed significantly increased fetal lung disaturated phosphatidylcholine content with significantly decreased pulmonary AOE activities as a result of prenatal TRH treatment that was not reversed with the addition of DEX. Combined TRH plus DEX treatment resulted in statistically significant decreases in body weight, lung weight, and lung weight to body weight ratios at both 21 and 22 d of gestation; growth effects were not seen with TRH alone. In terms of hyperoxic AOE response, despite being born with lower baseline AOE levels, the newborn animals prenatally treated with TRH or TRH plus DEX were able to induce a normal pulmonary AOE response to high O2 exposure. Although requiring further investigation, this reassuring finding suggests that clinical prenatal therapy with TRH or the combination of TRH plus DEX is not contraindicated for those infants delivered prematurely who go on to require intensive hyperoxic therapy.

Animals↗
PubMed2003

Specificity of cognate ligand-receptor interactions: fusion proteins of human chorionic gonadotropin and the heptahelical receptors for human luteinizing hormone, thyroid-stimulating hormone, and follicle-stimulating hormone.

The family of glycoprotein hormones and their homologous heptahelical receptors represent an excellent system for comparative structure-function studies. We have engineered single chain molecules of human chorionic gonadotropin (hCG) fused to its cognate receptor, LH receptor (LHR), and to the noncognate receptors, TSH receptor (TSHR) and FSH receptor (FSHR; N-beta-alpha-receptor-C), to create the yoked (Y) complexes YCG/LHR, YCG/TSHR, and YCG/FSHR. The expression and bioactivity of these fusion proteins were examined in transiently transfected HEK 293 cells. Western blot analysis and antibody binding assays demonstrated that each of the proteins was expressed. In the case of YCG/LHR, minimal binding of exogenous hormone was observed due to the continued occupation of receptor by the fused ligand. The presence of hCG in the YCG/TSHR and YCG/FSHR, however, did not prevent binding of exogenous cognate ligand, presumably due to the lower affinity of hCG. The basal cAMP levels in cells expressing the YCG/LHR complex was approximately 20-fold higher than that in cells expressing LHR. Increases in basal cAMP production were also observed with YCG/TSHR and YCG/FSHR, e.g. 13- and 4-fold increases, respectively. Whereas the affinity and specificity of hCG for LHR are extraordinarily high, the hormone is capable of binding to and activating both TSHR and FSHR under these conditions that mimic high ligand concentrations. These findings were confirmed by adding high concentrations of hCG to cells expressing TSHR and FSHR. Although the functional interaction of hCG and TSHR has been recognized in gestational hyperthyroidism, there are no reports linking hCG to FSHR activation. This study, however, suggests that such a functional interaction is capable of occurring under conditions of high circulating levels of hCG, e.g. the first trimester of pregnancy and in patients with hCG-secreting tumors.

Amino Acid Sequence↗
PubMed1990

Growth hormone (GH) regulation of cytochrome P-450IIC12, insulin-like growth factor-I (IGF-I), and GH receptor messenger RNA expression in primary rat hepatocytes: a hormonal interplay with insulin, IGF-I, and thyroid hormone.

We have studied the GH-dependent expression of cytochrome P-450IIC12 (P-450(15)beta) mRNA and insulin-like growth factor-I (IGF-I) mRNA in primary adult rat hepatocytes. The GH receptor (GHR), being the common denominator for the GH response, was also studied. The respective mRNA levels were measured with specific solution hybridization assays. By investigating the effects of insulin, IGF-I, T3, and corticosterone, alone or in combinations, in the presence or absence of GH we concluded that GH is indeed the inducer of P-450(15)beta mRNA and IGF-I mRNA. However, insulin and IGF-I exerted a 2-fold potentiation of the GH-induced expression of the P-450(15)beta and IGF-I mRNA species. No significant effect of insulin was observed on GHR mRNA expression, but a translational or posttranslational effect on GHR was seen, in that insulin increased the binding of GH to the cells 4-fold. Furthermore, T3 caused a 9-fold increase in the GH-induced expression of IGF-I mRNA. These observations led us to postulate a possible mechanism of hormonal interplay between GH, thyroid hormone, and IGF-I in vivo, i.e. a thyroid hormone potentiation of the GH-induced IGF-I expression, which, in turn, leads to an increased GHR level and thereby a potentiation of the GH-induced expression of P-450(15)beta and, at least transiently, of IGF-I. A transcriptional mechanism of GH action on P-450(15)beta and IGF-I mRNA induction was indicated by the similar half-lives of respective mRNAs in the presence or absence of GH in cell cultures treated with actinomycin-D.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Resting metabolic rate, body composition and related hormonal parameters in growth hormone-deficient adults before and after growth hormone replacement therapy.

The resting metabolic rate (RMR), and body composition were assessed in 30 growth hormone-deficient (GHD) adults before and after 3 and 6 months of replacement therapy with recombinant human growth hormone (rhGH). In addition, insulin-like growth factor I (IGF-I), IGF binding proteins (IGFBPs) and plasma insulin were measured at baseline and at 6 months in relation to RMR. During 6 months of rhGH replacement therapy, body fat decreased from 18.2 +/- 1.5 (mean +/- SEM) to 14.3 +/- 1.6 kg (p < 0.0001), whereas fat-free mass (FFM) increased from 53.5 +/- 3.3 to 56.3 +/- 3.6 kg (p < 0.0001), RMR increased from 1246 +/- 92 to 1539 +/- 102 kcal/24 h (p < 0.0001) and RMR per kilogram of FFM increased from 23.2 +/- 0.6 to 27.4 +/- 0.5 (p < 0.0001). When RMR data were adjusted for the differences in FFM, it appeared that apart from the increase in FFM, other factors may play a role in the increase in RMR. During rhGH replacement therapy, IGF-I (p < 0.0001) and IGFBP-3 (p = 0.003) levels increased, whereas IGFBP-1 levels decreased significantly (p = 0.004). The FFM explained for about 80% of the variance in RMR. In addition, waist/hip ratio and plasma IGF-I contributed significantly to the explained variance of RMR. This study shows that in GHD adults FFM is the main determinant of RMR and that, next to the increase in FFM, changes in metabolic and hormonal parameters contribute to the increase in RMR during rhGH replacement therapy.

Adult↗
PubMed1993

Monoclonal antibodies to bovine growth hormone potentiate hormonal activity in vivo by enhancing growth hormone binding to hepatic somatogenic receptors.

Administration of GH complexed with monoclonal antibodies (MABs) potentiates the in vivo actions of the hormone. In particular, growth and serum IGF-I concentrations of GH-treated hypophysectomized rats are increased by concomitant injection of anti-GH MABs. Among 37 anti-bovine GH (bGH) MABs, we selected one MAB with the most potentiating effects to investigate the mechanisms responsible for this phenomenon. Hypophysectomized rats were killed 18 h after a single s.c. injection of bGH (100 micrograms/rat), alone or complexed with increasing doses of MAB (4, 40, 400 micrograms/rat; MAB:bGH molar ratio: 0.005, 0.05, 0.5). IGF-I was measured by radioimmunoassay in acid-extracted sera and livers, whereas liver IGF-I mRNA was quantified by Northern blot hybridization. The in vivo occupancy of liver somatogenic (GH) receptors was derived from the determinations of total and free 125I-labelled bGH binding to liver homogenates treated with 4 mol MgCl2/l or water. Injection of MAB-bGH complexes enhanced body weight gain and raised serum IGF-I, liver IGF-I and liver IGF-I mRNA more than bGH alone (1.6-, 6-, 10- and 7-fold increases at the highest dose of MAB, compared with bGH alone; P < 0.001). These potentiating effects of the MAB were dose-dependent and significant potentiation of the growth response was already observed with the lowest dose of MAB. In vivo occupancy of liver GH receptors was markedly higher 18 h after injection of MAB-bGH complexes than after bGH alone, and this effect was also dose-dependent (receptor occupancy of 28%, 37% and 83% after 4, 40 and 400 micrograms of MAB respectively compared with 6% after bGH alone; P < 0.05, 0.05 and 0.001 respectively). In contrast, the in vitro binding of 125I-labelled bGH to liver homogenates was decreased in the presence of high doses of MAB. We conclude that low amounts of MABs complexed with bGH potentiate the stimulation by the hormone of liver IGF-I synthesis and secretion in a dose-dependent manner. These effects are mediated, at least in part, through changes in hormone-receptor interaction in vivo, leading to enhanced and/or prolonged binding of bGH to its somatogenic receptors.

Animals↗
PubMed1992

Luteinizing hormone-releasing hormone receptor bindings of the hen pituitary: difference between laying and nonlaying hens, effects of ovarian steroid hormones in vivo, and changes during an ovulatory cycle.

The equilibrium dissociation constant (Kd) of the pituitary luteinizing hormone-releasing hormone (LHRH) receptors and the maximum binding capacity (Bmax) per milligram of membrane protein were greater in laying hens than in nonlaying hens. A single i.m. injection of progesterone, estradiol-17 beta, or 5 alpha-dihydrotestosterone into nonlaying hens caused an increase in Kd and Bmax values. During an ovulatory cycle of the laying hen, Kd and Bmax values decreased from 16 to 14 h and 8 to 6 h before ovulation. A decrease in the Bmax value was also found 24 to 21 h before ovulation. A single i.v. injection of chicken LHRH-I caused a decrease in the Kd and Bmax values within 2 min after the injection. The results suggest that the hen pituitary LHRH receptor bindings are affected by ovarian steroid hormones and that their changes during the ovulatory cycle may relate to the release of a gonadotropin from the pituitary.

Animals↗
PubMed2000

alpha-Melanocyte-stimulating hormone is contained in nerve terminals innervating thyrotropin-releasing hormone-synthesizing neurons in the hypothalamic paraventricular nucleus and prevents fasting-induced suppression of prothyrotropin-releasing hormone gene expression.

The hypothalamic arcuate nucleus has an essential role in mediating the homeostatic responses of the thyroid axis to fasting by altering the sensitivity of prothyrotropin-releasing hormone (pro-TRH) gene expression in the paraventricular nucleus (PVN) to feedback regulation by thyroid hormone. Because agouti-related protein (AGRP), a leptin-regulated, arcuate nucleus-derived peptide with alpha-MSH antagonist activity, is contained in axon terminals that terminate on TRH neurons in the PVN, we raised the possibility that alpha-MSH may also participate in the mechanism by which leptin influences pro-TRH gene expression. By double-labeling immunocytochemistry, alpha-MSH-IR axon varicosities were juxtaposed to approximately 70% of pro-TRH neurons in the anterior and periventricular parvocellular subdivisions of the PVN and to 34% of pro-TRH neurons in the medial parvocellular subdivision, establishing synaptic contacts both on the cell soma and dendrites. All pro-TRH neurons receiving contacts by alpha-MSH-containing fibers also were innervated by axons containing AGRP. The intracerebroventricular infusion of 300 ng of alpha-MSH every 6 hr for 3 d prevented fasting-induced suppression of pro-TRH in the PVN but had no effect on AGRP mRNA in the arcuate nucleus. alpha-MSH also increased circulating levels of free thyroxine (T4) 2.5-fold over the levels in fasted controls, but free T4 did not reach the levels in fed controls. These data suggest that alpha-MSH has an important role in the activation of pro-TRH gene expression in hypophysiotropic neurons via either a mono- and/or multisynaptic pathway to the PVN, but factors in addition to alpha-MSH also contribute to the mechanism by which leptin administration restores thyroid hormone levels to normal in fasted animals.

Animals↗
PubMed1987

Influence of hormonal imprinting on hormone level. Permanent receptor damaging effect of pituitary hormones administered to newly-hatched cockerels.

The overlapping effect of TSH and FSH on the gonad and on the thyroid gland can be demonstrated in cockerels even at the age of five weeks. These hormones influence the secretion of testosterone in a similar way and to a similar extent, while on the thyroxine level the influence of the specific hormone is more pronounced. Neonatal FSH and TSH treatment considerably decreased the basal testosterone level measured at the age of five weeks. Neonatal FSH treatment increased the basal T4 level while TSH treatment decreased it. The effect of TSH treatment administered at the age of five weeks in increasing the testosterone level was weakened after neonatal pretreatment with any iodine hormone. The effect of TSH treatment could only be inhibited by neonatal FSH pretreatment. Neonatal pretreatment with any of the trophormones caused a diminution of the T4 level augmenting of FSH and TSH administered at the age of five weeks.

Animals↗
PubMed1995

Growth hormone regulation of male-specific rat liver P450s 2A2 and 3A2: induction by intermittent growth hormone pulses in male but not female rats rendered growth hormone deficient by neonatal monosodium glutamate.

Growth hormone (GH) secretory patterns regulate the expression of several sex-dependent liver cytochrome P450 (CYP) genes. Studies using the hypophysectomized rat model have established that the intermittent plasma GH secretory pattern associated with adult male rats markedly stimulates liver expression of the male-specific CYP 2C11, a testosterone 2 alpha- and 16 alpha-hydroxylase, but is not required for expression of other male-specific liver enzymes, including CYP 2A2, a testosterone 15 alpha-hydroxylase, and CYP 3A2, a testosterone 6 beta-hydroxylase. In the present study, the effects of intermittent GH treatment on liver CYP expression were studied in adult rats rendered GH deficient by neonatal administration of monosodium glutamate (MSG), which depletes circulating adult GH without the global loss of other pituitary-dependent hormones that is associated with hypophysectomy. Restoration of the normal masculine circulating GH profile of six daily pulses (180-225 ng GH/ml/peak) in MSG-treated male rats by the use of an external pumping apparatus led to a substantial (30-50%) restoration of normal male levels of CYP 2A2 and CYP 3A2 activity, protein, and mRNA. GH pulsation at the nonphysiological frequencies of two or four times per day was less effective unless given at a dose that resulted in supraphysiological plasma GH levels. Although intermittent GH treatment can induce male-specific P450 expression in hypophysectomized female rats, the same hormone treatment did not stimulate CYP 2A2 or CYP 3A2 expression in MSG-treated female rats. Liver GH receptor mRNA levels at adulthood were not significantly altered by neonatal MSG treatment, suggesting that the unresponsiveness of MSG-treated females and the previously reported low responsiveness of MSG-treated males to GH-induced CYP 2C11 expression are not due to the absence of GH receptor. Moreover, normal liver IGF-1 mRNA levels were expressed in the MSG-treated female rats, suggesting that the liver GH receptor is functional in these animals. The present findings establish that the adult male-specific enzymes CYP 2A2 and CYP 3A2 can be positively regulated by intermittent GH pulsation despite their GH-independent expression in hypophysectomized rats. Moreover, neonatal MSG treatment, particularly in female rats, may lead to the loss of factors other than GH that are required for full expression of the pulsatile GH-stimulated CYP 2A2, 3A2, and 2C11 genes.

Animals↗
PubMed1994

3,5,3'-L-triiodothyronine (thyroid hormone)-induced protein-DNA interactions in the thyroid hormone response elements and cell type-specific elements of the rat growth hormone gene revealed by in vivo dimethyl sulfate footprinting.

The cell type-specific element and 3,5,3'-L-triiodothyronine (thyroid hormone) (T3) response element of the rat growth hormone gene act synergistically to produce cell type-specific, T3-regulated expression. Pit-1 is a pituitary cell type-specific transcription factor that binds the cell type-specific element and is essential to its activity. T3 receptors bind as homodimers and heterodimers to the T3 response element and are essential for its activity. Here, we report the use of ligation-mediated polymerase chain reaction in vivo dimethyl sulfate footprinting to study the effects of T3 on protein-DNA interactions in the rat growth hormone gene promoter in vivo. T3-responsive guanine methylation was detected only in and near the T3 response element and the Pit-1 binding sites. The results indicate that within 2 h, T3 induces occupancy of the T3 response element and Pit-1 sites by their respective trans-acting factors in vivo.

Animals↗
PubMed1990

A new test for the diagnosis of growth hormone deficiency due to primary pituitary impairment: combined administration of pyridostigmine and growth hormone-releasing hormone.

The diagnosis of growth hormone (GH) deficiency (GHD) is currently based on failure to increase plasma GH levels to an arbitrary cutoff point of 7 or 10 micrograms/l in response to two provocative stimuli. False negative responses to these tests, however, frequently occur thus reducing their diagnostic reliability. The aim of this study was to assess a combination of pyridostigmine (PD) and GH-releasing hormone (GHRH) (60 mg oral PD 60 min before 1 microgram/Kg GHRH iv) as a reliable test probing pituitary somatotropic function. In fact PD, an acetylcholinesterase inhibitor, strikingly potentiates GH response to GHRH likely by inhibiting somatostatin release. The combination PD + GHRH was tested in normal children and adolescents (NS, n = 27) and in a large group of short children classified as having familial short stature (FSS, n = 24), constitutional growth delay (CGD, n = 34) and GH deficiency (organic, oGHD, n = 6; idiopathic, iGHD, n = 10). In all groups results obtained by PD + GHRH were compared with those obtained by testing with GHRH, clonidine (CLON) and PD alone and by studying spontaneous nocturnal GH secretion over 8 hours. Assuming 7 micrograms/l as minimum normal GH peak, a positive response occurred in only 18/24, 11/12 and 12/13 NS for GHRH, CLON, and PD, respectively. In contrast even assuming a minimum normal GH peak as high as 20 micrograms/l, PD + GHRH induced a positive response in 27/27 NS all having a nocturnal GH mean concentration (MC) greater than or equal to 3 micrograms/l. Therefore PD + GHRH test gave no false negative responses and this was true not only in NS but even in all FSS and CGD having a GH MC greater than or equal to 3 micrograms/l. On the other hand, PD + GHRH induced a negative GH response in all oGHD and in 8/10 iGHD patients. In the remaining two iGHD patients, PD + GHRH demonstrated a normal pituitary GH reserve in spite of a GH MC less than 3 micrograms/l and low IGF-I level, thus pointing to a hypothalamic pathogenesis for the GHD. Considering FSS and CGD children having a GH MC less than 3 micrograms/l, PD + GHRH showed a primary pituitary GH deficiency in 3/12 CGD with low plasma IGF-I levels. In conclusion, in slowly growing children PD + GHRH test is the most reliable provocative test for the diagnosis of primary pituitary GH deficiency being capable to discriminate between an unequivocally normal and impaired somatotropic function.(ABSTRACT TRUNCATED AT 400 WORDS)

Administration, Oral↗
PubMed1991

The growth hormone response to pyridostigmine plus growth hormone releasing hormone is not influenced by pubertal maturation.

We have evaluated the effect of pubertal maturation on the GH response to growth hormone releasing hormone (GHRH), pyridostigmine (PD) and the combined administration of PD + GHRH in a group of short normal children. Fifteen were prepubertal (13 boys and 2 girls, age 5.0 - 12.5 yr), 10 were early pubertal (8 boys and 2 girls, age 11.5 - 16.9 yr in Tanner stage 2-3 of pubertal maturation), and 6 were late pubertal (6 boys and 2 girls, age 13.6 - 17.1 yr in Tanner stage 4-5 of pubertal maturation). All subjects were tested on three occasions with GHRH 1-29 (1 microgram/Kg iv), PD (60 mg po) and PD + GHRH (60 mg PD administered orally 60 min before GHRH). Peak GH levels after GHRH, PD, and PD + GHRH in the prepubertal children (16.0 +/- 2.8, 8.1 +/- 1.3 and 51.1 +/- 5.5 ng/ml, mean +/- SE, respectively) were not different from those observed in the early pubertal (18.4 +/- 2.1, 9.1 +/- 1.9 and 41.2 +/- 5.6 ng/ml, respectively) and in the late pubertal group (14.9 +/- 2.3, 13.1 +/- 2.4 and 42.6 +/- 2.9 ng/ml, respectively). Evaluation of the area under the curve (AUC) also showed no difference in the GH response to GHRH, PD and PD + GHRH between the three groups studied. These results confirm that the combination PD + GHRH is a powerful test to study the GH secretory capacity of the pituitary, and show that pubertal maturation has no effect on the GH response to this test.

Administration, Oral↗
PubMed1989

The effect of thyroid status on the growth hormone response to growth hormone releasing hormone 1-44.

The growth hormone (GH) response to iv injection of GH releasing hormone 1-44 (GHRH 1-44) has been examined in 10 hyperthyroid and 6 hypothyroid patients. Both groups of patients were studied at presentation and when euthyroid (mean 5 months for hyperthyroid, 8 months for hypothyroid). Hyperthyroid subjects demonstrated a peak mean (+/- SE) level of 17.7 +/- 3.8 mU/l, with an integrated GH 29.3 +/- 6.4 mU/l.h. When euthyroid the peak mean level was 17.0 +/- 5.0 mU/l and the integrated GH 22.8 +/- 4.2 mU/l.h. Neither change was statistically significant. Hypothyroid subjects had a peak mean level of 5.0 +/- 2.7 mU/l and integrated GH of 5.9 +/- 1.7 mU/l.h and when euthyroid a peak mean level of 7.1 +/- 4.8 mU/l and integrated GH of 8.1 +/- 3.6 mU/l.h. Body weight did not change significantly in this group of hypothyroid subjects with prolonged treatment. The increase in GH response to GHRH previously reported following replacement therapy may reflect a treatment-induced decrease in body weight, or may be a short term effect.

Adolescent↗
PubMed1995

Growth hormone response to growth hormone-releasing hormone and clonidine in depression.

Growth hormone (GH) responses to the alpha 2-adrenoceptor agonist clonidine and to GH-releasing hormone (GHRH) were measured in 12 patients fulfilling DSM-III-R criteria for major depressive disorder and in 12 age- and sex-matched controls. GH responses to clonidine correlated significantly with the GH responses to GHRH in the depressed patients as well as in the controls. Neither the responses to clonidine nor the responses to GHRH were significantly lower in depressed patients than in controls. Similarly, somatomedin-C (Sm-C) plasma concentrations and baseline GH concentrations were not different between the two groups. The data do not suggest that blunted GH responses to clonidine and/or GHRH represent specific features of depression.

Adrenergic alpha-Agonists↗
PubMed1992

Effects of passive immunization of growth hormone-releasing hormone and somatostatin on growth hormone secretion under conditions of high somatostatin tone.

Pulsatile GH secretion decreases during food-deprivation in the rat. It has been hypothesized that this decrease is due to elevated hypothalamic somatostatin secretion. This is based on the observation that GH increases in food-deprived rats following removal of endogenous somatostatin using passive immunization techniques. Cognizant of the important stimulatory effects of growth hormone-releasing hormone (GHRH) on GH secretion, we sought to determine if this neuropeptide plays any role in mediating GH secretion in food-deprived rats. Male rats were prepared with indwelling venous catheters using sodium pentobarbital anesthesia seven days prior to experimentation. Animals were food-deprived for 72 h, after which control blood samples were drawn from -60 to 0 min. One group was then treated with normal rabbit serum (NRS), while a second group was treated with GHRH antiserum (GHRHab). At 55 min all animals received somatostatin antiserum (SSab). No animal exhibited any spontaneous GH peak during the one hour control period or in the subsequent one hour period following the administration of GHRHab or NRS. Absence of GH pulsatility during food-deprivation, coupled with no decrease in GH levels in food-deprived rats treated with GHRHab suggest that diminished GHRH pulsatility is likely during food-deprivation. Subsequent treatment of these animals with SSab resulted in an identical 2.5 fold increase in GH concentrations. This result suggests that GHRH is not involved in the GH rebound following somatostatin withdrawal in food-deprived rats.

Animals↗
PubMed1989

Effect of dietary restriction and repeated growth hormone-releasing factor injections on growth hormone response to growth hormone-releasing factor in obese subjects.

The response of serum growth hormone (GH) to a test bolus of growth hormone-releasing factor (GRF) (1 micrograms/kg, IV) was examined in eight obese subjects (166% +/- 8% ideal body weight [IBW] during a weight-maintaining control period and after 2 weeks of hypocaloric feeding (750 kcal). During the period of hypocaloric feeding subjects received either repetitive GRF 1 micrograms/kg, IV (GRF group, n = 6) at 9 AM, 1 PM, and 5 PM three times a week, or saline injections (placebo group, n = 6) at the same intervals. Four subjects were studied twice, several months apart, each receiving GRF and placebo treatments. Nitrogen balance was determined daily throughout the study. We also examined GH response to the GRF test in seven normal-weight subjects (106% +/- 6% IBW]. During the control period, obese subjects demonstrated a blunted GH response to GRF expressed as peak height or GH area under the curve (0 to 120 minutes) compared with normal subjects (P less than .005). At the end of the hypocaloric feeding, mean GH peak height after the GRF test was unchanged in the placebo group compared with the control period. GH release was significantly increased only during the second hour of testing (P less than .025). However, the GRF group demonstrated an increase in both mean GH peak height (P less than .025) and GH release during the first and second hours of testing (P less than .025) compared with the control period. Weight loss and blood glucose, triglycerides, FFA, amino acids, insulin, and T3 changes were similar in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗