Maintenance of a normal meal-induced decrease in plasma ghrelin levels in children with Prader-Willi syndrome.

Ghrelin is a 28-amino acid peptide recently identified in the stomach as the endogenous ligand for the growth hormone secretagogue receptor (GHS-R1a). Ghrelin is a potent stimulator of GH secretion. It was recently shown that circulating ghrelin levels in humans rise shortly before and fall shortly after every meal, and that ghrelin administration increases voluntary food intake. The hypothesis that ghrelin hypersecretion might contribute to genetic obesity has never been investigated. In this context, Prader-Willi syndrome is the most common form of human syndromic obesity. As ghrelin affects appetite as well as GH secretion and both are abnormal in PWS, it has been surmised that these alterations might be due to ghrelin dysregulation. The aim of the study was to investigate whether ghrelin is suppressed by the meals differently in PWS children than in PWS adults. Overnight circulating fasting ghrelin levels and ghrelin levels 120 min after breakfast were assayed in 7 PWS children (10.2 +/- 1.7 yr), 7 subjects with morbid obesity (10.3 +/- 1.3 yr), and 5 normal controls (8.4 +/- 1.4 yr). Because of the data spread, no statistical difference was observed in fasting ghrelin levels between PWS and control children (p = NS); anyway, fasting ghrelin levels were significantly lower in obese children than in the other groups (p < 0.05 vs. control and PWS children). Ghrelin levels were slightly suppressed by the meal in control subjects (mean fasting ghrelin: 160.2 +/- 82 pg/ml; after the meal, 141.2 +/- 57 pg/ml, p = NS); the meal failed to suppress ghrelin levels in obese children (mean fasting ghrelin: 126.4 +/- 8.5 pg/ml; after the meal, 119.1 +/- 8.3 pg/ml, p = NS). Interestingly, the meal markedly suppressed ghrelin levels in PWS children (mean fasting ghrelin: 229.5 +/- 70.4 pg/ml; after the meal, 155.8 +/- 34.2 pg/ml, p < 0.01). In conclusion, since a lack of decrease in circulating ghrelin induced by the meal was previously reported in PWS adults, the finding of a meal-induced decrease in ghrelin levels in our population of young PWS would imply that the regulation of the ghrelin system involved in the orexigenic effects of the peptide is operative during childhood, although it progressively deteriorates and is absent in adulthood when hyperphagia and obesity progressively worsen.     

Growth hormone and ghrelin secretion in severely obese women before and after bariatric surgery

Objective: The objective was to evaluate ghrelin and growth hormone (GH) interactions and responses to a growth hormone‐releasing hormone (GHRH)/arginine test in severe obesity before and after surgically‐induced weight loss. Research Methods and Procedures: Our study population included 11 severely obese women 39 ± 12 years of age, with a mean BMI of 48.6 ± 2.4 kg/m², re‐studied in a phase of stabilized body weight, with a BMI of 33.4 ± 1.2 kg/m², 18 months after having successfully undergone biliopancreatic diversion (BPD). A GHRH/arginine test was performed before and 18 months after BPD to evaluate ghrelin and GH interactions. Active ghrelin, measured by radioimmunoassay (RIA), and GH, measured by chemiluminescence assay, were assayed before and after the GHRH/arginine test. Results: Fasting serum GH levels and GH area under the curve (AUC) significantly increased from 0.2 ± 0.05 ng/mL to 1 ± 0.3 ng/mL (p < 0.05) and from 514.76 ± 98.7 ng/mL for 120 minutes to 1957.3 ± 665.1 ng/mL for 120 minutes after bariatric surgery (p < 0.05), respectively. Although no significant change in fasting ghrelin levels was observed (573 ± 77.9 before BPD vs. 574.1 ± 32.7 after BPD), ghrelin AUC significantly increased from ?3253.9 ± 2180.9 pg/mL for 120 minutes to 1142.3 ± 916.4 pg/mL for 120 minutes after BPD (p < 0.05). Fasting serum insulin‐like growth factor (IGF)‐1 concentration did not change significantly (133.6 ± 9.9 ng/mL before vs. 153.3 ± 25.2 ng/mL after BPD). Discussion: Our study demonstrates that the mechanisms involved in ghrelin and GH secretion after the secretagogue stimulus (GHRH/arginine) are consistent with patterns observed in other populations.     

Pyridostigmine enhances even if it does not normalize the growth hormone responses to growth hormone-releasing hormone in patients with Cushing's disease.

Subjects with Cushing's disease have diminished growth hormone (GH) response to growth hormone-releasing hormone (GHRH). The aim of our study was to investigate the underlying mechanism of this diminished GH response in these patients using pyridostigmine (PD), an acetylcholinesterase inhibitor, which is reported to increase GH secretion by reducing somatostatin tone. Eight subjects with untreated Cushing's disease (caused by a pituitary adenoma) and 6 control subjects received GHRH 100 micrograms in 1 ml of saline, as intravenous bolus injection 60 min after (1) placebo (2 tablets, p.o.) or (2) PD (120 mg, p.o.). After GHRH plus placebo, the GH peak (mean +/- SEM) was significantly lower in subjects with Cushing's disease (2.4 +/- 0.5 micrograms/l) compared to control subjects (25.1 +/- 1.8 micrograms/l, p less than 0.05). After GHRH plus PD, the GH peak was significantly enhanced both in subjects with Cushing's disease (7.1 +/- 2.3 micrograms/l, p less than 0.05) and in control subjects (42.3 +/- 4.3 micrograms/l, p less than 0.05). In patients with Cushing's disease, the GH response to GHRH plus PD was lower with respect to the GH response to GHRH alone in normal subjects. We conclude that hypercortisolism may cause a decrease in central cholinergic tone which is in turn hypothesized to be responsible of an enhanced somatostatin release from the hypothalamus. However, other metabolic or central nervous system alterations may act synergistically with hypercortisolism in causing GH inhibition in patients with Cushing's disease.     

Metabolic regulation of growth hormone by free fatty acids, somatostatin, and ghrelin in HIV-lipodystrophy

Human immunodeficiency virus (HIV)-lipodystrophy is a syndrome characterized by changes in fat distribution and insulin resistance. Prior studies suggest markedly reduced growth hormone (GH) levels in association with excess visceral adiposity among patients with HIV-lipodystrophy. We investigated mechanisms of altered GH secretion in a population of 13 male HIV-infected patients with evidence of fat redistribution, compared with 10 HIV-nonlipodystrophic patients and 11 male healthy controls similar in age and body mass index (BMI). Although similar in BMI, the lipodystrophic group was characterized by increased visceral adiposity, free fatty acids (FFA), and insulin and reduced extremity fat. We investigated ghrelin and the effects of acute lowering of FFA by acipimox on GH responses to growth hormone-releasing hormone (GHRH). We also investigated somatostatin tone, comparing GH response to combined GHRH and arginine vs. GHRH alone with a subtraction algorithm. Our data demonstrate an equivalent number of GH pulses (4.1 +/- 0.6, 4.7 +/- 0.8, and 4.5 +/- 0.3 pulses/12 h in the HIV-lipodystrophic, HIV-nonlipodystrophic, and healthy control groups, respectively, P > 0.05) but markedly reduced GH secretion pulse area (1.14 +/- 0.27 vs. 4.67 +/- 1.24 ng.ml(-1).min, P < 0.05, HIV-lipodystrophic vs. HIV-nonlipodystrophic; 1.14 +/- 0.27 vs. 3.18 +/- 0.92 ng.ml(-1).min, P < 0.05 HIV-lipodystrophic vs. control), GH pulse area, and GH pulse width in the HIV-lipodystrophy patients compared with the control groups. Reduced ghrelin (418 +/- 46 vs. 514 +/- 37 pg/ml, P < 0.05, HIV-lipodystrophic vs. HIV-nonlipodystrophic; 418 +/- 46 vs. 546 +/- 45 pg/ml, P < 0.05, HIV-lipodystrophic vs. control), impaired GH response to GHRH by excess FFA, and increased somatostatin tone contribute to reduced GH secretion in patients with HIV-lipodystrophy. These data provide novel insight into the metabolic regulation of GH secretion in subjects with HIV-lipodystrophy.     

Nocturnal ghrelin pulsatility and response to growth hormone secretagogues in healthy men

The physiological importance of endogenous ghrelin in the regulation of growth hormone (GH) secretion is still unknown. To investigate the regulation of ghrelin secretion and pulsatility, we performed overnight ghrelin and GH sampling every 20 min for 12 h in eight healthy male subjects [age 37 +/- 5 (SD) years old, body mass index 27.2 +/- 2.9 kg/m2]. Simultaneous GH and ghrelin levels were assessed to determine the relatedness and synchronicity between these two hormones in the fasted state during the overnight period of maximal endogenous GH secretion. Pulsatility analyses were performed to determine simultaneous hormonal dynamics and investigate the relationship between GH and ghrelin by use of cross-approximate entropy (X-ApEn) analyses. Subjects demonstrated 3.0 +/- 2.1 ghrelin pulses/12 h and 3.3 +/- 0.9 GH pulses/12 h. The mean normalized ghrelin entropy (ApEn) was 0.93 +/- 0.09, indicating regularity in ghrelin hormone secretion. The mean normalized X-ApEn was significant between ghrelin and GH (0.89 +/- 0.12), demonstrating regularity in cosecretion. In addition, we investigated the ghrelin response to standard GH secretagogues [GH-releasing hormone (GHRH) alone and combined GHRH-arginine] in separate testing sequences separated by 1 wk. Our data demonstrate that, in contrast to GHRH alone, which had little effect on ghrelin, combined GHRH and arginine significantly stimulated ghrelin with a maximal peak at 120 min, representing a change of 66 +/- 14 pg/ml (P = 0.001 by repeated-measures ANOVA and P = 0.02 for GHRH vs. combined GHRH-arginine by MANOVA). We demonstrate relatedness between ghrelin and GH pulsatility, suggesting either that ghrelin participates in the pulsatile regulation of GH or that the two hormones are simultaneously coregulated, e.g., by somatostatin or other stimuli. Furthermore, the differential effects of GHRH alone vs. GHRH-arginine suggest that inhibition of somatostatin tone may increase ghrelin. These data provide further evidence of the physiological regulation of ghrelin in relationship to GH.     

GH responses to GHRH and GHRP-6 in Streptozotocin (STZ)-diabetic rats

GH responses to GHRH, the physiologic hypothalamic stimulus, and GHRP-6, a synthetic hexapeptide that binds the Ghrelin receptor, were studied in rats treated with streptozotocin (STZ), an experimental model of diabetes. Sprague-Dawley male rats received a single injection either of STZ (70 mg/Kg in 0.01 M SSC, i.p.) or of the vehicle (0.01 M SSC). GH responses were challenged with two different doses of GHRH (1 and 10 microg/kg) or GHRP-6 (3 and 30 microg/kg) and with a combination of both at low (1 + 3 microg/kg) or high (10 + 30 microg/kg) doses, respectively. We observed a dose-dependent effect for GH responses to GHRH both in STZ-treated rats and in controls. However, we could not find significant differences between STZ-rats and controls. GH responses to GHRP-6 occurred in a dose-dependent manner in STZ-rats, but not in controls. GH responses to GHRP-6 in both groups were clearly lower than those elicited by GHRH. GH responses to 30 microg/Kg of GHRP-6 were significantly greater in STZ-rats than in controls (AUC: 3549.9 +/- 1001.4 vs. 2046.4 +/- 711.7; p<0.05). The combined administration of GHRH plus GHRP-6 was the most potent stimuli for GH in both groups. The administration of doses in the lower range (1 + 3 microg/Kg, GHRH + GHRP-6 respectively) induced a great peak of GH in STZ-rats and in control rats, revealing a synergistic effect of GHRH and GHRP-6 in both groups. When the higher doses were administered (10 + 30 microg/kg), GH levels in time 5, and AUC were significantly higher in control rats. In addition, a negative correlation between WT (weight tendency) values and GH responses, represented as AUC, could be established in STZ-rats (r2=-0.566, p=0.004 for GHRH; r2=-0.412, p=0.028 for GHRP-6). Thus, the more negative the values of WT were, the more severe the metabolic alteration and, therefore, the higher the GH response to GHRH and GHRHP-6. In conclusion, our results do not support the existence of a functional hypothalamic hypertone of SS in diabetic rats, as GH responses were not usually reduced in STZ-rats, except when both secretagogues were administered together at the higher doses. Besides, GH responses to GHRH and GHRP-6 were inversely correlated with the severity of the metabolic alteration in STZ-rats, meaning that worse glycaemic control promoted higher GH secretion. These results resemble those found in humans, where GH responses to secretagogues are increased in type-1 diabetes and depend on hyperglycaemia, and are representative of not well-controlled insulin-dependent diabetic status.     

Effects of GH on urea,glucose and lipid metabolism,and insulin sensitivity during fasting in GH-deficient patients

Fasting-related states of distress pose major health problems, and growth hormone (GH) plays a key role in this context. The present study was designed to assess the effects of GH on substrate metabolism and insulin sensitivity during short-term fasting. Six GH-deficient adults underwent 42.5 h of fasting on two occasions, with and without concomitant GH replacement. Palmitate and urea fluxes were measured with the steady-state isotope dilution technique after infusion of [9,10-3H]palmitate and [13C]urea. During fasting with GH replacement, palmitate concentrations and fluxes increased by 50% [palmitate: 378 +/- 42 (GH) vs. 244 +/- 12 micromol/l, P < 0.05; palmitate: 412 +/- 58 (GH) vs. 276 +/- 42 microM, P = 0.05], and urea turnover and excretion decreased by 30-35% [urea rate of appearance: 336 +/- 22 (GH) vs. 439 +/- 43 micromol. kg-1. h-1, P < 0.01; urea excretion: 445 +/- 43 (GH) vs. 602 +/- 74 mmol/24 h, P < 0.05]. Insulin sensitivity (determined by a euglycemic hyperinsulinemic clamp) was significantly decreased [M value: 1.26 +/- 0.06 (GH) vs. 2.07 +/- 0.22 mg. kg-1. min-1, P < 0.01] during fasting with GH replacement. In conclusion, continued GH replacement during fasting in GH-deficient adults decreases insulin sensitivity, increases lipid utilization, and conserves protein.     

Plasma growth hormone releasing factor levels in children: physiological and pharmacologically induced variations

Plasma growth hormone releasing factor (GHRH) was measured by RIA in the plasma of 41 children with constitutionally short stature. Basal plasma GHRH was 51 +/- 10 pg/ml. L-Dopa induced a 2-fold increase in circulating GHRH 30-45 min before the elevation of GH. A positive correlation (p less than 0.005) was found between the peak of GH and GHRH during the dopaminergic stimulus. On the opposite, the secretion of GH induced by amino acids or clonidine is not preceded by an elevation of plasma GHRH. When a release of GH appeared after the insertion of the venous catheter alone, probably due to the stress, it was preceded by a rise of plasma GHRH. In four sleeping adolescents during the night no relationship was found between the peaks of plasma GHRH and the peaks of GH secretion. These results suggest that the various stimulations of GH secretion used for investigations of a short stature do not act in the same way at the hypothalamo-pituitary level.     

Effect of arginine on the GHRH-stimulated GH secretion in patients with hyperthyroidism.

Patients with hyperthyroidism have reduced GH responses to pharmacological stimuli and reduced spontaneous nocturnal GH secretion. The stimulatory effect of arginine on GH secretion has been suggested to depend on a decrease in hypothalamic somatostatin tone. The aim of our study was to evaluate the effects of arginine on the GH-releasing hormone (GHRH)-stimulated GH secretion in patients with hyperthyroidism. Six hyperthyroid patients with recent diagnosis of Graves' disease [mean age +/- SEM, 39.2 +/- 1.4 years; body mass index (BMI) 22 +/- 0.4 kg/m2] and 6 healthy nonobese volunteers (4 males, 2 females; mean age +/- SEM, 35 +/- 3.5 years) underwent two experimental trials at no less than 7-day intervals: GHRH (100 micrograms, i.v.)-induced GH secretion was evaluated after 30 min i.v. infusion of saline (100 ml) or arginine (30 g) in 100 ml of saline. Hyperthyroid patients showed blunted GH peaks after GHRH (13.2 +/- 2.9 micrograms/l) as compared with normal subjects (23.8 +/- 3.9 micrograms/l, p < 0.05). GH peaks after GHRH were only slightly enhanced by arginine in hyperthyroid subjects (17.6 +/- 2.9 micrograms/l), whereas, in normal subjects, the enhancement was clear cut (36.6 +/- 4.4 micrograms/l; p < 0.05). GH values after arginine + GHRH were still lower in hyperthyroid patients with respect to normal subjects. Our data demonstrate that arginine enhances but does not normalize the GH response to GHRH in patients with hyperthyroidism when compared with normal subjects. We hypothesize that hyperthyroxinemia may decrease GH secretion, both increasing somatostatin tone and acting directly at the pituitary level.     

The effect of cyproheptadine on plasma growth hormone (GH) and on somatostatin response to GH-releasing hormone in man

Cyproheptadine (CPH)--a putative serotonin antagonist--is known to inhibit growth hormone (GH) response to various pharmacological stimuli, as well as during sleep. To elucidate the possible site at which this drug takes effect, we examined plasma GH and somatostatin response to i.v. GHRH1-44 (1 microgram/kg body wt.) before and after CPH treatment in 10 healthy volunteers. The oral administration of CPH (8-12 mg daily for 5 days; total dose 56 mg) significantly curbed GH response to GHRH as expressed in peak plasma GH values (32.0 +/- 6.1 micrograms/l vs. 12.6 +/- 3.2 micrograms/l; P less than 0.01) and in integrated GH response area (2368 +/- 517 micrograms x l-1 x 2 h vs. 744 +/- 172 micrograms x l-1 x 2 h; P less than 0.01). Plasma somatostatin levels did not change in response to GHRH.     

Insulinhypoglycemia but not arginine infusion stimulates circulating plasma growth hormone-releasing hormone (GHRH) concentrations in children

The effect of insulinhypoglycemia and arginine infusion on circulating concentrations of plasma growth hormone-releasing hormone (GHRH) and growth hormone (GH) has been studied in 24 children (4.4 to 14.3 years). Plasma GH and GHRH concentrations were determined by RIA. Basal plasma GHRH levels were detectable in the plasma of all patients ranging from 6.8 to 27.1 pg/ml. Injection of 0.1 U/kg body wt. insulin i.v. resulted in an increase of plasma GHRH levels (11.1 +/- 1.4 pg/ml vs. 18.8 +/- 2.6 pg/ml; P less than 0.01) preceding that of plasma GH (1.5 +/- 0.4 ng/ml vs. 13.6 +/- 1.3 ng/ml; P less than 0.01). Infusion of 0.5 gm/kg body wt. arginine hydrochloride did increase GH concentrations (2.0 +/- 0.6 ng/ml vs. 13.9 +/- 2.3 ng/ml; P less than 0.01) but did not change circulating plasma GHRH levels. Since the source of peripheral GHRH concentrations is not known the importance of these findings remains to be determined.     

Effects of gender on exercise-induced growth hormone release.

We examined gender differences in growth hormone (GH) secretion during rest and exercise. Eighteen subjects (9 women and 9 men) were tested on two occasions each [resting condition (R) and exercise condition (Ex)]. Blood was sampled at 10-min intervals from 0600 to 1200 and was assayed for GH by chemiluminescence. At R, women had a 3.69-fold greater mean calculated mass of GH secreted per burst compared with men (5.4 +/- 1.0 vs. 1.7 +/- 0.4 microg/l, respectively) and higher basal (interpulse) GH secretion rates, which resulted in greater GH production rates and serum GH area under the curve (AUC; 1,107 +/- 194 vs. 595 +/- 146 microg x l(-1) x min, women vs. men; P = 0.04). Compared with R, Ex resulted in greater mean mass of GH secreted per burst, greater mean GH secretory burst amplitude, and greater GH AUC (1,196 +/- 211 vs. 506 +/- 90 microg x l(-1) x min, Ex vs. R, respectively; P < 0.001). During Ex, women attained maximal serum GH concentrations significantly earlier than men (24 vs. 32 min after initiation of Ex, respectively; P = 0.004). Despite this temporal disparity, both genders had similar maximal serum GH concentrations. The change in AUC (adjusted for unequal baselines) was similar for men and women (593 +/- 201 vs. 811 +/- 268 microg x l(-1) x min), but there were significant gender-by-condition interactive effects on GH secretory burst mass, pulsatile GH production rate, and maximal serum GH concentration. We conclude that, although women exhibit greater absolute GH secretion rates than men both at rest and during exercise, exercise evokes a similar incremental GH response in men and women. Thus the magnitude of the incremental secretory GH response is not gender dependent.     

The influence of insulin on circulating ghrelin

Ghrelin is a novel peptide that acts on the growth hormone (GH) secretagogue receptor in the pituitary and hypothalamus. It may function as a third physiological regulator of GH secretion, along with GH-releasing hormone and somatostatin. In addition to the action of ghrelin on the GH axis, it appears to have a role in the determination of energy homeostasis. Although feeding suppresses ghrelin production and fasting stimulates ghrelin release, the underlying mechanisms controlling this process remain unclear. The purpose of this study was to test the hypotheses, by use of a stepped hyperinsulinemic eu- hypo- hyperglycemic glucose clamp, that either hyperinsulinemia or hypoglycemia may influence ghrelin production. Having been stable in the period before the clamp, ghrelin levels rapidly fell in response to insulin infusion during euglycemia (baseline ghrelin 207 +/- 12 vs. 169 +/- 10 fmol/ml at t = 30 min, P < 0.001). Ghrelin remained suppressed during subsequent periods of hypoglycemia (mean glucose 53 +/- 2 mg/dl) and hyperglycemia (mean glucose 163 +/- 6 mg/dl). Despite suppression of ghrelin, GH showed a significant rise during hypoglycemia (baseline 4.1 +/- 1.3 vs. 28.2 +/- 3.9 microg/l at t = 120 min, P < 0.001). Our data suggest that insulin may suppress circulating ghrelin independently of glucose, although glucose may have an additional effect. We conclude that the GH response seen during hypoglycemia is not regulated by circulating ghrelin.     

Age-related differences in growth hormone (GH) regulation during strenuous exercise.

This study was designed to investigate the central neuroendocrine mechanisms by which exercise (EX) stimulates growth hormone (GH) release as a function of age. Twelve male subjects, six in their early-to-mid twenties and six in their late sixties or seventies, received a strong GH stimulus either as incremental EX until volitional exhaustion or by administration of GHRH alone or Hex alone two hours after a presumed maximal GH response to combined administration of GHRH plus hexarelin (Hex). Total GH availability was calculated as area under the curve (AUC) over time periods 0 - 120 and 120 - 240 min. The mean AUC in micro g/l x 120 min to GHRH+Hex in the younger group was approximately twice that in the older group (11,260, range 3,947 - 19,007 vs. 5,366, range 2,262 - 8,654). In younger males, the mean AUC to EX (509, range 0 - 1,151) was larger than to GHRH (119, range 0 - 543), but less than that to Hex (919, range 0 - 1,892). In the older group, GH responses to EX and GHRH were abolished (mean AUC: 112, range 0 - 285, and 156, range 30 - 493), respectively) in contrast to the response to Hex (1,077, range 189 - 1,780). These data indicate that maximal GH stimulation by GHRH+Hex results in greater desensitization of GHRH compared to Hex, irrespective of age. We postulate that the abolished responsiveness of GH to EX in older group is due to insufficient disinhibition of hypothalamic somatostatin activity and desensitization of GHRH, while the preserved activity of a central Hex-related pathway is not involved. The GH response to EX in younger males is due to complete inhibition of somatostatin activity and stimulation of a central Hex-related pathway in spite of GHRH desensitization. We conclude that a central Hex-related pathway is the primary factor for EX-induced GH release only in younger males.     

Regulation of leptin mRNA and protein expression in pituitary somatotropes.

Leptin, the ob protein, regulates food intake and satiety and can be found in the anterior pituitary. Leptin antigens and mRNA were studied in the anterior pituitary (AP) cells of male and female rats to learn more about its regulation. Leptin antigens were found in over 40% of cells in diestrous or proestrous female rats and in male rats. Lower percentages of AP cells were seen in the estrous population (21 +/- 7%). During peak expression of antigens, co-expression of leptin and growth hormone (GH) was found in 27 +/- 4% of AP cells. Affinity cytochemistry studies detected 24 +/- 3% of AP cells with leptin proteins and growth hormone releasing hormone (GHRH) receptors. These data suggested that somatotropes were a significant source of leptin. To test regulatory factors, estrous and diestrous AP populations were treated with estrogen (100 pM) and/or GHRH (2 nM) to learn if either would increase leptin expression in GH cells. To rule out the possibility that the immunoreactive leptin was bound to receptors in somatotropes, leptin mRNA was also detected by non-radioactive in situ hybridization in this group of cells. In estrous female rats, 39 +/- 0.9% of AP cells expressed leptin mRNA, indicating that the potential for leptin production was greater than predicted from the immunolabeling. Estrogen and GHRH together (but not alone) increased percentages of cells with leptin protein (41 +/- 9%) or mRNA (57 +/- 5%). Estrogen and GHRH also increased the percentages of AP cells that co-express leptin mRNA and GH antigens from 20 +/- 2% of AP cells to 37 +/- 5%. Although the significance of leptin in GH cells is not understood, it is clearly increased after stimulation with GHRH and estrogen. Because GH cells also have leptin receptors, this AP leptin may be an autocrine or paracrine regulator of pituitary cell function.     

A placebo-controlled trial of intranasal growth hormone-releasing hormone [GHRH(1-44)-NH2] administration in normal young adults

Growth hormone-releasing hormone, GHRH(1-44), was administered intranasally to 16 healthy young adult male volunteers in a placebo-controlled study using a dose of 1,000 micrograms dissolved in two different solvent vehicles: water alone and water with the surface tension-lowering agent Tween 80 (0.12%). The growth hormone (GH)-releasing effects of intranasal GHRH as well as that of the vehicle were established and compared to the effects of 80 micrograms intravenous GHRH. Plasma GH response was assessed by frequent blood sampling over an 180-min period, using both peak response and area under the curve (AUC). The results show that the GH-release effects of intranasal GHRH are comparable whichever vehicle is used, and are similar, with the dose of 1,000 micrograms, to the response obtained following the administration of 80 micrograms intravenous GHRH. Peak GH responses to GHRH (means +/- SEM) were 25.6 +/- 4.2 ng/ml (1,000 micrograms GHRH with water), 32.9 +/- 9.1 ng/ml (1,000 micrograms with water plus Tween 80) and 36.3 +/- 7.8 ng/ml (80 micrograms i.v. administration) (not significant). There was no significant GH response to placebo. Mean peak GH responses occurred after approximately 30 min in all three active treatments (29.2 +/- 2.7, 33.9 +/- 3.2 and 30.9 +/- 3.9 min, respectively). The AUC values (ng.min.ml-1) were not statistically different: 1,914.4 +/- 386.7 (water), 2,176.2 +/- 599.9 (water plus Tween 80) and 2,419.2 +/- 506.9 (i.v.) (not significant). Intranasal GHRH administration was well tolerated in all subjects. Occasional local reactions consisted of a prickly sensation in the nostrils or sneezing irrespective of the vehicle used.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth hormone response to a bolus injection of 1-44 growth-hormone-releasing hormone in very short children with intrauterine onset of growth failure

The release of growth hormone (GH) during the 120 min following a bolus venous injection of 1-44 GH-releasing hormone (GHRH) 2 micrograms/kg was studied in 52 prepubertal children aged 8.4 +/- 2.1 years, having a nonfamilial growth deficiency of prenatal onset (-3.26 +/- 1.13 SDS at birth, -3.22 +/- 0.88 SDS at the time of study) and a normal response to conventional GH stimulation tests. GH release reached a peak level of 96.1 +/- 60.2 microU/ml, being significantly higher than that found in 68 non-GH-deficient very short children whose growth failure had a postnatal onset, and not significantly correlated with the response to conventional tests. 26 of the 52 intrauterine growth retardation (IUGR) patients were re-tested with GHRH in similar conditions after 6-12 months of daily subcutaneous injections of GH and 2 days without. They reached at the second test a peak plasma GH level of 91.7 +/- 56.1 microU/ml, not different from their response to the first test. These data could be taken into consideration for long-term studies of the clinical effects of GH in IUGR children with persisting severe growth deficiency.     

Recruiting of somatotroph cells after combined somatostatin, GHRH and growth hormone (GH) secretagogue stimulation in a study of pituitary GH reserve in prepuberal female rats

Diagnostic confirmation of growth hormone (GH) deficiency in children and adults is based on stimulation tests designed to assess the pituitary reserve by measuring the amount of GH released into the bloodstream; however, the results obtained by this means cannot provide any direct indication of the amount of GH actually produced by pituitary somatotroph cells. The present paper sought to test the hypothesis that release of GH following administration of specific stimuli does not accurately reflect the somatotroph cell response, and that the amount of GH released into the bloodstream may often be greater or smaller than the amount synthesized. GH release and changes in the proportion of somatotroph cells were charted in prepuberal female Wistar rats, following administration of several different GH stimuli: GHRH (1 microg/kg), GHRP-6 (1 microg/kg), GHRELIN (1 microg/kg) and combined GHRH-based treatments, with or without SRIH pretreatment (1 microg/kg) 90 minutes earlier. Peak serum GH values were recorded 15 minutes after administration of GHRH+GHRELIN and GHRH+GHRP-6; maximum stimulation in terms of an increased proportion of somatotroph cells occurred 15 minutes after combined adminstration of GHRH + GHRELIN. SRIH pretreatment (- 90 min) inhibited GH release, with a subsequent "escape" and lack of response to stimulation which lasted at least 30 minutes except following administration of GHRH. However, combined administration of GHRH+GHRELIN maintained stimulation of the somatotroph cell population. In conclusion, the results suggest that the enhanced GH release prompted by stimulation tests used to diagnose GH deficiency in prepuberal female rats does not fully reflect somatroph cell dynamics, and that not all the GH produced and stored by somatotroph cells is released into the bloodstream.     

Effects of acute intravenous injection of two growth hormone-releasing hormones (GHRH 1-40 and 1-29) on serum growth hormone and other pituitary hormones in short children with pulsatile growth hormone secretion

We administered two different growth hormone-releasing hormones (GHRH) to 20 short, prepubertal children who had spontaneous secretion of growth hormone (GH), assessed from 24-hour GH secretion profiles (72 sampling periods of 20 min). We compared one i.v. injection of 1 microgram/kg of GHRH 1-40 with that of GHRH 1-29 regarding serum concentrations of GH, prolactin, luteinizing hormone, follicle-stimulating hormone and IGF-I. The children were allocated to two groups without statistical randomization. Both groups were given both peptides, with at least 1 week in between. The first group started with GHRH 1-40, the other with GHRH 1-29. The peptides both induced an increased serum concentration of GH of the same magnitude: mean maximal peak of 89 +/- 12 mU/l after GHRH 1-40 and 94 +/- 10 mU/l after GHRH 1-29 (n.s.). The mean difference in maximum serum GH concentration in each child after injection was 52 +/- 9 mU/l, range 1-153 mU/l. GHRH 1-29 also induced a short-term, small increase in the concentrations of prolactin (p less than 0.05), luteinizing hormone (p less than 0.01) and follicle-stimulating hormone (p less than 0.05). We conclude that the shorter sequence GHRH 1-29, when given in a dose of 1 microgram/kg, gives a rise in serum concentration of GH similar to that after the native form GHRH 1-40.     

Effect of corticoid therapy on growth hormone secretion

Exogenous corticoids are known to be potent inhibitors of linear growth in children. We investigated the mechanisms underlying growth failure by evaluating growth hormone (GH) release during short-term high-dose prednisone treatment (40 mg/m2/day given orally in 3 divided doses) and 7 days after steroid withdrawal in 7 prepubertal children (4 males, 3 females, age range 3-12 years), affected by acute lymphoblastic leukemia. Patients also received weekly administrations of vincristine (1.5 mg/m2 i.v.), daunomycin (20 mg/m2 i.v.) and L-asparaginase (6,000 IU/m2 i.m.). Corticoid therapy suppressed GH secretion during deep sleep as well as in response to arginine, insulin and GH-releasing hormone (GHRH) administration. A significant recovery of GH responsiveness after drug discontinuation was observed during deep sleep (14.03 +/- 3.47 vs. 1.49 +/- 0.43 ng/ml, p less than 0.025) as well as in response to arginine (13.63 +/- 2.73 vs. 4.95 +/- 1.54 ng/ml, p less than 0.025) and GHRH (32.62 +/- 4.59 vs. 7.27 +/- 3.52 ng/ml, p less than 0.005) but not to insulin (7.12 +/- 0.88 vs. 4.47 +/- 0.96 ng/ml, p = NS). Insulin-like growth factor 1 levels during deep sleep (0.61 +/- 0.13 IU/ml/min) were found to be low in the course of steroid therapy and did not increase after drug withdrawal (0.41 +/- 0.07 IU/ml/min). Our preliminary data suggest that recovery of adrenergic response to insulin does not immediately follow corticosteroid discontinuation.