Oral activity of the growth hormone releasing peptide His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 in rats, dogs and monkeys

The purpose of this study was to evaluate the growth hormone (GH) releasing activity of orally administered His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 (GHRP-6, SK&F 110679) in rats, dogs and monkeys. Rats were administered GHRP-6 orally by gavage or parenterally through femoral artery catheters. Blood was collected before and after GHRP-6 administration for estimation of plasma GH and comparison of GH changes resulting from enteral and parenteral administration of the peptide. GHRP-6 was administered to dogs intravenously (i.v.) through cephalic vein catheters, intragastrically (i.g.) through esophagostomy tubes or intraduodenally (i.d.) through vascular access ports, and blood was collected before and after peptide administration for estimation of plasma GH. Cynomolgus monkeys were administered GHRP-6 i.g., and blood was collected from abdominal aorta for estimation of changes in plasma GH. Enteral activity of GHRP-6 was observed in all 3 species tested. In rats, ED50's for enteral and parenteral administration of GHRP-6 were 4 mg/kg and 28 micrograms/kg, respectively. Thus in rats, enterally administered GHRP-6 was 0.7% as bioactive as the parenterally administered peptide. In dogs GHRP-6 was slightly less potent than in rats, with ED50's for i.g. and i.v. administration approximately 15 mg/kg and 125 micrograms/kg, respectively. However, enteral potency of GHRP-6 in dogs was 0.8% of parenteral potency, and thus, comparable to that in rats. Additionally, comparison of plasma GH levels following i.g. vs i.d. administration in dogs suggested greater activity by the i.d. route. Monkeys were the species most sensitive to enterally administered GHRP-6, with plasma GH increased in those receiving i.g. doses as low as 0.3 mg/kg and an ED50 of 0.75 mg/kg compared to 4 and 15 mg/kg in rats and dogs, respectively. The results of this study demonstrate that GHRP-6 releases GH when administered directly into the gastrointestinal tract. Although enteral activity is approximately 1% of parenteral activity, GHRP-6 is potent, especially in primates which require relatively low doses to provoke GH release. These data suggest that orally active GHRP-6 may provide a practical therapeutic alternative to parenterally administered peptides such as GHRH, especially if enteral activity is enhanced with appropriate formulation.     

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)     

Robust growth hormone (GH) secretion in aged female rats co-administered GH-releasing hexapeptide (GHRP-6) and GH-releasing hormone (GHRH)

Aging is associated with a blunted growth hormone (GH) secretory response to GH-releasing hormone (GHRH), in vivo. The objective of the present study was to assess the effects of aging on the GH secretory response to GH-releasing hexapeptide (GHRP-6), a synthetic GH secretagogue. GHRP-6 (30 micrograms/kg) was administered alone or in combination with GHRH (2 micrograms/kg) to anesthetized female Fischer 344 rats, 3 or 19 months of age. The peptides were co-administered to determine the effect of aging upon the potentiating effect of GHRP-6 on GHRH activity. The increase in plasma GH as a function of time following administration of GHRP-6 was lower (p less than 0.001) in old rats than in young rats; whereas the increase in plasma GH secretion as a function of time following co-administration of GHRP-6 and GHRH was higher (p less than 0.001) in old rats than in young rats (mean Cmax = 8539 +/- 790.6 micrograms/l vs. 2970 +/- 866 micrograms/l, respectively; p less than 0.01). Since pituitary GH concentrations in old rats were lower than in young rats (257.0 +/- 59.8 micrograms/mg wet wt. vs. 639.7 +/- 149.2 micrograms/mg wet wt., respectively; p less than 0.03), the results suggested that GH functional reserve in old female rats was not linked to pituitary GH concentration. The differential responses of old rats to individually administered and co-administered GHRP-6 are important because they demonstrate that robust and immediate GH secretion can occur in old rats that are appropriately stimulated. The data further suggest that the cellular processes subserving GH secretion are intact in old rats, and that age-related decrements in GH secretion result from inadequate stimulation, rather than to maladaptive changes in the mechanism of GH release.     

Physiological relationships between growth hormone level, glycemia and metabolic control in dogs

This study was undertaken to explore the physiological relationships between fasting glycemia, antecedent glycemic control and fasting growth hormone levels in pancreatectomized dogs. In contrast to other studies, we used continuous intravenous infusions of insulin in an attempt not only to normalize fasting plasma glycemia but also to eliminate the characteristic fluctuations of diabetes usually encountered in the postprandial and postabsorptive periods. For comparison, a similar group of healthy animals served as normal controls. In the healthy dogs, fasting growth hormone (GH) levels were stable and well within normal limits for this species, demonstrating an overall mean +/- SD of 2.50 +/- 0.46 ng/ml. In the pancreatectomized group as a whole, the fasting GH levels were significantly elevated (4.63 +/- 2.42 ng/ml, P less than 0.01) and significantly (P less than 0.001) more variable than in the controls. Multiple regression and analysis of variance confirmed the expected significant positive correlation between fasting GH and fasting plasma glucose levels, but also elucidated a heretofore unknown direct relationship between fasting GH levels and the preceding instability of glycemic control.     

Effect of pentobarbital and urethane on the release of hypothalamic somatostatin and pituitary growth hormone

Hypothalamic somatostatin release was investigated in the rat to elucidate the mechanism of anesthetic action on growth hormone (GH) release from the pituitary. Intraperitoneal injection of sodium pentobarbital (5 mg/100 gm B.W.) significantly elevated serum GH levels and increased hypothalamic somatostatin concentration from basal values of 0.98 +/- 0.01 to 1.21 +/- 0.06 ng/mg wet wt. In contrast, urethane (150 mg/100 gm B.W., IP) administration lowered serum GH levels and hypothalamic somatostatin concentration (0.64 +/- 0.04 ng/mg wet wt.). However, the mean concentration of pancreatic somatostatin showed no change in either case. In rats receiving passive immunization with 0.5 ml rabbit antiserum to somatostatin (SRIF-AS), serum GH levels were significantly increased (67.5 +/- 12.3 ng/ml) and did not differ from those in the group treated with normal rabbit serum (NRS) plus pentobarbital (101.3 +/- 18.5 ng/ml). However, serum GH levels in rats injected with SRIF-AS plus pentobarbital were increased to higher values than in rats given SRIF-AS alone. When urethane was administered to rats after passive immunization with SRIF-AS, urethane-induced suppression of serum GH levels was markedly inhibited (5.5 +/- 2.0 vs. 33.5 +/- 7.5 ng/ml). These results suggest a possibility that the changes in serum GH levels observed with pentobarbital or urethane administration may be induced at least in one part by somatostatin released from the hypothalamus.     

Paradoxical growth hormone response following thyroid-stimulating hormone administration in the polycystic ovary syndrome

Growth hormone (GH) and prolactin (PRL) responses after TRH administration were studied in 31 women presenting with the clinical, biochemical and ultrasonographic characteristics of the polycystic ovarian (PCO) syndrome; their results were compared with those of 20 normally menstruating women investigated during the early follicular phase of the cycle. Based on the GH responses two PCO subgroups were observed: (a) nonresponders (n = 16) who showed delta max GH responses (0.7 +/- 0.27 ng/ml, x +/- SE) similar to those of the normals (0.97 +/- 0.20 ng/ml), and (b) responders (n = 15), 48.4% of the PCO patients who showed a paradoxical increase in GH levels (delta max GH, 18.0 +/- 1.96 ng/ml) following thyrotropin-releasing hormone (TRH) administration significantly higher than those observed either in nonresponder PCO patients or in normals. Furthermore, basal GH levels were found to be significantly higher in the responder PCO subgroup (5.65 +/- 0.75 ng/ml) compared to either nonresponders (1.58 +/- 0.21 ng/ml) or normals (1.8 +/- 0.18 ng/ml). However, no correlation was found between basal GH levels and delta max GH responses observed. Additionally, basal PRL and delta max PRL levels following TRH administration did not differ either between the two PCO subgroups or those observed in normal controls. delta 4A, T and E2 levels were similar between the two PCO subgroups. No correlation was found between the delta max GH responses to delta max PRL or the post-luteinizing hormone-releasing hormone stimulation test delta max luteinizing hormone:follicle-stimulating hormone ratio observed or to steroid levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of acebutolol on plasma catecholamine concentrations in anesthetized dogs with ouabain-induced arrhythmias and its direct actions in vitro on the adrenal medulla

We have performed studies on blood hormone dynamics following intravenous administration of acebutolol, a newly synthesized beta-blocker, and its direct action on the adrenal medulla in vitro. Intravenous injection of acebutolol into anesthetized dogs almost doubled the plasma adrenaline and noradrenaline concentrations within 5 to 15 minutes, while renin activity was reduced to approximately two-thirds of the pre-administration level. When arrhythmia was induced in dogs with ouabain, the plasma adrenaline and noradrenaline levels increased to 220 +/- 109 and 392 +/- 84 pg/ml, respectively, from the basal levels of 44 +/- 24 and 140 +/- 43 pg/ml. The restoration of sinus rhythm following the administration of acebutolol was accompanied by a further increase in the plasma adrenaline and noradrenaline levels to 797 +/- 364 and 1226 +/- 263 pg/ml, respectively. A perifusion experiment indicated that acebutolol directly accelerated catecholamine release from the adrenal medulla in pigs.     

Des-enkephalin-gamma-endorphin: bioavailability in rats following the subcutaneous and intramuscular route of administration

A pharmacokinetic study with [3H]des-enkephalin-gamma-endorphin (3H-DE gamma E) was performed in rats after the intravenous, subcutaneous and intramuscular route of administration. Disappearance of non-metabolized 3H-DE gamma E from blood upon intravenous dosing followed a biphasic decay with half-lives of 0.7 +/- 0.3 (+/- S.D.) min for the initial distribution phase and 6.3 +/- 2.7 min for the terminal elimination phase. The central and peripheral volumes of distribution were strikingly high (0.38 and 0.55 1 X kg-1, respectively). Extensive metabolism occurred already within the first minutes after injection. The blood clearance rate was found to be 0.29 +/- 0.12 1 X min-1 X kg-1, which value points to remarkable extrahepatic elimination of the neuropeptide. As compared to the intravenous route of administration, subcutaneous or intramuscular injection of 3H-DE gamma E resulted in low but longer-lasting peptide levels in blood. These levels reached already peak values at 2 min after both routes of administration and then declined to below the limit of detection at 2-3 h. The absolute bioavailability of DE gamma E after subcutaneous injection amounted to 30.9 +/- 16.3% (range 16.0-46.9%), whereas the bioavailability after intramuscular injection was observed to be 3.5 times lower (8.5 +/- 3.0%; range 4.6-12.0%). These data suggest that subcutaneous dosing of DE gamma E might be more effective in displaying CNS activity than the intramuscular route.     

Serum morphine levels in cats during dorsal horn neuron suppression by spinally administered morphine

The degree of serum uptake of morphine following spinal morphine administration was measured in cats. Total serum morphine levels (free plus conjugated) were determined during suppression of noxiously evoked wide dynamic range neuron activity by spinally administered morphine and compared with total serum morphine levels following i.v. administration of similar doses. The serum levels at 30 minutes after spinal application of morphine (a time at which there was significant suppression of noxiously evoked neuronal activity) were low; after 0.1 and 0.25 mg the levels were 6.5 (n=6) and 12.5 (n=5) ng/ml respectively. In contrast, intravenous administration of the same doses (0.1 and 0.25 mg) produced levels at 30 minutes of 24 and 36 ng/ml respectively, while an intravenous dose commonly used in earlier neurophysiologic studies (2 mg/kg) produced serum levels in excess of 400 ng/ml. These results indicate that although there is systemic uptake following spinal administration of morphine, the serum levels achieved are much lower than those following intravenous administration of a comparable dose, and are insufficient to explain the resultant suppression of wide dynamic range neurons.     

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.     

Nasal delivery of a vasopressin antagonist in dogs

The dosage form (drop or spray) and site of administration (dorsal or ventral surface of the nostril) profoundly affect the distribution and clearance of a gamma-emitting 99mTc-labeled diethylenetriamine pentaacetic acid (99mTc-DTPA) solution in dogs. The slowest nasal clearance was observed for dorsally administered drops. Administration of drops to the ventral surface or sprays to either dorsal or ventral surface results in rapid clearance and little deposition in the turbinates. The octapeptide vasopressin antagonist, SKF 101926, was administered intravenously (0.3, 1.0, 3.0, and 10 micrograms/kg) and then on separate occasions intranasally (10, 25, and 50 micrograms/kg as a drop to the ventral surface) to four conscious, trained, female, water-loaded, vasopressin-infused dogs. SKF 101926 reversed the antidiuretic response to vasopressin after administration by either the intravenous or intranasal route in a dose-dependent fashion. Peak dilution of urine occurred within 50- to 60-min postdosing by both routes. Estimated doses to reduce vasopressin antidiuresis by 50% were 1.4 micrograms/kg intravenously and 23 micrograms/kg intranasally. After recovery to at least 70% of antidiuretic base line, and then administration of a second dose of SKF 101926 (3 micrograms/kg), subsequent dilution of urine osmolality was inversely related to the magnitude of the previously administered dose. It is concluded that the estimated relative effectiveness of intranasally administered SKF 101926 is 3-21%, compared with intravenous administration. Acute tachyphylaxis to repeated dosing was observed. The mechanism of the apparent tachyphylaxic response was not elucidated. No tachyphylaxis to less frequent (weekly) dosing was observed.     

Intranasal administration of His-D-Trp-Ala-Trp-D-Phe-LysNH2 (growth hormone releasing peptide) increased plasma growth hormone and insulin-like growth factor-I levels in normal men

The effects of intranasal and iv administration of His-D-Trp-Ala-Trp-D-Phe-LysNH2 (GHRP) on plasma GH, PRL, LH, FSH, TSH, cortisol, insulin, IGF-I as well as GHRH-like immunoreactivity (LI) levels were examined in 6 healthy male subjects. An iv bolus injection of GHRP(1 micrograms/kg BW) caused a remarkable increase in plasma GH levels with a mean (+/- SE) peak of 54.9 +/- 4.2-micrograms/L. In addition an intranasal administration of GHRP resulted in a significant, dose-related increase in plasma GH with peaks of 39.6 +/- 15.3 micrograms/L at a dose of 30 micrograms/kg BW, 14.1 +/- 5.0 micrograms/L at 15 micrograms/kg BW and 7.5 +/- 5.7 micrograms/L at 5 microgram/kg BW. Plasma PRL and cortisol levels were slightly but significantly increased after iv administration of GHRP, whereas GHRP totally failed to affect plasma TSH, LH, FSH, insulin, blood sugar and GHRH-LI levels. Seven consecutive, intranasal administrations of 15 micrograms/kg BW GHRP every 8h were well tolerated in all subjects examined. During this treatment, GH responsiveness to GHRP was not attenuated by desensitization and plasma IGF-I was increased from 94.5 +/- 5.8 micrograms/L before GHRP to 125.8 +/- 6.0 micrograms/L after repeated GHRP administration. These findings indicate that intranasal administration of GHRP stimulates GH secretion and consequently enhances IGF-I production in normal subjects. If GHRP is demonstrated to be beneficial in the treatment of some patients with GH deficiency, the intranasal route of administration may be more useful than the painful injection because a prolonged period is required for the treatment.     

Anti-inflammatory effect of the ghrelin agonist growth hormone-releasing peptide-2 (GHRP-2) in arthritic rats

Chronic arthritis induces hypermetabolism and cachexia. Ghrelin is a gastrointestinal hormone that has been proposed as a treatment to prevent cachexia. The aim of this work was to examine the effect of administration of the ghrelin agonist growth hormone-releasing peptide-2 (GHRP-2) to arthritic rats. Male Wistar rats were injected with Freund's adjuvant, and 15 days later arthritic and control rats were daily injected with GHRP-2 (100 microg/kg) or with saline for 8 days. Arthritis induced an increase in serum ghrelin (P < 0.01) and a decrease in serum concentrations of leptin (P < 0.01), whereas GHRP-2 administration increased serum concentrations of leptin. GHRP-2 increased food intake in control rats but not in arthritic rats. However, in arthritic rats GHRP-2 administration ameliorated the external symptoms of arthritis, as it decreased the arthritis score (10.4 +/- 0.8 vs. 13.42 +/- 0.47, P < 0.01) and the paw volume. In addition, circulating IL-6 and nitrites/nitrates were increased by arthritis, and GHRP-2 treatment decreased the serum IL-6 levels (P < 0.01). To elucidate whether GHRP-2 is able to modulate IL-6 release directly on immune cells, peritoneal macrophage cultures were incubated with GHRP-2 or ghrelin, the endogenous ligand of the growth hormone (GH) secretagogue receptor. Both GHRP-2 (10(-7) M) and ghrelin (10(-7) M) prevented endotoxin-induced IL-6 and decreased nitrite/nitrate release from peritoneal macrophages in vitro. These data suggest that GHRP-2 administration has an anti-inflammatory effect in arthritic rats that seems to be mediated by ghrelin receptors directly on immune cells.     

Atrial natriuretic factor inhibits the CRH-stimulated secretion of ACTH and cortisol in man.

Corticotrophic secretion of ACTH is stimulated by corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP), and suppressed by glucocorticoids. In vitro and preclinical studies suggest that atrial natriuretic factor (ANF) may be a peptidergic inhibitor of pituitary-adrenocortical activity. The aim of this study was to elucidate a possible role of ANF as a modulator of ACTH release in humans. A bolus injection of 100 micrograms human CRH (hCRH) during a 30 min intravenous infusion of 5 micrograms/min human alpha atrial natriuretic factor (h alpha ANF) was administered at 19:00 to six healthy male volunteers. In comparison to saline, a blunted CRH-stimulated secretion of ACTH (mean maximum plasma level +/- SD 45 min after hCRH: saline 46.2 +/- 14.2 pg/ml, h alpha ANF 34.6 +/- 13.8 pg/ml, p-value = 0.007) and a delayed rise (10 min) in cortisol were detected. The maximum plasma cortisol levels remained nearly unchanged between saline and h alpha ANF administration (mean maximum plasma level +/- SD 60 min after hCRH: saline 182 +/- 26 ng/ml, h alpha ANF 166 +/- 54 ng/ml). No effects of h alpha ANF on basal cortisol levels were observed; in contrast, basal ACTH plasma levels were slightly reduced. Basal blood pressure and heart rate remained unaffected. In the control experiment, infusion of 3 IU AVP in the same experimental paradigm increased basal and stimulated ACTH and cortisol levels significantly in comparison to saline. These observations suggest that intravenously administered haANF inhibits the CRH-stimulated release of ACTH in man.     

Cardiovascular effect of intravenously administered thyrotropin-releasing hormone and its concentration in push-pull perfusion of the fourth ventricle in conscious and pentobarbital-anesthetized rats

Changes in the concentration of thyrotropin-releasing hormone (TRH) in cerebrospinal fluid (CSF) were examined by the push-pull perfusion method after intravenous (i.v.) administration of the peptide in conscious and pentobarbital-anesthetized rats. The concentration of endogenous TRH in the perfusate was not changed during the 160-min perfusion period and was similar to that in the CSF (0.92 +/- 0.26 ng/ml) collected before the perfusion in conscious as well as in anesthetized rats. After i.v. administration of TRH (5 mg/kg) to the conscious rats, the peptide concentration in the perfusate increased to 42.23 +/- 14.33 ng/ml during the first 20 min and gradually returned to the basal level 2 hr after administration. The total amount of TRH detected in the perfusate was 20.0 ng. It was reduced by 75% in the anesthetized animals. The increases in blood pressure and heart rate, seen after i.v. as well as intracerebroventricular administration of TRH in the conscious rats, was significantly inhibited in the anesthetized rats. These results indicate that systemically administered TRH exerts its cardiovascular effect at central site(s), and that the transportation and the effect of the peptide is suppressed by pentobarbital anesthesia.     

Acute exercise has no effect on ghrelin plasma concentrations.

Exercise is a potent, dose-dependent stimulus of growth hormone (GH) secretion. The hypothalamic peptides, GH-releasing hormone (GHRH) and somatostatin are regarded as major regulators of this stimulation. The role of the stomach-derived peptide ghrelin, which has been shown to exert strong GH releasing effects, has not been fully characterized yet. We therefore studied GH and ghrelin plasma concentrations in response to graded levels of exercise in eight healthy young volunteers. After determination of their individual maximal exercise capacity, all individuals underwent a treadmill exercise at 50 %, 70 %, and 90 % of maximum oxygen consumption (VO (2)max) on different days. Maximal GH response to exercise was observed after 40 minutes at 50 % VO (2)max and after 20 minutes at 70 and 90 % VO (2max). GH serum concentrations increased significantly at all three exercise intensities (GH peak concentrations were 5.8 +/- 2.3 ng/ml, 12.0 +/- 3.2 ng/ml, and 9.8 +/- 4.7 ng/ml, respectively). In contrast, ghrelin plasma concentrations remained unchanged at all three workloads. Assuming that the sensitivity of the GH neuroendocrine/metabolic regulation of GH is unaltered, ghrelin does not participate in the regulation of the GH response to exercise in healthy males.     

Intranasal midazolam in piglets: pharmacodynamics (0.2 vs 0.4 mg/kg) and pharmacokinetics (0.4 mg/kg) with bioavailability determination

Intranasal midazolam was studied in two series of piglets: series 1, n = 20 (18 +/- 3 kg), a randomized double blind pharmacodynamic study to compare doses of 0.2 mg/kg and 0.4 mg/kg; series 2, n = 9 (42 +/- 8 kg), a pharmacokinetic study with a 0.4 mg/kg dose administered either intravenously (i.v.) or intranasally (i.n.) in a cross-over protocol with a one-week wash-out period between each. In series 1, midazolam caused significant anxiolysis and sedation within 3 to 4 min, without a significant difference between 0.2 and 0.4 mg/kg doses for any of the studied parameters. In series 2, after intranasal midazolam administration of 0.4 mg/kg, plasma concentrations attained a maximum (Cmax) of 0.13 +/- 0.04 mg/l at 5 min (median Tmax) and remained higher than 0.04 mg/l until 60 min. The bioavailability factor (F) in this study was F = 0.64 +/- 0.17 by the intranasal route. The terminal half-life (T1/2 lambda z) = 145 +/- 138 min was comparable with the i.v. administration half-life (158 +/- 127 min). In conclusion, optimal intranasal midazolam dose in piglets was 0.2 mg/kg, which procures rapid and reliable sedation, adapted to laboratory piglets.     

Neither intravenous nor intracerebroventricular administration of obestatin affects the secretion of GH, PRL, TSH and ACTH in rats

To examine the effect of obestatin, a recently identified peptide derived from preproghrelin, on pituitary hormone secretion, obestatin was administered in anesthetized male rats. Intravenous administration of obestatin did not show any effect on plasma GH, PRL, ACTH and TSH levels. Since obestatin has been reported to have opposite effects of ghrelin in regulating food intake, gastric emptying and intestinal contractility, GH suppressive effect, which is opposite effect of ghrelin, was tested. Intravenous administration of GHRH or GHRP-2, a ghrelin receptor ligand, resulted in a marked plasma GH elevation. However obestatin did not show any effect on GHRH- or GHRP-2-induced GH rise. Furthermore intracerebroventricular administration of obestatin also did not influence plasma GH, PRL, ACTH and TSH levels. These findings suggest that obestatin has no effect on pituitary hormone secretions despite the presence of GPR39, a receptor for obestatin, in the pituitary.     

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.     

Induction of growth hormone release by dioscin from Dioscorea batatas DECNE

In this study, dioscin was isolated from Dioscoreae Rhizoma (DR), which is the rhizome of Dioscorea batatas D(ECNE). that inhabits broad areas of Korea and Japan. To determine whether dioscin induced growth hormone (GH) release, we evaluated its induction effects on GH release both in vitro and in vivo. The 70% methanol extract of DR, and its n-hexane and n-BuOH fractions, induced rat GH (rGH) release in rat pituitary cells 10-fold, 8-fold, and 5- fold higher than the control (0.36 +/- 0.02 nM), respectively (p < 0.05 each). The dioscin-induced rGH release of the cells was concentration-dependent and its ED(50) was 1.14 x 10(-5) M. Within 90 minutes after intravenous administration of 10 microg/kg (p < 0.05 at t(max)), dioscin caused the greatest increase in rGH concentration (C(max)) in the rat plasma (34.16 +/- 14.10 ng/ml) (n = 4), which was twice as high as the control group (12.88 +/- 3.29 ng/ml) (n = 27).