Effect of dopamine on plasma growth hormone and prolactin levels in normal and acromegalic subjects.

In contrast with other dopaminergic drugs (L-dopa, apomorphine or bromocriptine) a 280 mug/min dose of dopamine infused for 120 min failed to induce an increase in plasma GH in 9 normal subjects. During dopamine infusion, no significant change in the GH response to arginine was also noted, whereas prolactin displayed a significant fall. In 15 acromegalic patients, on the other hand, the drug caused a marked fall in both GH (mean+/-SE; 71.1%+/-5.6) and prolactin (mean+/-SE; 67.6%+/-4.0) followed by a distinct rebound after the end of the test. There was a very close relation (P less than 0.001) between the maximum per cent decrease in GH during dopamine and after 2.5 mg bromocriptine by mouth. Dopamine also inhibited the GH response to TRH (4 patients). Since dopamine does not readily cross the blood-brain barrier, these results suggest that the stimulating effect of dopaminergic drugs on GH secretion in the normal subject is exerted via the CNS, whereas in acromegaly there is a direct action on structures lying outside the blood-brain barrier, probably in the hypophysis. Dopaminergic inhibition of prolactin is primarily the result of action on the hypophysis, as well as on the hypothalamus, in both normal and acromegalic subjects.

Changes in plasma growth hormone levels in normal and acromegalic subjects following administration of 2-bromo-alpha-ergocryptine.

2-Bromo-alpha-ergocryptine (CB-154), AN ERGOT ALKALOID THAT STIMulates dopaminergic receptors, caused a widely varying, but significant increase in plasma GH levels in normal subject whereas a marked and protractedfall in values was observed in some patients with acromegaly. It is suggested that these effects were mediated by activation of either hypothalamic or hypophyseal dopaminergic receptors. The fact that GH values fell to or near normal levels in 4/8 cases suggests that CB-154 may have therapeutic possibilities in acromegaly.

Chronic treatment with pirenzepine decreases growth hormone secretion in insulin-dependent diabetes mellitus.

We and others previously reported that nocturnal GH secretion in patients with insulin-dependent diabetes mellitus is blunted by acute cholinergic muscarinic blockade with pirenzepine. In this study, we investigated whether this inhibitory effect on GH secretion persists during chronic pirenzepine administration, and if pirenzepine administration affects glycemic control. Nocturnal GH secretion was studied from 2300-0800 h before and after one month of pirenzepine administration (100 mg/day, orally, given at 2300 h) in 13 diabetic patients receiving their usual insulin treatment. GH secretion (GH area under curve) was blunted after pirenzepine administration [mean, 877 +/- 215 (+/- SE) vs. 1407 +/- 311 micrograms/L.min; P less than 0.002]. During pirenzepine administration, hemoglobin A1c significantly decreased (P less than 0.02), and 4 of the 13 patients had lower daily insulin requirements (5-23 U/day), but there was no significant change for the group as a whole. These results indicate that the inhibitory effect of pirenzepine on GH secretion persists when pirenzepine is given chronically and that pirenzepine seems to improve the metabolic control of the patients.

Effectiveness and tolerability of long term treatment with cabergoline, a new long-lasting ergoline derivative, in hyperprolactinemic patients.

Cabergoline (CAB) is a new oral dopaminergic compound showing a very long-lasting PRL-lowering activity and reported to be well tolerated. The efficacy and tolerability of chronic treatment with CAB in 30 female hyperprolactinemic patients, aged 18-52 yr (6 microadenomas, 3 macroadenomas, and 21 functional hyperprolactinemias), were studied. In a group of 10 patients who received CAB (0.8 mg once weekly or 0.4 mg twice weekly) for 8 weeks PRL levels normalized while on treatment and remained normal (8 patients) or greatly reduced (1 patient) for 1-2 months after discontinuation of the drug. Twenty-six patients underwent chronic treatment (6-12 months) with an initial dose of 0.5 mg once weekly, subsequently increased to 1-2 mg in 10 patients and decreased in the other 2. Due to severe side-effects CAB was discontinued in 3 patients, in 1, 8, and 12 weeks. A significant reduction of PRL levels was already observed after the first week of treatment (mean +/- SEM basal values, 90.1 +/- 13.3 vs. 29.5 +/- 6.3 micrograms/L; P less than 0.001). Twenty-two patients had normal PRL levels in 1-36 weeks (mean, 6 weeks) with 0.5-2 mg CAB. Twenty-two patients resumed regular menses; 2 patients became pregnant after 3-11 months of treatment. Thirteen patients complained of side-effects (nausea, hypotension, headache, gastric pain, dizziness, and weakness) that disappeared with time in 10 of them. The comparison with a previous bromocriptine treatment regimen in 20 patients had shown that the number of patients requiring discontinuation of the latter drug was significantly higher (7 vs. 3 patients; P less than 0.001). However, 2 patients who needed to discontinue CAB were able to tolerate bromocriptine therapy. A computed tomographic scan performed after 12 months of therapy in 7 patients showed a significant reduction (50%) of the adenoma in 5. In conclusion, our results show that CAB is a well tolerated new dopamine agonist with long-lasting activity that represents an advance in chronic medical treatment of hyperprolactinemic conditions.

Blockade of hp-GRF-40-induced GH release in normal men by a cholinergic muscarinic antagonist.

In five healthy young men, pretreatment with the cholinergic muscarinic antagonist pirenzepine (0.6 mg/kg iv) almost completely abolished the rise in plasma growth hormone (GH) elicited by an iv bolus injection of 1 microgram/kg human pancreatic GH-releasing factor 1-40 (hp-GRF-40). These data demonstrate that cholinergic receptor sites involved in GH-releasing mechanisms do not interact with GRF-secreting structures in the central nervous system. A mechanism mediated via hypothalamic release of somatostatin or, alternatively, a direct pituitary site of action, can be postulated for the blocking effect of pirenzepine.

Carbidopa inhibits the growth hormone- and prolactin-suppressive effect of L-dopa in acromegalic patients.

The plasma GH, PRL, TSH, and dopamine (DA) responses to an infusion of L-dopa were examined in six acromegalic patients before and after pretreatment with carbidopa, a drug which inhibits the peripheral conversion of L-dopa to DA. Carbidopa neither modified baseline DA nor induced changes in baseline GH, PRL, or TSH levels. The drug instead markedly reduced the L-dopa-induced DA rise, an effect which was concomitant to a striking reduction of the suppressive effect of L-dopa on plasma GH and a partial inhibition of the suppressive effect of L-dopa on plasma PRL. TSH levels did not change either after L-dopa alone or L-dopa plus carbidopa. These data demonstrate that in "responder" acromegalics, L-dopa inhibits GH secretion through its peripheral conversion to DA and not via activation of central DA neurotransmission. For the effect of L-dopa on PRL secretion, in addition to a peripheral dopaminergic component, a central component cannot be disregarded.

Defective regulation of prolactin secretion after successful removal of prolactinomas.

The PRL response to nomifensine (Nom), an indirect DA agonist; domperidone (Dom), a DA receptor antagonist; and TRH, which directly stimulates the PRL-secreting cells, was evaluated 2-53 months after surgery in 13 patients in whom successful removal of a prolactinoma had resulted in normal serum PRL levels and return of regular menses or libido and potency. In addition, the pattern of TSH secretion in response to Dom and the spontaneous rise in plasma PRL of 6 cured patients during pregnancy were evaluated. Nom induced an inconsistent decrease in basal PRL levels, a pattern contrasting with that in healthy women in whom plasma PRL was markedly suppressed after administration of the drug. Dom and TRH elicited a significant rise of basal PRL levels, but the rise was markedly lower than that occurring in the control group. The TSH increment after Dom treatment was lower than that before surgery, though higher than that in the controls. Evaluation of individual patients showed that only one patient had a normal PRL response to either Nom or Dom, while the TSH response to the latter returned to normal in five of seven patients. During pregnancy, plasma PRL rose inconsistently in the patients, and PRL levels were generally lower than those in normal pregnant women. These results suggest the presence of an abnormality in the dopaminergic mechanism(s) of PRL control before and after adenomectomy or, less likely, the existence of impaired pituitary function or reserve.

Growth hormone-releasing activity of hexarelin, a new synthetic hexapeptide, after intravenous, subcutaneous, intranasal, and oral administration in man.

We evaluated the GH-releasing activity of hexarelin, a new synthetic hexapeptide, after i.v. (1 and 2 micrograms/kg), sc (1.5 and 3 micrograms/kg), intranasal (20 micrograms/kg), and oral (po; 20 and 40 mg) administration to 12 healthy young volunteers. Reference treatments were i.v. saline and GH-releasing hormone (GHRH; 1 microgram/kg). GH release (mean +/- SEM) after the i.v. dose of 1 microgram/kg hexarelin [area under the curve (AUC), 3175 +/- 506 micrograms/min.L] was about 2 times higher than that induced by 1 microgram/kg GHRH (AUC, 1544 +/- 161 micrograms/min.L; P < 0.001). Hexarelin (2 micrograms/kg, i.v.) elicited a further increase in GH levels (AUC, 4422 +/- 626 micrograms/min.L) compared to the 1 microgram/kg dose. The GH response to 2 micrograms/kg hexarelin, i.v., was very reproducible (AUC, 4016 +/- 563 vs. 3959 +/- 803 micrograms/min.L). The sc administration of hexarelin produced a dose-dependent GH response (AUC, 3180 +/- 392 and 4459 +/- 566 micrograms.min.L with 1.5 and 3 micrograms/kg, respectively). Intranasal administration of 20 micrograms/kg hexarelin induced GH release (AUC, 2642 +/- 452 micrograms/min.L) similar to that caused by 1 microgram/kg, i.v. Twenty and 40 mg hexarelin, po, produced a dose-related increase in GH levels (AUC, 2278 +/- 442 and 4079 +/- 514 micrograms/min.L). Biological bioavailabilities were 77.0 +/- 10.5%, 4.8 +/- 0.9%, and 0.3 +/- 0.1% for the sc, intranasal, and po routes, respectively. This study shows that the GH response to hexarelin administered by the i.v. route has a limited variability and is superior to the response to GHRH. The GH-releasing activity appeared to be dose dependent. Thus, hexarelin could be clinically useful to stimulate GH secretion in humans.

Comparison between insulin-induced hypoglycemia and growth hormone (GH)-releasing hormone + arginine as provocative tests for the diagnosis of GH deficiency in adults.

There is now wide consensus that, within an appropriate clinical context, GH deficiency (GHD) in adults must be shown biochemically by provocative testing of GH secretion and that appropriate cut-off limits have to be defined for each provocative test. Insulin-induced hypoglycemia (ITT) is indicated as the test of choice, and severe GHD, to be treated with recombinant human GH replacement, is defined by a GH peak response to ITT of less than 3 micrograms/L. GHRH + arginine (GHRH + ARG) is one of the most promising tests in alternative to ITT. In fact, it has been reported as a potent, reproducible, and age-independent test and that it is able to distinguish between GHD and normal adults. The aim of the present study was to compare the GH response to ITT and GHRH + ARG in a large group of hypopituitary adults (n = 40; 29 male and 11 female; age: 36.4 +/- 2.1 yr). The third centile limit of the peak GH response to ITT has been reported as 5 micrograms/L, whereas in our lab, that to GHRH + ARG is 16.5 micrograms/L. In hypopituitary adults, the mean peak GH response to ITT (1.5 +/- 0.2 micrograms/L, range: 0.1-8.5 micrograms/L) was lower (P < 0.001) than that to GHRH + ARG (3.0 +/- 0.4 micrograms/L, range 0.1-12.0 micrograms/L), though there was positive correlation (r = 0.61, P < 0.001) between the GH responses to the 2 tests. The peak GH response to GHRH + ARG, but not that to ITT, was positively (though weakly) associated with insulin-like growth factor-I levels (r = 0.35, P < 0.03). Childhood and adult onset GHD patients, as well as patients with single and multiple pituitary insufficiencies, had similar peak GH responses to ITT or GHRH + ARG. Analyzing individual GH responses, 4/40 (10%) of the hypopituitary patients had GH peaks higher than 5 micrograms/L after ITT; moreover, 3 other patients (7%) had GH peaks, after ITT, higher than 3 micrograms/L. On the other hand, after GHRH + ARG, all patients had GH peaks lower than 16.5 micrograms/L, whereas 21/40 (52.5%) had GH peaks higher than 3 micrograms/L. Because 3 micrograms/L is the arbitrary cut-off for ITT, the third centile limit of which is 5 micrograms/L, we arbitrarily considered 9 micrograms/L as the cut-off point for GHRH + ARG. It is noteworthy that 37/40 (92.5%) patients had a GH peak, after GHRH + ARG, below this limit. In conclusion, our present results confirm that the ITT test is a reliable provocative test for the diagnosis of adult GHD, whereas they show that the GHRH + ARG test is, at least, as sensitive as the ITT test (provided that appropriate cut-off limits are considered). Note that even the arbitrary cut-off point below which severe GHD is demonstrated has to be appropriate to the potency of the test.

Adrenocorticotropin- and cortisol-releasing effect of hexarelin, a synthetic growth hormone-releasing peptide, in normal subjects and patients with Cushing's syndrome.

GH-releasing peptides (GHRPs) are synthetic, nonnatural molecules that strongly stimulate GH secretion, but also slightly increase PRL, ACTH, and cortisol levels in man. To investigate the mechanism underlying the ACTH- and cortisol-releasing activity of GHRPs in man, we compared the ACTH- and cortisol-releasing activity of Hexarelin (HEX; 2.0 micrograms/kg, iv), a hexapeptide belonging to the GHRP family, with that of human CRH (hCRH; 2.0 micrograms/kg, iv) in normal subjects (6 men and 6 women, 24-68 yr old) and patients with Cushing's syndrome (2 men and 15 women, 16-68 yr old). The GH response to HEX administration was also studied. In normal subjects, HEX administration significantly increased ACTH (peak us. baseline, mean +/- SD, 32.4 +/- 17.7 vs. 16.3 +/- 7.2 pg/mL; P < 0.005) and cortisol levels (135.9 +/- 51.0 vs. 110.0 +/- 31.6 micrograms/L; P < 0.01). The ACTH and cortisol responses to hCRH [35.7 +/- 13.2 vs. 17.1 +/- 7.7 pg/mL (P < 0.01) and 162.8 +/- 50.1 vs. 102.8 +/- 28.1 micrograms/L (P < 0.01), respectively] were similar to the responses to HEX. The stimulatory effect of HEX, but not that of hCRH, on both ACTH and cortisol secretion in Cushing's disease was clearly higher (P < 0.01) than that observed in normal subjects. In fact, in Cushing's disease both HEX and hCRH elicited a clear increase in ACTH levels [381.1 +/- 350.0 vs. 52.4 +/- 25.0 (P < 0.005) and 100.0 +/- 86.2 vs. 53.3 +/- 29.7 pg/mL (P < 0.01), respectively but the ACTH increase induced by HEX was about 7-fold greater (P < 0.02) than that induced by hCRH. Similarly, both HEX and hCRH elicited a significant increase in cortisol levels [366.9 +/- 189.5 vs. 189.7 +/- 86.3 micrograms/L (P < 0.005) and 209.9 +/- 125.4 vs. 167.2 +/- 96.3 micrograms/L (P < 0.02), respectively], but the cortisol increase induced by HEX was about 4-fold greater (P < 0.05) than that induced by hCRH. In patients with Cushing's syndrome due to adrenal adenoma or ectopic ACTH, no change in ACTH and cortisol levels was observed after either HEX or hCRH administration. The peak GH response to HEX in normal subjects was clearly higher (P < 0.03) than that in hypercortisolemic patients (45.8 +/- 20.5 vs. 22.4 +/- 21.1 micrograms/L). In conclusion, the ACTH- and cortisol-releasing activity of HEX is similar to that of hCRH in normal subjects, whereas it is dramatically enhanced in patients with Cushing's disease. This evidence indicates the importance of the ACTH-releasing activity of GHRPs and suggests that it could be at least partially independent of CRH-mediated mechanisms. As the stimulatory effect of HEX on ACTH and cortisol secretion is lost in patients with Cushing's syndrome due to adrenal adenoma or ectopic ACTH, these findings suggest the usefulness of GHRPs to investigate the activity of the hypothalamo-pituitary-adrenal axis in pathophysiological conditions and possibly to differentiate pituitary from ectopic ACTH-dependent Cushing's syndrome.

Long term therapy of patients with macroprolactinoma using repeatable injectable bromocriptine.

The efficacy and tolerability of a long term treatment (21-53 months; mean, 36) with a new injectable form of bromocriptine (Parlodel LAR, Sandoz) was assessed in 13 patients (9 males and 4 females, aged 14-68 yr) with macroprolactinoma. Parlodel LAR was administered deeply im once monthly, with 50 mg as the first dose. Depending on the patient's tolerability to the drug and the PRL levels, the dose was individually progressively increased to 100 mg (2 patients), 150 mg (3 patients), or 250 mg (4 patients). Persistently normal PRL levels were recorded in 4 patients even after the first injection and in 5 other patients treated with higher doses of Parlodel LAR (2 patients with 100 mg/month; 3 patients with 150 mg/month). The remaining 4 patients who were treated with 250 mg/month had a marked reduction of PRL levels (72-94%), but did not reach normalization. Two patients treated with 150 mg/month maintained normoprolactinemia in spite of subsequent dose reduction of Parlodel LAR to 50-100 mg/month. In 1 patient PRL plasma concentrations remained within normal range for 3 months after the transitory discontinuation of Parlodel LAR at the end of the first year of therapy. Regular menses were resumed in 1 of 3, and galactorrhea disappeared in 2 of 3 women. All male patients had a return of libido and potency; gynecomastia disappeared in both male patients, and galactorrhea disappeared in 1 of 2 male patients. Visual fields improved in all 5 patients; complete normalization occurred in 2 of them. A consistent shrinkage of the macroadenoma (23-100%) at different times after therapy was shown by magnetic resonance imaging and/or computed tomography in 12 of 13 patients. Six patients reported mild/moderate side-effects (nausea, vomiting, orthostatic hypotension, or dizziness) within 24 h after the first injection. In 2 of these patients, mild side-effects persisted for 1-2 days after the first 3-6 injections, and in one patient, mild nausea was reported after each injection. In conclusion, in patients with macroprolactinoma, Parlodel LAR is an effective and well tolerated preparation of bromocriptine when administered once a month.

In obesity the somatotrope response to either growth hormone-releasing hormone or arginine is inhibited by somatostatin or pirenzepine but not by glucose.

It is known that spontaneous and stimulated GH secretion is reduced in obesity. On the other hand, it has been recently reported that, in obese subjects, plasma GH levels did not change during a hyperglycemic clamp. To further study the sensitivity of somatotrope cells to inhibitory influences in obesity, we studied the effect of somatostatin, pirenzepine, or glucose on the GH response to GHRH or arginine in 32 obese patients and 30 controls. Basal GH levels were lower in obese than in normal subjects (1.0 +/- 0.6 vs. 4.8 +/- 0.7 micrograms/L, P < 0.05), while insulin-like growth factor-I levels were similar in both groups (137.3 +/- 13.2 vs. 138.8 +/- 12.2 micrograms/L). In obese as well as in control subjects pirenzepine abolished the GH response to either GHRH (AUC0-120: 43.7 +/- 9.6 vs. 258.3 +/- 59.9 micrograms/L/h, P < 0.04 and 113.0 +/- 75.0 vs. 870.5 +/- 255 micrograms/L.h, P < 0.01, respectively) or arginine (6.5 +/- 2.5 vs. 118.7 +/- 55.9 micrograms/L.h, P < 0.05 and 47.7 +/- 7.3 vs. 334.0 +/- 157.5 micrograms/L.h, P < 0.01, respectively). Differently from pirenzepine, glucose blunted the GH response to either GHRH or arginine in control subjects (260.8 +/- 38.3 vs. 479.5 +/- 83.9 micrograms/L.h, P < 0.03 and 294.8 +/- 46.3 vs. 625.1 +/- 139.1 micrograms/L.h, P < 0.05, respectively), but failed to modify it in obese patients (193.7 +/- 39.4 vs. 172.4 +/- 33.6 micrograms/L.h and 121.1 +/- 43.4 vs. 155.1 +/- 39.7 micrograms/L.h, respectively). On the other hand, somatostatin deeply blunted the GHRH-induced GH release in obese patients (58.5 +/- 25.4 vs. 548.7 +/- 196.6 micrograms/L.h, P < 0.05) as well as in controls (181.4 +/- 44.4 vs. 759.7 +/- 46.6 micrograms/L.h, P < 0.04). In conclusion, our results show that, in obesity, the stimulated GH release is refractory to the inhibitory effect of glucose but not of pirenzepine, in spite of their likely common mechanism of action, i.e. increase of hypothalamic somatostatin release. Exogenous somatostatin is able to abolish GH secretion both in normal and obese subjects. These data suggest the existence of a peculiar inhability of hyperglycemia to trigger somatostatinergic release in obesity.

Growth hormone (GH) responsiveness to combined administration of arginine and GH-releasing hormone does not vary with age in man.

At present, the mechanism(s) underlying the reduced spontaneous and stimulated GH secretion in aging is still unclear. To obtain new information on this mechanism(s), the GH responses to both single and combined administration of GH-releasing hormone (GHRH; 1 microgram/kg iv) and arginine (ARG; 30 g infused over 30 min), a well known GH secretagogue probably acting via inhibition of hypothalamic somatostatin release, were studied in seven elderly normal subjects and seven young healthy subjects. Basal GH levels were similar in both groups, while insulin-like growth factor-I levels were lower in elderly subjects (76.7 +/- 9.2 vs. 258.3 +/- 29.2 micrograms/L; P = 0.01). In aged subjects GHRH induced a GH increase (area under the curve, 314.9 +/- 91.9 micrograms/L.h) which was lower (P = 0.01) than that in young subjects (709.1 +/- 114.4 micrograms/L.h). On the other hand, the ARG-induced GH increase in the elderly was not significantly different from that in young subjects (372.8 +/- 81.8 vs. 470.6 +/- 126.5 micrograms/L.h). ARG potentiated GH responsiveness to GHRH in both elderly (1787.1 +/- 226.0 micrograms/L.h; P = 0.0001 vs. GHRH alone) and young subjects (2113.0 +/- 444.3 micrograms/L.h; P = 0.001 vs. GHRH alone). The potentiating effect of ARG on the GHRH-induced GH response was greater in elderly than in young subjects (1013.0 +/- 553.5% vs. 237.9 +/- 79.1%; P = 0.0001); thus, the GH increase induced by combined administration of ARG and GHRH overlapped in two groups. In conclusion, these results show that, differently from the GHRH-induced GH increase, the somatotroph response to combined administration of ARG and GHRH does not vary with age. Our finding suggests that an increased somatostatinergic activity may underlie the reduced GH secretion in normal aging.

Growth hormone-releasing activity of hexarelin, a new synthetic hexapeptide, before and during puberty.

The objective of this study was to verify the GH-releasing activity of a synthetic hexapeptide, hexarelin (HEX), before and during puberty. Ninety-six children (54 boys and 42 girls, aged 4.1-17.4 yr) were studied. Fifty-two of the children were prepubertal, and the other 44 were in pubertal stage II-IV. The GH response to 2 micrograms/kg HEX, iv (n = 56), was higher (P < 0.001) than that induced by 1 microgram/kg GHRH, iv (n = 33). The iv dose of 2.0 micrograms/kg HEX induced a greater GH increase (P < 0.02) than the 1.0 microgram/kg dose. The GH-releasing effect of 10 mg HEX, orally, was greater (P < 0.03) than that of 1.0 microgram/kg GHRH, iv (n = 7). The iv dose of 2 micrograms/kg HEX elicited an increase in GH levels that was higher in pubertal children than in prepubertal children (77.5 +/- 8.5 vs. 39.4 +/- 4.4 micrograms/L; P < 0.001). Before puberty, there was no sex-dependent difference in the GH response to HEX. It increased during puberty (P < 0.05 and P < 0.002 for boys and girls, respectively), when it was higher (P < 0.05) in girls than in boys. In contrast, GH responses to GHRH were not related to sex differences and/or puberty. In conclusion, HEX is a potent and reproducible stimulus of GH secretion in children. The effect of HEX increases in puberty, with girls showing a more marked GH response.

Acute clonidine administration potentiates spontaneous diurnal, but not nocturnal, growth hormone secretion in normal short children.

It has been shown that alpha 2-adrenoreceptor activation induced by clonidine (CLON) increases plasma GH levels in both adults and children. In this study the effects of CLON (150 micrograms/m2, orally) on GH secretion were studied both in the morning (from 0800-1100 h) and at night (from 2300-0200 h) in nine short children previously shown to have normal spontaneous nocturnal GH secretion. In the morning, CLON induced a GH increase higher than placebo [peak (mean +/- SEM), 23.8 +/- 4.3 vs. 3.4 +/- 1.4 micrograms/L; P = 0.0001; area under curve (AUC), 624.4 +/- 62.7 vs. 135.6 +/- 33.3 micrograms/L.h; P less than 0.00001]. In the night, no difference was observed between GH secretion after CLON (peak, 15.4 +/- 3.2 micrograms/L; AUC, 562.2 +/- 57.5 micrograms/L.h) and placebo (peak, 13.1 +/- 4.7 micrograms/L; AUC, 497.2 +/- 83.5 micrograms/L.h). Spontaneous GH secretion was higher during the night than in the morning (P = 0.0001), whereas nocturnal GH secretion overlapped with that in the morning after CLON. The data presented show that alpha 2-adrenoreceptor activation is probably mediated by increased endogenous GHRH release; our results suggest that the endogenous GHRH secretion is maximally stimulated at night.

Enhancement of cholinergic tone by pyridostigmine promotes both basal and growth hormone (GH)-releasing hormone-induced GH secretion in children of short stature.

Increased cholinergic tone induced by pyridostigmine (PD) increases basal plasma GH levels and potentiates the GH response to GHRH in normal adults. In this study the effects of PD (60 mg, orally) on both basal and GHRH (1 microgram/kg)-induced GH secretion in seven children with familial short stature (FSS), six with GH deficiency (GHD) and 10 with constitutional growth delay (CGD) were studied and compared with results obtained by stimulation with insulin-induced hypoglycemia (IH) and GHRH alone. The mean peak plasma GH levels were variable, but individual values were frequently low in all groups after both IH [FSS, 9.7 +/- 1.3 (+/- SEM) ng/mL; GHD, 1.6 +/- 0.4 ng/mL; CGD, 7.0 +/- 0.8 ng/mL] and GHRH (FSS, 23.8 +/- 6.6 ng/mL; GHD, 11.1 +/- 5.8 ng/mL; CGD, 15.1 +/- 4.5 ng/mL) administration. PD induced GH responses (FSS, 14.5 +/- 1.6 ng/mL; GHD, 3.8 +/- 0.8 ng/mL; CGD, 18.3 +/- 3.2 ng/mL) that in many children in the FSS and CGD groups were higher than those after IH and GHRH treatment. PD clearly increased the GH response to GHRH in all children [FSS, 69.5 +/- 9.4 ng/mL (P less than 0.01 vs. other stimuli); GHD, 18.0 +/- 7.5 ng/mL; CGD, 50.0 +/- 8.5 ng/mL (P less than 0.01 vs. other stimuli)]. We conclude that in children with short stature, as in adults, enhancement of cholinergic tone increases both basal and GHRH-induced GH secretion, and that PD plus GHRH is the best provocative stimulus for evaluating the somatotroph response.

Intranasal administration of neostigmine potentiates both intravenous and intranasal growth hormone (GH)-releasing hormone-induced GH release in short children.

Administration of cholinergic agonists increases both basal and GH-releasing hormone (GHRH)-induced GH secretion, probably acting via inhibition of endogenous somatostatin release. The aim of our study was to verify in two groups of children with idiopathic short stature the effect of intranasal administration of neostigmine (inNS; 3 mg), a cholinesterase inhibitor, on basal GH levels as well as on the somatotroph response to GHRH when the peptide was administered either iv (ivGHRH; 1 microgram/kg) or intranasally (inGHRH; 10 micrograms/kg). In group A (n = 6; age, 10.6-16.0 yr) inNS induced a significant GH increase [inNS vs. saline, area under the curve (AUC; mean +/- SEM), 263.7 +/- 60.2 vs. 73.8 +/- 3.1 micrograms/L.h; P less than 0.03] and potentiated the somatotroph response to ivGHRH (inNS with ivGHRH vs. ivGHRH, 1316 +/- 183.0 vs. 644.9 +/- 154.5 micrograms/L.h; P less than 0.03). In group B (n = 6; age, 11.5-15.9 yr) ivGHRH induced a GH rise clearly higher than that induced by inGHRH (604.2 +/- 154.3 vs. 137.1 +/- 28.2 micrograms/L.h; P less than 0.03). Administration of inNS induced a GH rise similar to that occurring after inGHRH (AUC, 239.2 +/- 69.5 micrograms/L.h) and markedly increased the inGHRH-induced GH response (482.4 +/- 103.6 micrograms/L.h; P less than 0.05 and 0.03 vs. inNS and inGHRH, respectively), so that it overlapped with that induced by ivGHRH alone. In conclusion, cholinergic agonists such as neostigmine are able to increase both basal and GHRH-induced GH secretion in short children even when given intranasally. Combined intranasal administration of neostigmine and GHRH (10 micrograms/kg) is able to induce a GH rise similar to that induced by ivGHRH alone (1 microgram/kg), suggesting the potential usefulness of this combination cocktail and route of administration for the treatment of short stature.

Adrenocorticotropin and cortisol hyperresponsiveness to hexarelin in patients with Cushing's disease bearing a pituitary microadenoma, but not in those with macroadenoma.

We previously reported that in Cushing's disease (CD) the ACTH- and cortisol (F)-releasing activity of Hexarelin (HEX), a GH secretagogue, is exaggerated with respect to that in normal subjects and is higher than that of human CRH (hCRH), but it is absent in Cushing's syndrome. Our aim was to extend the study about the effects of HEX (2.0 microg/kg, iv) on ACTH and F secretion in 21 patients with CD (3 men and 18 women, 16-68 yr old). Based on magnetic resonance imaging, 15 CD patients had pituitary microadenoma, and 6 had macroadenoma. The results in CD patients were compared with those in 27 normal age-matched controls (NS; 10 men and 17 women, 24-69 yr old). Basal ACTH and F levels in CD were similar in patients with microadenom (mean+/-SEM, 78.3+/-7.2 pg/mL and 237.1+/-23.6 microg/L, respectively) and macroadenoma (57.4+/-9.0 pg/mL and 196.9+/-20.1 microg/L, respectively) and were higher (P < 0.001) than those in NS (17.7+/-2.0 pg/mL and 115.3+/-6.7 microg/L, respectively). In microadenoma CD patients, HEX induced marked ACTH and F increases (delta peak, mean+/-SEM: 261.2+/-77.6 pg/mL and 226.1+/-87.2 microg/L, respectively), which were higher (P < 0.04) than those induced by hCRH (45.6+/-16.9 pg/mL and 84.6+/-25.7 microg/L, respectively). Moreover, in microadenoma CD patients, the ACTH and F responses to HEX were higher (P < 0.001) than those in NS (18.5+/-4.0 pg/mL and 36.1+/-6.8 microg/L, respectively). In macroadenoma CD patients, HEX induced a slight, but significant increase (P < 0.02) in ACTH and F levels (33.9+/-18.0 pg/mL and 89.6+/-34.3 microg/L, respectively), which was not significantly different from that elicited by hCRH (20.0+/-7.0 pg/mL and 54.8+/-21.3 microg/L, respectively). In macroadenoma CD patients, the ACTH and F responses to HEX and hCRH were, in turn, similar to those in NS. In conclusion, our findings demonstrate that the ACTH and F hyperresponsiveness to HEX is present in Cushing's disease with micro-, but not macro- ACTH-secreting pituitary adenoma. This finding agrees with other evidence pointing toward differences in the hormonal behavior between micro- and ACTH-secreting pituitary macroadenomas.

Effects of octreotide treatment on the proliferation and apoptotic index of GH-secreting pituitary adenomas.

To investigate the effects of octreotide administration on the growth rate of GH-secreting pituitary adenomas, we measured both the Ki-67 labeling index (LI) and the apoptotic index in tumor specimens from octreotide-treated or matched untreated acromegalic patients. Thirty-nine patients who received octreotide until the day of or the day before surgery and 39 untreated patients matched for sex, age, tumor size, extension, and invasiveness were studied. Immunocytochemical analysis was performed on paraffin-embedded material using a monoclonal antibody (MIB-1) directed against a proliferation-associated nuclear antigen, Ki-67, to measure the growth fraction. Apoptosis was assessed by the terminal deoxynucleotidyl transferase-mediated deoxy-UTP nick endlabeling method, using a monoclonal antibody recognizing areas of DNA fragmentation. The Ki-67 LI and apoptosis were counted on separate slides in at least 1000 evaluable cells. Octreotide-treated patients showed a lower Ki-67 LI (1.8 +/- 0.3%) than untreated controls (3.8 +/- 0.7%; P < 0.02). Overall, the mean Ki-67 LI of treated patients was 53% lower than that in untreated patients. The antiproliferative effect of octreotide occurred independently of tumor extension and invasiveness. Octreotide-treated and untreated patients showed similar apoptotic indexes (0.6 +/- 0.2% and 0.8 +/- 0.3%, respectively). There was a positive correlation between the Ki-67 LI and the apoptotic index (r = 0.29; P < 0.03). Our study demonstrates that acromegalic patients receiving chronic octreotide treatment have a lower value of the proliferation marker Ki-67, but no significant difference in the apoptotic index compared with matched untreated patients. The antiproliferative effect of octreotide on GH-secreting adenomas should imply a lower risk of tumor growth during long-term chronic treatment with the drug.

Arginine and growth hormone-releasing hormone restore the blunted growth hormone-releasing activity of hexarelin in elderly subjects.

Although both spontaneous and stimulated GH secretion undergo an age-related decline, the secretory capacity of somatotrope cells is preserved in human aging. In the present study we compared the GH responses to hexarelin, GHRH, and the combined administration of hexarelin and GHRH or arginine in young and elderly subjects. Thirteen young (24- to 30-yr-old) and 16 elderly (65- to 84-yr-old) normal males were divided into 2 groups. The first group (7 young and 8 elderly subjects) received the following as single iv injections during 3 different treatment sessions: hexarelin (2 micrograms/kg), GHRH (2 micrograms/kg), or hexarelin (2 micrograms/kg) plus GHRH (2 micrograms/kg). The second group (6 young and 8 elderly subjects) was administered single iv injections of hexarelin (2 micrograms/kg) or hexarelin (2 micrograms/kg) plus arginine (0.5 g/kg) during 2 different treatment sessions. In both groups basal IGF-I levels in the elderly were lower than those in young subjects (114.5 +/- 18.7 vs. 211.5 +/- 19.1 micrograms/L; P < 0.001). In the first group the GH response to hexarelin was greater in young compared to elderly subjects (area under the curve from 0-120 = 4849 +/- 601 vs. 2112 +/- 683 micrograms.min/L; P < 0.001). GHRH elicited a lower GH response than that induced by hexarelin in both young (1455 +/- 102 micrograms/h.L; P < 0.02) and elderly subjects (563 +/- 87 micrograms/min.L; P < 0.02). GHRH potentiated the somatotrope response to hexarelin in both young (7725 +/- 503 micrograms/min.L; P < 0.02) and elderly subjects (3895 +/- 612 micrograms/min.L; P < 0.02), but to a lesser extent in the latter (P < 0.001). In the second group, the GH response induced by hexarelin was also higher in young subjects than in elderly subjects (4819 +/- 668 vs. 1649 +/- 459 micrograms/min.L; P < 0.001). The GH response to hexarelin was potentiated by arginine in elderly (4139 +/- 1057 micrograms/min. L; P < 0.001), but not in young subjects (4743 +/- 774 micrograms/min.L). This study shows that the maximal effective dose of hexarelin releases more GH than the maximal effective dose of GHRH in both normal young and elderly subjects. The effect of hexarelin on GH secretion is age dependent, and the GH response to the combined administration of hexarelin and GHRH was significantly higher in young subjects compared to elderly subjects. Arginine does not potentiate the GH response to hexarelin in young subjects, whereas it significantly enhances it in elderly subjects.(ABSTRACT TRUNCATED AT 400 WORDS)