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Glucocorticoids are thought to inhibit growth hormone (GH) secretion through an enhancement of endogenous somatostatin tone. The aim of our study was to evaluate the effect of galanin, a neuropeptide that stimulates GH secretion, on GH-releasing hormone (GHRH)-induced GH secretion in adult patients with nonendocrine diseases who were under daily immunosuppressive glucocorticoid therapy. Six normal subjects (four men, two women) and seven steroid-treated subjects (three men, four women) were studied. GHRH-induced GH secretion was evaluated during a 40-minute intravenous (i.v.) infusion of saline or porcine galanin (12.5 micrograms/min). During saline infusion, steroid-treated patients showed a blunted GH response to GHRH (GH peak, 8.1 +/- 2.8 micrograms/L), as compared with normal subjects (GH peak, 23.8 +/- 3.9 micrograms/L). During galanin infusion, the GH response to GHRH was significantly enhanced (GH peak, 46.6 +/- 9.4 micrograms/L, P less than .05), as compared with saline infusion in normal subjects. In contrast, galanin infusion did not enhance the GH response to GHRH (GH peak, 16.6 +/- 6.5 micrograms/L), as compared with saline infusion in steroid-treated patients. The area under the GH-response curves was also significantly (P less than .05) lower in steroid-treated subjects, as compared with normal subjects. Thus, galanin failed to normalize or enhance the GH response to GHRH in patients treated long-term with glucocorticoids. It can be hypothesized that galanin does not elicit GH secretion by decreasing hypothalamic somatostatin tone.

Short-term studies have shown that octreotide, a long-acting somatostatin analog, blunts postprandial glycemic responses and reduces insulin requirement in insulin treated diabetic patients. The aim of our study was to investigate the effects of three single, different doses of octreotide on the glycemic response to a mixed meal in eight insulin treated type 2 diabetic patients after secondary failure with hypoglycemic agents. Previous treatments were substituted by regular insulin, 0.5 U/kg/day divided into three sc injections, for at least seven days. All patients received: (a) regular insulin (0.1 U/kg, sc) at 7.30 am; (b) octreotide 25 micrograms sc or (c) 50 micrograms sc or (d) 100 micrograms sc simultaneously with insulin but injected at different sites. From 8.00 to 8.15 the patients consumed a preconstituted fluid mixed meal of 250 ml. Following insulin alone a significant increase in blood glucose levels was observed after the meal. Abolished and not significantly different blood glucose responses to the meal after each of the three doses of octreotide were observed. Our findings suggest that with a low dose of octreotide (25 micrograms) it is possible to abolish the postprandial glycemic peak in type 2 diabetic patients treated with insulin.

A single administration of the sex-dependent hepatocarcinogenic beta-blocker DL-1-(2-nitro-3-methyl-phenoxy)3-tert-butylamino-propan-2-ol (DL-ZAMI 1305) induces liver DNA damage, as evaluated by alkaline sucrose gradient analysis, in female but not in male Fisher 344 rats. The shift of the methyl-group from the 3-position of the aromatic ring of DL-ZAMI 1305 to the 4- and 5-position causes the progressive decrease of the genotoxic activity of the molecule. No effect on the DNA-damaging capacity of DL-ZAMI 1305 is instead observed when the NO2 group of the aromatic ring is reduced to an NH2 group. Bis-demethylation of the side chain of DL-ZAMI 1305, or its modification to an alpha-hydroxicarboxylic acid or glycol, increases the DNA-damaging capacity of the molecule, which becomes genotoxic also for the liver of the male rat. Thus, modifications of the chemical structure of the aromatic ring or of the side chain of DL-ZAMI 1305 affect the genotoxic activity of the molecule both in male and female rat liver. The modifications of the side chain of DL-ZAMI 1305 investigated in the present work are likely to occur in vivo as a consequence of the hepatic metabolism of the molecule. Sex-dependent differences in the activity of the liver drug-metabolizing system might explain the different genotoxic and oncogenic activity of DL-ZAMI 1305 in the two sexes.

A single administration of the sex-dependent hepatocarcinogenic β-blocker dl -1-(2-nitro-3-methyl-phenoxy)-3-tert-butylaminopropan-2-ol (DL-ZAMI 1305) induces dose-dependent liver DNA damage, as evaluated by alkaline sucrose gradient analysis, in female but not in male Fisher 344 rats. A single administration of the direct mutagenic epoxide-derivative of DL-ZAMI 1305 3-methyl-2-nitro-1-(2,3-epoxypropoxy)-benzene induces dose-dependent DNA damage in the liver of animals of both sexes. However, also in this case, the genotoxic activity of the compound appears to be significantly higher in female than in male rats. A DNA-damaging capacity similar in the two sexes is instead exerted by DL-ZAMI 1305-unrelated direct mutagens, like N-methyl-N-nitrosourea (MNU) and methyl-methanesulfonate (MMS). The data confirm the sex-dependent susceptibility of rat liver to the genotoxic activity of DL-ZAMI 1305-related molecules, also in the absence of an absolute requirement for a metabolic activation of the compound.

Glucocorticoids have been shown to inhibit GH secretion in normal man when administered in large amounts for several days. The aim of our study was 1. to investigate the acute effects of a single dose of glucocorticoids on GH secretion in normal man; 2. to look at the relationship between the increase in serum cortisol concentration and GH response to the stimuli. Six healthy volunteers received on three occasions in random order an iv injection of GHRH (1–29) NH2, 100 μg, alone or 60 min after oral administration of either 25 or 50 mg of cortisone acetate. Mean stimulated GH levels, GH peak and integrated GH concentration were significantly lower after GHRH plus cortisone 25 mg than after GHRH alone. Mean GH levels at 15 and 30 min after GHRH injection and the peak GH level showed a further decrease after GHRH plus cortisone 50 mg. We conclude that acute administration of pharmacological doses of glucocorticoids is able to inhibit GH response to GHRH, probably through enhancement of endogenous somatostatin release. Moreover, this pharmacological effect of glucocorticoids seems to be dose-dependent and thus directly related to serum cortisol concentrations.

In vitro studies have demonstrated that thyroid hormones can enhance basal and stimulated growth hormone secretion by cultured pituitary cells. However, both in man and in the rat the effects of high thyroid hormone levels on GH secretion are unclear. The aim of our study was to test the GH response to human GHRH in hyperthyroid patients and to evaluate the effects on GH secretion of short- and long-term pharmacological decrease of circulating thyroid hormones. We examined 10 hyperthyroid patients with recent diagnosis of Graves' disease. Twelve healthy volunteers served as controls. All subjects received a bolus iv injection of GHRH(1-29)NH2, 100 μg. Hyperthyroid patients underwent a GHRH test one and three months after starting antithyroid therapy with methimazole, 10 mg/day po. GH levels at 15, 30, 45, 60 min and GH peak after stimulus were significantly lower in hyperthyroid patients than in normal subjects. The GH peak was also delayed in hyperthyroid patients. After one month of methimazole therapy, most of the hyperthyroid patients had thyroid hormone levels in the normal range, but they did not show significant changes in GH levels after GHRH, and the GH peak was again delayed. After three months of therapy with methimazole, the hyperthyroid patients did not show a further significant decrease in serum thyroid hormone levels. However, mean GH levels from 15 to 60 min were significantly increased compared with the control study. The GH peak after GHRH was also earlier than in the pretreatment study. In conclusion, the GH response to GHRH is inhibited and delayed by hyperthyroidism and returns to the normal pattern after long-term euthyroidism has been achieved with methimazole.

The DNA damaging capacity of the sex-dependent hepatocarcinogen beta-blocker DL-1-(2-nitro-3-methyl-phenoxy)-3-tert-butylamino-propan-2-ol (DL-ZAMI 1305) was evaluated in different sex hormonal conditions. A single injection of DL-ZAMI 1305 causes DNA damage in the liver of the female but not the male Wistar rat. When the hormonal environment of the female rat is converted to 'male type' by ovariectomy and 1 week of treatment with testosterone, DNA damage by DL-ZAMI 1305 is completely abolished. On the contrary, in male rats orchiectomy coupled to 17 beta-estradiol administration increases the amount of hepatic DNA damage by DL-ZAMI 1305 to values similar to those observed in intact female rats. DL-ZAMI 1305 induces hepatic DNA damage also when administered to female Sprague-Dawley and Fisher 344 female rats. It is uneffective instead on the male rats of these strains. Moreover, in the female Fisher 344 rat phenobarbital pretreatment reduces the DNA damaging capacity of DL-ZAMI 1305. Our data indicate that the genotoxic activity of DL-ZAMI 1305 depends on the sex-hormonal status of the animal and that this is possibly due to a modulation of the microsomal mixed function oxidase system by sex hormones.