Interaction between morphine, an opioid agonist, and clonidine, an alpha-adrenergic agonist, on the regulation of anterior pituitary hormone secretion in normal male subjects.

In order to investigate the possible interaction between opioid system and noradrenergic system in the regulation of pituitary hormone secretion, the effects of morphine (an opioid agonist, 10 mg i. v.), clonidine (an alpha-adrenergic agonist, infusion of 0.3 mg in 15 minutes) and clonidine + morphine (infusion of the same dose of clonidine beginning 30 minutes before morphine 10 mg i.v.) on anterior pituitary hormone secretion were studied in six normal male volunteers. Morphine alone induced both an increase in TSH and PRL serum levels and a decrease in cortisol serum levels with no changes in GH serum levels. On the contrary clonidine was able to increase GH and TSH levels and to decrease cortisol levels; PRL secretion was not affected. As regards interaction between morphine and clonidine we observed that morphine-induced increase in PRL release was potentiated by clonidine pretreatment; as regards TSH secretion its increase was greater after the administration of the two drugs with respect to the effect of the single drugs. This study, in agreement with our previous data concerning LH secretion, confirms the important link between clonidine and opioid system in neuroendocrine function, too; the possible explanations of our data are discussed.

Evaluation of the effects induced by four opiate drugs, with different affinities to opioid receptor subtypes, on anterior pituitary LH, TSH, PRL and GH secretion and on cortisol secretion in normal men.

In order to ascertain the subtype(s) of opioid receptors involved in the control of pituitary function the effects of four different opiate drugs (morphine, pentazocine, nalorphine and buprenorphine) were studied in four groups of six normal male volunteers. Each of the drugs tested induced, with varying degrees, both a significant increase in PRL and a significant decrease in LH and cortisol. On the contrary TSH secretion was stimulated by buprenorphine and morphine only and GH by nalorphine only. FSH did not change significantly after administration of any drug. Taking into account the different affinities of the drugs used by us for the different opioid receptors, our data do not allow to demonstrate a well-defined correlation between subtypes of opioid receptors and the control of pituitary hormone secretion. The possible explanations of this fact are discussed.

Blunted response of serum aldosterone to metoclopramide in the male elderly.

Serum aldosterone values were determined in 6 elderly (70-82 years) and in 6 adult (31-43 years) male subjects after the intravenous administration of 10 mg of metoclopramide. A significant difference in the metoclopramide-induced serum aldosterone rise was found between the two groups, it being blunted in the older subjects (serum aldosterone peak values: 15.8 +/- 3.6 ng/dl and 38.7 +/- 4.9 ng/dl in elderly and in adult subjects, respectively). The existence of an impaired aldosterone secretion in response to dopaminergic blockade in the elderly is postulated.