L. Devilla

EFFECT OF METOCLOPRAMIDE ON SERUM PROLACTIN LEVELS IN HUMANS

The effect of acute and chronic administration of metoclopramide on serum prolactin levels in normal subjects was studied. Metoclopramide 10 mg i.v. induced a prompt rise in serum prolactin levels in all subjects. At 180 min the levels remained high. Prolactin levels were markedly elevated during a 5 day course of treatment with metoclopramide in six subjects. It is suggested that metoclopramide could be used in the functional exploration of the hypothalamic‐pituitary axis.

INHIBITION OF LACTATION AND INHIBITION OF PROLACTIN RELEASE AFTER MECHANICAL BREAST STIMULATION IN PUERPERAL WOMEN GIVEN TAMOXIFEN OR PLACEBO

Tamoxifen was given orally to 60 puerperal women to inhibit lactation. Twenty control puerperal women were given placebo. Fifteen women receiving tamoxifen and 15 women receiving placebo were studied before, during and after the use of a breast pump under basal conditions and after five days of treatment. Tamoxifen was effective in inhibiting lactation; no rebound phenomena were observed. Its administration was free from side effects. This drug was capable of preventing the prolactin release induced by mechanical breast stimulation. Placebo failed to inhibit lactation and had no effect on prolactin release induced by the use of a breast pump.

Morphine-Induced TSH Release in Normal and Hypothyroid Subjects

The effects of morphine (10 mg i.v.), an opioid agonist, and of naloxone (10 mg i.v.), an opioid antagonist, on serum levels of TSH and PRL were studied in 7 hypothyroid patients and in 5 normal volunteers. Morphine administration induced a prompt, significant increase in serum TSH and PRL in all subjects. The degree of PRL release after morphine was similar in the two groups, while, as regards TSH, the increase was more evident in hypothyroid subjects. Pretreatment with naloxone (4 mg i.v. 5 min before morphine administration) blocked these effects in all subjects. In contrast, naloxone alone was not able to affect significantly TSH and PRL secretion. Moreover, in 5 other euthyroid volunteers, morphine significantly enhanced the response of TSH and PRL to TRH stimulation (200 micrograms i.v.). These data demonstrate that morphine exerts a stimulatory action on TSH and PRL secretion: the possible mode of action of this drug and the physiologic significance of these findings are discussed.

Effect of clomiphene citrate on plasma levels of immunoreactive luteinizing hormone-releasing hormone, gonadotropin, and testosterone in normal subjects and in patients with idiopathic oligospermia.

The effect of clomiphene citrate on plasma immunoreactive luteinizing hormone-releasing hormone (LH-RH), gonadotropin, and testosterone levels was investigated in 10 patients with idiopathic oligospermia and in 10 normal volunteers. A daily 100-mg dose of clomiphene citrate induced a marked, significant increase in plasma immunoreactive LH-RH levels, followed by significant increments in gonadotropin and testosterone values. No significant differences were detected in LH-RH, gonadotropin, and testosterone levels between controls and patients with oligospermia either under basal conditions or during clomiphene treatment.

Dynamic evaluation of prolactin secretion in patients with oligospermia: effects of treatment with metergoline.

Serum prolactin levels were measured in 50 patients with oligospermia and in 20 control subjects under fasting conditions and following the administration of levodopa, pyridoxine, metoclopramide, and synthetic thyrotropin-releasing hormone. Four patients (8%) under fasting conditions had prolactin levels slightly above the normal range. However, no significant differences in prolactin behavior were detected between patients with hyperprolactinemia, patients with normal prolactin levels, and control subjects. The four patients with hyperprolactinemia were treated with metergoline, an ergoline derivative. Metergoline administration promptly reduced the prolactin levels. Spermatogenesis was restored in three patients after 4 to 5 months of treatment.

EFFECT OF PIMOZIDE ON LEVODOPA‐INDUCED GROWTH HORMONE RELEASE IN MAN

SUMMARY. Serum growth hormone (GH) behaviour after levodopa administration was measured in twelve healthy subjects both in basal conditions and after a 4 day course of pimozide (4 mg daily), a specific blocker of dopamine (DA) receptors. In addition, fasting plasma GH was measured on the first, second and third day of treatment. No significant difference was found between GH response to levodopa in basal conditions and after pimozide; moreover, fasting GH was uninfluenced by pimozide.

Effect of dopaminergic blockade on the secretion of growth hormone and prolactin in man

Serum growth hormone (GH) response to insulin and glucagon administration was studied in 12 male and 12 female volunteers under control conditions, and under treatment with pimozide and metoclopramide. In addition, serum prolactin levels were measured during the treatment period. Pimozide and metoclopramide administration had no effect on the GH response to insulin and glucagon. In contrast, serum prolactin levels increased markedly during the treatment period. Dopaminergic blockade is unable to affect GH secretion in response to insulin and glucagon administration in man.

Inhibition of prolactin secretion by nomifensine in man.

Serum prolactin, TSH and GH levels were measured in thirty healthy volunteers in fasting conditions and following oral administration of 200 mg nomifensine. In addition, the effect of the drug on serum prolactin and TSH response to synthetic TRH was studied in twenty normal subjects. Inhibition of endogenous catecholamine reuptake by nomifensine significantly inhibited prolactin release whereas it had no effect on TSH and GH levels. Nomifensine administration had no appreciable effect on the TRH‐induced release of TSH and prolactin.

METERGOLINE INHIBITION OF THYROTROPHIN AND PROLACTIN SECRETIONS IN PRIMARY HYPOTHYROIDISM

The effect of acute oral administration of metergoline on serum thyrotrophin and prolactin levels in six patients with primary hypothyroidism was studied. Metergoline 4mg by mouth caused a significant decrease in the concentration of serum thyrotrophin and prolactin in all subjects. There was no consistent change in serum thyroxine and triiodothyronine concentrations during the experiment. These findings suggest that metergoline inhibits prolactin and thyrotrophin secretion by a direct action on the hypothalamus or pituitary gland.

Suppression of human growth hormone secretion by cyproheptadine.

In order to determine whether or not a serotoninergic mechanism is involved in the secretion of the growth hormone (GH), a study was made of the effect of cyproheptadine, an antiserotonin agent, on plasma GH levels in normal children. The oral administration of cyproheptadine (12 mg daily) reduced GH responses to both L-dopa and glucagon; similarly, the mean GH response to oral glucose administration was significantly reduced after cyproheptadine administration. Plasma glucose values during the tests were not altered by cyproheptadine therapy. These results suggest that the serotoninergic mechanism might be involved in L-dopa-, glucagon-, and glucose-induced GH release.