Effect of metergoline on the diurnal prolactin responses to insulin-induced hypoglycemia in normal men

Effect of ritanserin, specific 5HT-2 antagonist, on PRL secretion in normal subjects and in different hyperprolactinaemic conditions

The availability of a new specific anti 5HT-2 compound, ritanserin (RTS), led us to further investigate the role of serotonin in controlling PRL secretion. The drug was administered to normoprolactinaemic subjects and to patients with differing hyperprolactinaemic conditions. While RTS failed to modify PRL levels in normoprolactinaemic subjects and in patients with PRL-secreting pituitary adenomas, a marked decrease in the hormone was obtained in patients with functional and puerperal hyperprolactinaemia. The lack of effect of RTS in PRL-secreting pituitary adenomas suggests that the reported suppression of PRL by other antiserotoninergic drugs, such as metergoline, is probably due to their concomitant dopaminergic activity.

Effect of hypoglycaemia, TRH and levodopa on plasma growth hormone, prolactin, thyrotropin and cortisol in Parkinson's disease before and during therapy

Thirteen drug-free and not severely affected patients with idiopathic Parkinson's disease underwent an insulin-hypoglycaemia test, a TRH test and a levodopa test. The responses of growth hormone, prolactin, cortisol and thyrotropin were measured, and retested under stable therapy with levodopa and benserazide. Mean basal and stimulated hormonal concentrations were in the normal range before and during therapy. Minor abnormalities were observed in individual cases, but did not indicate a hypothalamic dopamine deficit.

Effect of benztropine on the diurnal prolactin responses to haloperidol

Prolactin (PRL) responses to haloperidol were investigated at 0900 and 1800 h in six young healthy men under basal conditions and after benztropine mesylate administration. Haloperidol administration induced significantly higher PRL release during the evening compared to the morning. The anticholinergic drug, benztropine, potentiated the PRL responses to haloperidol both in the morning and in the evening. The possible mechanisms of these findings are discussed.

Effect of atropine on the diurnal PRL responses to TRH in normal subjects

Prolactin (PRL) responses to TRH were investigated at 0900 and 1800 hr in six young healthy men under basal conditions and after atropine administration. TRH induced significantly higher PRL release during the evening administration compared to the morning. Atropine had no effect on basal PRL secretion. Unlike the reported influences of anticholinergic drugs on the diurnal PRL responses to other stimuli, atropine also had no effect on TRH-stimulated PRL release either in the morning or in the evening. These observations in part may be accounted for by the direct PRL-releasing effect of TRH (without neurotransmitter involvement).