Evidence of altered dopaminergic modulation of Prl, LH, FSH, GH and TSH secretion during chronic partial dopamine receptor blockade in normal women.

In order to study the influence of chronic, partial dopaminergic blockade on pituitary secretion of Prl, TSH, GH, LH and FSH, 8 normally menstruating women were given metoclopramide (MTC, Primperan ) 7.5 mg daily for 4 weeks. Based on weekly measurements of progesterone, all cycles were ovulatory. Prior to and after 4 weeks of drug administration serial measurements of basal hormone levels as well as the acute alterations after 10 mg of MTC iv were assessed during the early follicular phase. Chronic MTC administration significantly increased serum Prl (P less than 0.02), reduced basal levels of LH (P less than 0.02), whereas basal serum concentrations of TSH, GH and FSH were not changed. Before chronic administration iv MTC evoked significant increments in serum Prl (P less than 0.001), TSH (P less than 0.001) and GH (P less than 0.005). The acute TSH increments were significantly (P less than 0.02) diminished after 4 weeks of treatment. The influence of chronic MTC administration on serum LH and TSH levels may be the result of a competitive effect of a stimulatory influence of the dopamine receptor blocker and an opposing inhibitory influence of an increased hypothalamic dopamine activity, evoked by the MTC induced hyperprolactinaemia. Our data favour that the latter mechanism is dominating in normal women, during chronic administration of a low dose of MTC.