| Abstract: | Since dopamine (DA) has been implicated in the inhibitory control of both TSH and LH, we have compared TSH and LH levels following dopamine (DA) receptor blockade with domperidone in patients with hyperprolactinemia due to presumed prolactinomas. Eight euthyroid patients (aged 19-37 yr) with presumed prolactinomas each received domperidone (10 mg iv) at 11:00 and 23:00 h and tests were separated by at least one week. Basal TSH levels were significantly greater at 23:00 than at 11:00 h (2.7 +/- 0.5 vs 1.7 +/- 0.4 mU/l, mean +/- SE, p less than 0.01) whereas basal LH levels did not differ. All subjects showed clear rises in basal TSH levels following drug administration and these were significantly greater at 23:00 than at 11:00 h (p less than 0.02 at each time point). In contrast there was no alteration in LH levels following drug administration at either time of day. These data suggest that the mechanisms underlying the dopaminergic control of TSH and LH are different in these patients. Furthermore the data argue against an anterior pituitary or median eminence site of action of DA in the inhibition of LH release in hyperprolactinemia since domperidone does not penetrate the blood brain barrier to any appreciable extent. |
