1. Central dopaminergic pathways are possibly related to noradrenergic tone and may be important in the pathogenesis of essential hypertension. Basal plasma prolactin levels have been used as a marker of dopaminergic activity in the hypothalamus. The prolactin response to thyrotropin-releasing hormone (TRH) gives evidence of the dynamics of prolactin secretion.
2. To evaluate further the role of dopaminergic mechanisms in hypertension three groups of young male hypertensive patients were studied and compared with healthy male volunteers. In group 1 prolactin secretion was evaluated overnight at 60 min intervals from 22.00 to 06.00 hours. In group 2 we measured plasma prolactin concentrations before and sequentially after intravenous injection of 200 μg of TRH. In group 3 we measured prolactin, plasma and urinary noradrenaline and normetadrenaline during various degrees of physical and mental activity.
3. Basal prolactin, noradrenaline and normetadrenaline levels were higher in the hypertensive patients as compared with normotensive controls. In the hypertensive patients the prolactin response to TRH was significantly attenuated. Treatment with bromocriptine, a centrally acting dopaminergic agonist, lowered the blood pressure and suppressed the elevated prolactin and noradrenaline levels in the hypertensive patients. During bromocriptine therapy the prolactin response to TRH was not different in normotensive and hypertensive subjects.
4. These results suggest an abnormal regulation of the prolactin secretion in young hypertensive patients with evidence of increased sympathetic tone, supporting the concept that central dopaminergic mechanisms may be involved in the development or maintenance of essential hypertension.