EFFECT OF DOPAMINE AND A DOPAMINE-D-1 RECEPTOR AGONIST ON PULSATILE THYROTROPIN SECRETION IN NORMAL WOMEN

The inhibitory effect of a pharmacological dose of dopamine and the specific dopamine D‐1 receptor agonist fenoldopam on basal and pulsatile TSH secretion was investigated in normal women. The TSH response to fenoldopam and subsequent releasing hormone administration was also studied. Six women received placebo or dopamine infusion (4.0 μg/kg min) for 17 h. After 9 h, blood samples were collected every 10 min between 0800 and 1600 h for measurement of TSH. Eight women received 8‐h (0900‐1700 h) infusions of either fenoldopam (0.5 μg/kg min) or placebo. After 7 h of infusion 10 μg TRH, 5 μg GnRH and 25 CRF was given i.v. Blood samples were collected every 10 min. Dopamine infusion as well as fenoldopam infusion significantly reduced both mean basal TSH secretion and TSH pulse frequency compared with corresponding control infusions (P < 0.05). However, while the effect on TSH pulsatility was comparable (P > 0.05), the percentage decrease in basal TSH levels after 16 h of dopamine infusion was 51±16% (mean±SD) and after 7 h of fenoldopam infusion 19±12% (P < 0.05). Neither of the drugs affected TSH pulse amplitude and fenoldopam did not influence TRH‐stimulated TSH release (P> 0.05). The results suggest that dopamine D‐1 receptors are involved in modulation of TSH pulsatility probably at the hypothalamic level. It is argued that dopaminergic inhibition of basal TSH secretion and TSH pulsatility is predominantly regulated through dopamine D‐2 receptors at the pituitary level, and through D‐1 receptors at the hypothalamic level, respectively. Copyright © 1990, Wiley Blackwell. All rights reserved