Dopaminergic control of the rat thyrotroph

The established technique of dynamic perfusion of dispersed rat anterior pituitary cells was used to investigate the role of dopamine in the release of thyroid-stimulating hormone (TSH). The basal release of TSH was 124 +/- 22 ng/ml (mean +/- SEM) and this remained unchanged in the presence of dopamine (5 X 10(-6) M), while basal prolactin release was suppressed to 50% of control values. Perfusion with thyrotrophin-releasing hormone (TRH) in doses between 1.4 X 10(-10) and 22.4 X 10(-10) M produced a consistent and reproducible dose-response curve for TSH (n = 14) which was not significantly altered by the presence of dopamine (n = 5). Perfusion with bromocriptine (10(-6) M), a dopamine agonist, did not alter the basal or stimulated TSH release. No stimulation of TSH release was observed when the cells were challenged with 2-min pulses of domperidone, a dopamine antagonist (2 X 10(-9) to 2 X 10(-5) M). The inclusion of somatostatin-14 (3 X 10(-9) M) in the perfusate inhibited TRH-stimulated TSH release. Our results suggest that, in the rat, dopaminergic inhibition of TSH release does not occur at the level of the pituitary.