Dopaminergic Control of the Rat Thyrotroph

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Abstract
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 × 10–6M), while basal prolactin release was suppressed to 50% of control values. Perfusion with thyrotrophin-releasing hormone (TRH) in doses between 1.4 × 10–10 and 22.4 × 10–10M 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 (10–6M), 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 × 10–9 to 2 × 10–5M). The inclusion of somatostatin-14 (3 × 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.