1. The effect of low-dose dopamine infusion on anterior pituitary hormone secretion in a group of seven healthy female subjects is reported. Subjects were infused with NaCl solution (154 mmol/l) (control) or dopamine (0.01 and 0.1 μg min−1 kg−1 for 120 min at each rate) on separate days in the early follicular phase of consecutive menstrual cycles.

2. Serum prolactin decreased during infusion of dopamine at 0.01 μg min−1 kg−1 but a similar fall was found in the control group.

3. When the rate of dopamine infusion was increased to 0.1 μg min−1 kg−1 a further substantial decrease in prolactin concentration occurred, whereas prolactin in the control group showed no change. At the end of the period of dopamine infusion at 0.1 μg min−1 kg−1 serum prolactin remained significantly (P<0.025) lower than in the control group (85 ± 12 vs 180 ± 21 m-units/l).

4. No change in thyrotrophin (TSH), growth hormone (GH) or luteinizing hormone (LH) was seen during either rate of dopamine infusion compared with control.

5. While dopamine infusion at 0.1 μg min−1 kg−1 caused significant inhibition of prolactin secretion in normal female subjects, other pituitary hormone secretion was not affected: it is suggested that under the conditions of this study dopamine in hypophysial portal blood is not of primary importance in the control of basal TSH, GH and LH release.

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