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The effect of a single oral dose of bromocriptine 2.5 mg was evaluated in 11 normotensive and 6 hypertensive volunteers. 150 min after drug administration, a significant decrease in plasma noradrenaline concentration from 202 to 124 pg/ml in normotensive and from 197 to 119 pg/ml in hypertensive patients was observed. Plasma 3,4 dihydroxyphenylacetic acid, a major metabolite of dopamine, fell from 1132 to 956 pg/ml in normal subjects and from 1242 to 807 pg/ml in hypertensives. No change in plasma adrenaline was found. At the same time, mean arterial pressure showed a significant decrease from 90 to 81 and from 132 to 111 mmHg in normotensive and hypertensive subjects, respectively. Bromocriptine also inhibited the increase in noradrena-line level that occurred when the subjects changed from the supine to the standing position. The inhibition was more evident in hypertensive subjects. It is suggested that the hypotensive effect of bromocriptine is mediated by the inhibition of noradrenaline release due to the stimulation of dopamine receptors on noradrenergic nerve terminals. [ABSTRACT FROM AUTHOR]