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Dopamine receptors in intracerebral motor and endocrine systems have been divided into two main types, D-1 and D-2, dependent on the presence or absence of adenylate cyclase linkage. Here we have investigated a number of dopamine agonist and antagonist drugs in man that have different actions on D-1 and D-2 receptors in animals. Motor and endocrine effects in parkinsonian subjects seem to depend on drug interaction with D-2, but not D-1, receptors. These results may have important implications for the design of anti-parkinsonian and antipsychotic agents.

1. Plasma bromocriptine levels following separate oral doses of bromocriptine 12.5, 25, 50 and 100 mg have been determined in ten subjects with parkinsonism. 2. There was considerable variation between peak plasma bromocriptine levels in individual subjects after similar doses of bromocriptine. Peak levels occurred 30–210 min after dosage (mean 102 min). Peak clinical response, peak rise in plasma growth hormone level and fall in blood pressure followed shortly after peak bromocriptine levels occurred. 3. The shape of the plasma‐time curve for bromocriptine was similar with all dosages. 4. There was no significant relationship between peak plasma bromocriptine levels, peak clinical response, peak increase in growth hormone and peak fall in blood pressure. However, the degree of improvement in the signs of parkinsonism was related to plasma bromocriptine levels was achieved. 5. Metoclopramide 60 mg pretreatment had no consistent effect upon plasma bromocriptine levels, the clinical or hormonal response.

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