Possible mixed agonist--antagonist activity of D-sulpiride at dopamine receptor level in man

The effects of different doses of D-sulpiride (1, 6, 12 and 25 mg, i.v.) on arterial blood pressure (ABP), heart rate (HR) and prolactin (PRL), growth hormone (GH), insulin and gastrin secretions have been studied in 8 normal men. D-Sulpiride increased systolic ABP with a maximum effect rather 12 mg i.v., while it had only slight effects on diastolic ABP and HR. PRL secretion was increased by D-sulpiride in a dose-dependent way, while insulin secretion was lowered and GH secretion slightly enhanced only in a restricted range of doses (6 mg and 12 mg i.v., respectively). Gastrin secretion seemed to be unaffected by D-sulpiride at any of the tested doses. These results are discussed in view of a possible mixed agonist--antagonist activity of D-sulpiride at dopamine receptor level in contrast with the relatively pure antagonistic action of the levo isomer.