PROLACTIN STIMULATION BY INTRAVENOUS LABETALOL IS MEDIATED INSIDE THE CENTRAL NERVOUS SYSTEM

Abstract

Labetalol infusion increases prolactin (PRL) secretion in hypertensive patients. In an attempt to investigate the site where labetalol stimulates PRL, the druy was infused i.v. (100 mg) into healthy subjects, both under basal conditons and after pretreatment with L-dopa plus carbidopa (250 mg and 25 mg respectively every 6 h for 1 day), since this regimen has been reported to blunt the PRL reponses to centrally acting stimuli. The effects of oral labetalol administration (100 and 200 mg) on PRL was also evaluated. Serum PRL concentration did not change after oral labetalol, whereas it was increased by i.v. drug administration. This effect was completely abolished by pretreatment with L-dopa plus carbidopa. These findings, though they do not demonstrate the mechanism, suggest that the hyperprolactinemia induced by labetalol mediated inside the blood-brain barrier.