Oxytocin enhances the effects of clonidine on blood pressure and locomotoractivity in rats

Oxytocin treatment decreases blood pressure and changes the pattern of spon taneous motor activity. The aim of this study was to explore if alpha 2-adr enoreceptors that are involved in the regulation of blood pressure and spon taneous motor activity are influenced by oxytocin treatment. For this purpo se, male rats were pretreated with oxytocin (1 mg/kg subcutaneously (s.c.)) or saline once a day during 5 days. Clonidine (alpha 2-adrenoreceptor agon ist) decreased blood pressure (2.5 mu g/kg intracerebroventricularly (i.c.v .) and 100 mu g/kg s.c.) and changed spontaneous motor activity (100 mu g/k g s.c.), observed in an open field arena, significantly more in oxytocin pr etreated rats compared to saline pretreated controls (P < 0.05). In contras t, idazoxan (alpha 2-adrenoreceptor antagonist) (50 mu g/kg i.c.v.) caused a significantly smaller elevation of blood pressure in the oxytocin pretrea ted rats (P < 0.05). In addition, the effect on blood pressure of an alpha 1-adrenoreceptor agonist, phenylephrine, was evaluated. It increased blood pressure equally in the oxytocin- and saline pretreated rats. The present s tudy shows that subchronic oxytocin treatment increases the effects of clon idine on blood pressure and spontaneous motor activity in rats. These findi ngs imply that alpha 2-adrenoreceptors are involved in the effects of oxyto cin treatment on blood pressure and spontaneous motor activity. (C) 1999 Pu blished by Elsevier Science B.V. All rights reserved.