Effect of isoproterenol on blood pressure and heart rate in different phases of the oestrous cycle.

The effects of a beta-adrenergic agonist, 1-isoproterenol, on heart rate and systemic blood pressure were examined in female rats in different phases of the oestrous cycle. In addition, the effect of isoproterenol on the same variables was studied in ovariectomized rats and ovariectomized rats treated with either oestradiol or progesterone. To this end, heart rate and blood pressure were monitored for 10 min after i.v. injection of isoproterenol (80 micrograms/kg). After isoproterenol injection, the heart rate was found to be significantly (p less than 0.05) higher in rats in the prooestrous phase of the cycle than in rats in the metaoestrous phase. Furthermore, isoproterenol induced a significantly (p less than 0.05) greater increase in heart rate in ovariectomized rats treated with oestradiol, than in ovariectomized otherwise nontreated animals or ovariectomized rats treated with progesterone. No difference in blood pressure response to isoproterenol was observed between the groups. The results indicate that oestrogens modify cardiovascular response to a beta-adrenergic stimulator, possibly by affecting beta-adrenergic receptors in the heart.