Differential cardiovascular responses to oxytocin in male and female rats; influence of platelet activating factor

Oxytocin, a posterior pituitary hormone, is also synthesized in the heart and blood vessels. This signifies its importance in cardiovascular regulation. Sexual dimorphism in cardiovascular responses to oxytocin has been reported in hypertensive animals. We intended to investigate the importance of lipid mediators like the platelet activating factor (PAF) in the cardiovascular responses to oxytocin in male and female rats. Animals were pretreated with platelet activating factor antagonists, WEB 2086 (20 mg/kg) or Ginkgo Biloba (60 mg/kg), and vascular and heart rate responses to oxytocin were ascertained. The results of this study show that pre-treatment with WEB 2086 or Ginkgo Biloba attenuated the vasoconstriction in hindquarters mediated by oxytocin in male and female rats, i.e. a decrease in flow rate from 40.31% (P < 0.01) to 15.58% and 11.41% in females, respectively, while the modification in males was much less, i.e. from 19.15 % (P < 0.05) to 13.39% and 4.49%, respectively. In the other groups of animals utilized for estimation of heart rate, pre-treatment with WEB 2086 (20 mg/kg i.v.) or Ginkgo Biloba (60 mg/kg i.v.) elicited similar results, i.e. enhanced decrease by oxytocin in heart rate from control level in females, demonstrating that in female animals there was potentiated decrease of 18.67% (P < 0.01) and 12.74% (P < 0.05) in the heart rate from control value as compared to the male rats which displayed a mild increase in heart rate. This study suggests that inhibition of PAF unmasks sexually dimorphic cardiovascular responses to oxytocin.