THE EFFECT OF INDOMETHACIN AND ENDOTHELIUM DENUDATION ON THE REACTIVITY OF VASCULAR SMOOTH-MUSCLE FROM PREGNANT RATS WITH SALT-INDUCED HYPERTENSION

Objective: The study examined the effects of salt-induced hypertension on vascular contractile responses during pregnancy and the mechanisms of the effects.Methods: Aortic rings from pregnant Wistar rats, fed f or 6 weeks on diets containing 0.3% (control) and 8.0% (test) sodium c hloride were contracted by phenylephrine, 5-hydroxytryptamine, and pot assium chloride, in the presence and absence of either endothelium or 10(-6) M indomethacin. Contractile responses to calcium chloride were also assessed. Results: High salt intake increased the systolic blood pressure of the rats. Rings from the high-salt-fed rats showed enhance d reactivity to phenylephrine, but not to potassium chloride and 5-hyd roxytryptamine. Indomethacin treatment decreased the contractions of r ings from the test rats to phenylephrine, but did not significantly af fect the responses of rings from the control rats. Removal of endothel ium resulted in similar increase in the contractile responses of rings from both groups of rats to phenylephrine but had no effect on respon ses to 5-hydroxytryptamine and potassium chloride. Rings from hyperten sive rats showed significantly increased maximal contractions to calci um chloride when pretreated with phenylephrine but not potassium chlor ide. Contractile responses to phenylephrine in calcium-free medium wer e similar in both groups of rats.Conclusions: The results suggest that the enhanced contractions of aortic rings from pregnant rats with sal t-induced hypertension are related to alterations in adrenergic mechan isms, and are mediated by vasoconstrictor prostaglandin and enhanced c alcium influx through a phenylephrine-activated receptor operated calc ium entry pathway. The capacity to produce endothelium-dependent relax ation appears unaltered in this form of hypertension in pregnancy.