THE MECHANISM OF RELAXATION IN RESPONSE TO MAGNESIUM BY THE AORTA OF PREGNANT RATS WITH SALT-INDUCED HYPERTENSION

The study examined the effect of sail-induced hypertension on vascular relaxation in response to magnesium sulphate during pregnancy. Pregna nt Wistar rats were fed for 6 weeks on a diet containing 0.3 % (contro l) and 8.0% (test) sodium chloride. Aortic rings were then removed and contracted with 10(-7) M phenylephrine or 30 mM potassium chloride. H igh salt intake increased the systolic blood pressure of the rats and increased the relaxation of phenylephrine-contracted intact rings in r esponse to magnesium sulphate. Neither endothelium removal nor treatme nt with 10(-6) M indomethacin altered the relaxation of rings from the two groups of rats, when contracted with potassium chloride. Both pro cesses significantly (P < 0.05) and similarly decreased the sensitivit y and the maximal relaxation of rings from test rats contracted with p henylephrine; the relaxation of rings from the control rats was not al tered. The results suggest that the relaxation of isolated rat aortic rings contracted with phenylephrine is enhanced in pregnant rats with salt-induced hypertension. The mechanism involved in this enhancement is dependent on the vascular endothelium and receptor activation, and is indomethacin sensitive.