ATRIAL-NATRIURETIC-PEPTIDE ANTAGONIZES THE CONTRACTILE EFFECT OF ANGIOTENSIN-II IN THE HUMAN UTERINE ARTERY

The regulatory peptides angiotensin II (Ang II) and atrial natriuretic peptide (ANP) are believed to play important roles in the pathogenesi s of pre-eclampsia. The interactions between Ang II, ANP and noradrena line (NA) were studied in vitro on the human uterine artery. Both Ang II and NA contracted the isolated vessel in a concentration-dependent way. At high doses a decrease in the contractile force induced by Aug II but not NA was encountered. ANP inhibited the smooth muscle activit y elicited by Ang II, resulting in a dextroshift of the concentration- response curve, and a decease in both E(max) (the maximum contractile response) and pD(2) (the negative logarithm of the agonist concentrati on inducing 50% of the E(max)) for Ang II. The results might indicate a specific antagonism between Ang II and ANP, probably at the post-rec eptor level. ANP did not induce any significant change in pD(2) of the concentration-response curve for NA. Only at the highest dose of ANP (10(-7) M) was E(max) depressed. Thus, the results only indicate a wea k antagonistic relationship between NA and ANP in the human uterine ar tery.