[Interaction of atrial natriuretic factor and cicletanine in relation to contractions induced by endothelin and phenylephrine on the isolated rat aorta].

The interaction between cicletanine (CIC) and atrial natriuretic factor (ANF) on vessels was studied using the isolated rat aorta as model. Contractions induced by endothelin (ET1), a vasoconstrictor peptide from vascular endothelial cells, and by phenylephrine (PE), an alpha 1-adrenoceptor agonist, were recorded isometrically on aortic rings the endothelium of which had deliberately been damaged. Both agonists produced a concentration-dependent contraction (ET1:EC50 1.8 nM, Emax 2.2 g; PE:EC50 30 nM, Emax 2.4 g) which was antagonized by a 30 min pretreatment with either CIC (100 microM) or ANF (1 nM). However, PE was more sensitive than ET1 to the inhibitory action of CIC or ANF. Moreover, during inhibition by ANF spasmodic contractions were observed with PE but not with ET1; this was not observed when the antagonist was CIC. The inhibitory effect produced by the combination of CIC and ANF was additive with ET1 whereas a potentiation was observed with PE. Thus, on the isolated rat aorta model the contraction induced by PE was more sensitive to the action of ANF than that induced by ET1, which indicates that the two antagonists have a different mechanism of action. A direct action of CIC on the alpha-adrenoceptor might account for the potentiation observed between ANF and CIC against PE.