Frog aorta: An experimental tool for study of action of angiotensin II

Angiotensin II (A-II) produces contraction of isolated vascular smooth muscle preparations obtained from rat, guinea-pig, rabbit and other animals, but reports about effects of A-II on amphibian vascular smooth muscles are lacking. In this study the effects of A-II and its antagonists saralasin and losartan were studied on isolated frog aortic strips. The preparation was very sensitive to A-II. Saralasin in concentrations of 5.48 × 10-7 M, 1.64 × 10-6 M and 5.48 × 10-6 M shifted dose response curve of A-II to the right in a non-parallel manner with a pA2 value of 5.48 and Schild plot having a slope of 0.57 suggesting non-competitive type of antagonism. Losartan in concentrations of 1.08 × 10-12 M, 2.16 × 10-12 M, 4.33 × 10-12 M and 8.67 × 10-12 M inhibited submaximal contractile responses of A-II and pA2 value was 12.02 with Schild plot having a slope of 1.7 indicating competitive type of antagonism. Results of our study showed that frog aorta is a good and stable preparation for study of A-II responses.