EFFECTS OF HOMOLOGOUS ATRIAL, BRAIN, AND C-TYPE NATRIURETIC PEPTIDES ON ISOLATED HEART AND BLOOD-VESSELS OF BULLFROG

The cardiovascular effects of homologous natriuretic peptides (fNPs) w ere examined in the bullfrog, Rana catesbeiana. Synthetic bullfrog atr ial natriuretic (fANP), brain natriuretic (fBNP) and C-type natriureti c peptides (fCNP I and fCNP II), were tested in vitro and compared und er the same experimental conditions. All frog NPs produced a significa nt, and concentration-dependent, reduction in tension (relaxant effect ) in the isolated dorsal aorta. Frog CNP II exhibited similar vasorela xation profile as that of fANP, while fBNP and fCNP I had lower activi ty than fANP. Frog NPs inhibited norepinephrine induced contraction an d fCNP II was most potent. In isolated preparations of atrium and vent ricle, fCNP I and II produced a significant, and concentration-depende nt, reduction in tension, but neither fANP nor fBNP produced any signi ficant effects. Frog CNP II is most potent among fNPs in relation to r educe the cardiac output. Chronotropic responses of the heart to admin istrations of NPs were insignificant. The present results for the firs t time showed that fNPs play roles in the control of cardiovascular sy stem, both blood vessels and heart, in the bullfrog.