LACK OF EFFECT OF ATRIOPEPTIN-II ON RABBIT GLOMERULAR ARTERIOLES INVITRO

This study was designed to determine if atriopeptin II (AP II) has any direct action on glomerular arterioles in vitro. Single superficial afferent or efferent arterioles were dissected from rabbit kidney, cannulated with micropipettes, and changes in lumen diameter were measured. The effect of AP II (10-12-10-7 M) was tested alone or in arterioles precontracted with norepinephrine (3 .times. 10-7 M, afferent) or angiotensin II (10-10 M, efferent). By itself, AP II had no effect on lumen diameter in afferent or efferent arterioles, but both arterioles responded to 3 .times. 10-7 M norepinephrine with 74 and 54% reductions in lumen diameter, respectively. Similarly, in norepinephrine-contracted afferent arterioles and angiotensin II-contracted efferent arterioles, AP II did not alter lumen diameter although acetylcholine (10-6 M) produced near maximal relaxation of both arterioles. Furthermore, luminal addition of AP II (10-7 M) had no effect on control lumen diameter or on the response to norepinephrine or angiotensin II. The preparation of AP II was biologically active since it caused dose-dependent increases in guanosine 3'',5''-cyclic monophosphate levels in isolated rat glomeruli. These results suggest that the renal vascular effects of AP II observed in vivo are not due to a direct action on superficial glomerular arterioles but rather to an, as yet, unidentified indirect action of this peptide.