Effect of captopril on intrarenal blood flow

The inhibition of the renin-angiotensin system by captopril was used in pentobarbital-anesthetized dogs to confirm that the vasoconstrictive action of endorenally synthesized angiotensin II predominates on the efferent glomerular arteriole. Ozolinone is a loop diuretic with two isomers. Only (-)- ozolinone is diuretic, whereas both isomers have a renal vasodilatory effect which predominates on the efferent glomerular arteriole. Only the diuretic isomer increases renin release. The renin hypersecretion is simultaneous with recovery from the initial fall in filtration fraction, because of postglomerular vasodilatation. This recovery does not occur with (+)- ozolinone and is inhibited by pretreatment with captopril. This confirms that vasoconstrictive action of angiotensin II predominates on the efferent glomerular arteriole. Such a vasoconstrictive effect might affect blood flow in the vasa recta, which arise from the efferent arterioles of juxtamedullary glomeruli. This action might enable the renin-angiotensin system to participate in the control of renal medullary blood flow and urinary concentration.