Factors controlling the release of renin. A micropuncture study in the cat

Blood was collected by micropuncture from the efferent arteriole and superficial venules of the cat's kidney. Blood samples were also collected from the femoral artery and the renal vein. The blood renin concentrations (ng A1 m1-1 2h-1) in a basal state were 37.2 +/- 3.5 (S.E.M.) (n equal to 60) (artery), 32.5 +/- 5.2 [7] (efferent arteriole), 53.5 +/- 4(116) (superficial venule), 54.2+/- 5.4 (43) (renal vein). The corresponding values after haemorrhase were 389 +/- 98 (21), 345 +/- 115 (6), 963 +/- 208 (37), 907 +/- 290 (17), ng A1 m1-1 2h-1. The efferent arteriolar renin did not differ from that in the artery but the concentrations in superficial venular blood and renal vein were higher than arterial concentration. Thus renin entered the circulation between the efferent arteriole and the superficial venule. The blood renin concentration of different superficial venules at a steady arterial renin concentration varied markedly. Into certain venules there appeared to be little or no renin secretion, into others a marked renin secretion, suggesting a heterogeneity of renin secretion by the different nephrons. When the flow of tubular fluid to the macula densa of a group of nephrons was blocked, the renin concentration fell and was significantly less than the renin concentration in venules draining non blocked nephrons and less than in the renal vein. These results suggest that the juxtaglomerular apparatus of the nephrons do not release renin in a synchronous fashion. The release appears to be episodic and is inhibited when flow to the macula densa is ceased. This implies that a high sodium concentration at the macula densa stimulates renin release.