The effect of lanthanum on renin secretion and renal vasoconstriction

Abstract

Abstract The juxtaglomerular renin producing cells of the afferent arteriole in the kidney are almost certainly derived by modification of arteriolar smooth muscle cells, and this has served as a basis for seeking common features between smooth muscle contraction and renin secretion. It was suggested that the common related factor might be changes in calcium flux so that increase of intracellular ionized calcium led to arterial constriction and inhibition of renin secretion while reduction of calcium led to arterial relaxation and increase of renin secretion. The present paper explores the effects of lanthanum used because of its ability to interfere with calcium flux on renal vasoconstriction and renin release. It was found that lanthanum (10-50 μmol l-1) inhibited the vasoconstriction due to noradrenaline and that the inhibition quickly disappeared on omitting lanathum from the perfusion medium. This was in sharp contrast to the inhibition of renin release by lanthanum, which remained even in the presence of potent stimulators like isoprenaline and glucagon. This inhibition was, however, overcome by the use of EDTA and it is suggested that this might depend on the ability of EDTA to bind with lanthanum and remove it from membrane sites. In similar experiments an attempt was made to correlate renal vasoconstriction and renin release with the distribution of lanthanum within the arteriolar wall and around the juxtaglomerular cells, as shown by electron microscopy. The main con­clusion was that during inhibition of noradrenaline vasoconstriction, lanthanum was widely distributed but that inhibition of renin persisted, when very little, if any lanthanum could be shown around the juxtaglomerular cells. When EDTA removed the lanthanum blockade, there was no lanthanum visible in relation to the juxtaglomerular cells. It is sug­gested that while the evidence is indirect, the hypothesis relating arterial contraction and renin release with calcium flux is supported.