<P> Renin can be referred to as a hormone even though it has no peripheral receptors and rather has an enzymatic activity with which it hydrolyzes angiotensinogen to angiotensin I . </P> <P> The primary structure of renin precursor consists of 406 amino acids with a pre - and a pro-segment carrying 20 and 46 amino acids, respectively . Mature renin contains 340 amino acids and has a mass of 37 kDa . </P> <P> The enzyme renin is secreted by pericytes (mural cells) (1) in vicinity of the afferent arterioles and similar microvessels of the kidney from specialized cells of the juxtaglomerular apparatus--the juxtaglomerular cells, in response to three stimuli: </P> <Ol> <Li> A decrease in arterial blood pressure (that could be related to a decrease in blood volume) as detected by baroreceptors (pressure - sensitive cells). This is the most direct causal link between blood pressure and renin secretion (the other two methods operate via longer pathways). </Li> <Li> A decrease in sodium load delivered to the distal tubule . This load is measured by the macula densa of the juxtaglomerular apparatus . </Li> <Li> Sympathetic nervous system activity, which also controls blood pressure, acting through the β adrenergic receptors . </Li> </Ol>

Where is the majority of the renin produced in the kidney