Renin secretion is increased by all except
Correct Answer: Sympathetic nerve stimulation
Description: Several different factors regulate renin secretion, and the rate of renin secretion at any given time is determined by the summed activity of these factors. One factor is an intrarenal baroreceptor mechanism that causes renin secretion to decrease when aeriolar pressure at the level of the JG cells increases and to increase when aeriolar pressure at this level falls. Another renin-regulating sensor is in the macula densa. Renin secretion is inversely propoional to the amount of Na+ and Cl- entering the distal renal tubules from the loop of Henle. Presumably, these electrolytes enter the macula densa cells the Na-K-2Cl- transpoers in their apical membranes and the increase in some fashion triggers a signal that decreases renin secretion in the juxtaglomerular cells in the adjacent afferent aerioles. A possible mediator is NO, but the identity of the signal remains unsettled. Renin secretion also varies inversely with the plasma K+ level, but the effect of K+ appears to be mediated by the changes it produces in Na+ and Cl- delivery to the macula densa. Angiotensin II feeds back to inhibit renin secretion by a direct action on the JG cells. Vasopressin also inhibits renin secretion in vitro and in vivo, although there is some debate about whether it&;s in vivo effect is direct or indirect. Finally, increased activity of the sympathetic nervous system increases renin secretion. The increase is mediated both by increased circulating catecholamines and by norepinephrine secreted by postganglionic renal sympathetic nerves. The catecholamines act mainly on b1-adrenergic receptors on the JG cells and renin release is mediated by an increase in intracellular cAMP. The principal conditions that increase renin venous pressure, which triggers an increase in sympathetic activity, and some also decrease renal aeriolar pressure . Renal aery constriction and constriction of the aoa proximal to the renal aeries produces a decrease in renal aeriolar pressure. Psychologic stimuli increase the activity of the renal nerves. Ref: Ganong&;s review of medical physiology,23rd edition,page no: 673, 674
Category:
Physiology
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