Macula Densa Control of Renin Secretion and Proximal Tubular Pressure
Early studies suggested that the proximal tubular pressure was regulated by a negative feedback mechanism operating via the juxtaglomerular (JG) apparatus, involving changes in renin secretion. Subsequent and recent studies have confirmed this hypothesis. The tubuloglomerular feedback (TGF) response oscillates with a frequency of about 30 mHz, and is sensitive to changes in late proximal flow of less than 3 nl.min−1. It is specifically abolished by loop diuretics. Micropuncture studies have shown that single nephron renin release is increased when Henle loop flow is decreased and conversely, that single nephron renin release is decreased when Henle loop flow is increased. Studies on isolated JG-apparatuses have shown that this is due to the flow-dependent changes in luminal sodium chloride concentration at the level of the macula densa (M.D.). Thus, both the TGF-mediated afferent vasoconstriction and the M.D.-mediated renin secretion share the same luminal signal. The intracellular (i.c.) signal is probably also the same, since an increase in i.c. calcium causes vasoconstriction and inhibition of renin release from the JG cells. Both responses may therefore be considered as part of the TGF-mechanism.
KeywordsLoop Diuretic Renin Release Renin Secretion Oncotic Pressure Efferent Arteriole
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