Macula densa neuronal nitric oxide synthase.

In the juxtaglomerular apparatus of the kidney the distal tubule returns to its own glomerulus where specialised cells, the macula densa (MD) cells, are located so that they come in contact with the tubular fluid. It is well documented that MD cells sense the distal tubular flow-rate and that when the flow is too high they are activated, which leads to vasoconstriction of the afferent arteriolar, the tubuloglomerular feedback (TGF). Neuronal nitric oxide synthase (nNOS) is largely expressed in the MD cells. Acute inhibition of MD nNOS leads to an enhanced TGF response, indicating that nitric oxide (NO) is an important short-term modulator for volume regulation in the body. By contrast, the NO from the nNOS of the MD cells does not seem to play a role in the long-term adaptations of renin release in low- or high-salt diets.