Nitric macula densa

The macula densa contains a different type of receptor, sensitive to changes in the rate of delivery of sodium or chloride to the distal tubule. Decreases in distal delivery result in stimulation of renin secretion and vice versa. Potential candidates for signal transmission between the macula densa and the juxtaglomerular cells include adenosine, prostaglandins, and nitric oxide. 

The influence of neuronal nitric oxide synthase (nNOS) on renal arteriolar tone has been studied in the perfused juxtamedullary nephron preparation [126]. Superfusion with a specific nNOS inhibitor decreased afferent and efferent arteriolar diameters, and these decreases in arteriolar diameters were prevented by interruption of distal volume dehvery by papillectomy. When volume delivery to the macula densa segment was increased, afferent arteriolar vasoconstrictor responses to the nNOS inhibitor were enhanced, but this effect was again completely prevented after papillectomy. In contrast, the arteriolar diameter responses to a nonselective NOS inhibitor were only attenuated by papillectomy. Specific nNOS inhibition enhanced the efferent arteriolar vasoconstrictor response to ANG II but did not alter the afferent arteriolar vasoconstrictor responsiveness to ANG II. In contrast, non specific NOS inhibition enhanced both afferent and efferent arteriolar vasoconstrictor responses to ANG It. This study demonstrates that the modulating influence of nNOS on afferent arteriolar tone of juxtamedullary nephrons is dependent on distal tubular fluid flow and that nNOS exerts a differential modulatory action on... 

Ito 5, Ren Y Evidence forthe role of nitric oxide in macula densa control of glomerular hemodynamics. J.CIin.Invest 92 1093-1098, 1993... 

Harris RC, Cheng H, Wang J, Zhang M, McKanna JA. Interactions of the renin-angiotensin system and neuronal nitric oxide synthase in regulation of cyclooxygenase-2 in the macula densa. Acta Physiol Scand 2000 168 47-51. 

The influence of neuronal nitric oxide synthase (nNOS) on renal arteriolar tone has been studied in the perfused juxtamedullary nephron preparation [241]. Superfusion with a specific nNOS inhibitor decreased afferent and efferent arteriolar diameters, and these decreases in arteriolar diameters were prevented by interruption of distal volume delivery by papillectomy. When volume delivery to the macula densa segment was increased, afferent arteriolar vasoconstrictor responses to the nNOS inhibitor were enhanced. 

Mundel, P., Bachmann, S., Bader, M., Fischer, A., Kummer, W., Mayer, B., and Kriz, W. (1992). Expression of nitric oxide synthase in kidney macula densa cells. Kidney Int. 42, 1017-1019. 

Wilcox, C. S., Welch, W. J., Murad, F., Gross, S. S., Taylor, G., Levi, R., and Schmidt, H. FI. (1992). Nitric oxide synthase in macula densa regulates glomerular capillary pressure. Proc. Natl. Acad. Sci. U.S.A. 89, 11993-11997. 

Production of NO and its contribution to the development of renal I-R injury and associated ARF has been investigated and reviewed. NO, produced by nitric oxide synthase (NOS) plays an important role in renal function, both under normal and pathophysiolc cal conditions.The three isofbrms of NOS have been located in the kidney the endothelial and neuronal (constitutive) isofbrms have been identified in the renal vasculature and macula densa, respectively and inducible NOS (iNOS) can be induced in the kidney by qnokines... 

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