Adenosine is a determinant of metabolic control of organ function increasing oxygen supply through the A2 class of adenosine receptors and reducing oxygen demand through A1 adenosine receptors (A1AR). In the kidney, activation of A1AR in afferent glomerular arterioles has been suggested to contribute to tubuloglomerular feedback (TGF), the vasoconstriction elicited by elevations in [NaCl] in the macula densa region of the nephron. To further elucidate the role of A1AR in TGF, we have generated mice in which the entire A1AR coding sequence was deleted by homologous recombination. Homozygous A1AR mutants that do not express A1AR mRNA transcripts and do not respond to A1AR agonists are viable and without gross anatomical abnormalities. Plasma and urinary electrolytes were not different between genotypes. Likewise, arterial blood pressure, heart rates, and glomerular filtration rates were indistinguishable between A1AR ؉/؉ , A1AR

Prostanoids derived from endogenous cylooxygenase (COX)-mediated arachidonic acid metabolism play important roles in the maintenance of renal blood flow and salt and water homeostasis. The relative importance of COX-1 and COX-2 isoforms is under active investigation. We have performed a comprehensive histochemical analysis by comparing rat and mouse kidneys for cellular and subcellular localization of COX-1 and -2 and microsomal-type PGE synthase (PGES), the rate-limiting biosynthetic enzyme in PGE2 synthesis. A choice of different sera was compared, and the results were confirmed by antigen-retrieval techniques, in situ hybridization, RT-PCR, and the use of COX knockout mice. In the glomerulus, significant COX-1 expression was detected in a subset of mesangial cells. Along the renal tubule, the known COX-2 expression in cTAL and macula densa was paralleled by PGES staining. In the terminal distal convoluted tubule, connecting tubule, and cortical and medullary collecting ducts, a significant COX-1 signal was colocalized with PGES; COX-2 was not found in these sites. Intercalated cells were generally negative. Cortical fibroblasts were COX-1 and PGES positive in mice, whereas in rats only PGES could be reliably detected. Lipid-laden interstitial cells of the inner medulla were COX-1, -2, and PGES positive. Vascular smooth muscle cells were not stained. The present data support prominent functions of renal prostanoids, predominantly PGE2, by defining expression sites of the key enzymes for their biosynthesis in the rat and mouse. Results define the renal cell types involved in prostaglandin autacoid functions within spatially restricted sites such as the juxtaglomerular apparatus, mesangium, distal convolutions and collecting duct, and in compartments of the renal interstitium.

It is well established that cyclooxygenase-2 (COX-2) and the neuronal form of nitric oxide synthase (nNOS) are coexpressed in macula densa cells and that the expression of both enzymes is stimulated in a number of high-renin states. To further explore the role of nNOS and COX-2 in renin secretion, we determined plasma renin activity in mice deficient in nNOS or COX-2. Plasma renin activity was significantly reduced in nNOS -/- mice on a mixed genetic background and in COX-2 -/- mice on either BALB/c or C57/BL6 congenic backgrounds. In additional studies, we accumulated evidence to show an inhibitory influence of PGE(2) on nNOS expression. In a cultured macula densa cell line, PGE(2) significantly reduced nNOS mRNA expression, as quantified by real-time RT-PCR. In COX-2 -/- mice, nNOS mRNA expression in the kidney, determined by real-time RT-PCR, was upregulated throughout the postnatal periods, ranging from postnatal day (PND) 3 to PND 60. The induction of nNOS protein expression and NOS activity in COX-2 -/- mice was localized to macula densa cells using immunohistochemistry and NADPH-diaphorase staining methods, respectively. Therefore, these findings reveal that the absence of either COX-2 or nNOS is associated with suppressed renin secretion. Furthermore, the inhibitory effect of PGE(2) on nNOS mRNA expression indicates a novel interaction between NO and prostaglandin-mediated pathways of renin regulation.

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