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Prostaglandins have been implicated as paracrine regulators of renin secretion, but the specific pathways and receptor(s) carrying out these functions have not been fully elucidated. To examine the contributions of prostanoid synthetic pathways and receptors to regulation of renin in the intact animal, we used a panel of mice with targeted disruption of several key genes: cyclooxygenase-2 (COX-2), microsomal PGE synthases 1 and 2 (mPGES1, mPGES2), EP2 and EP4 receptors for PGE2, and the IP receptor for PGI2. To activate the macula densa signal for renin stimulation, mice were treated with furosemide over 5 days and renin mRNA levels were determined by real-time RT-PCR. At baseline, there were no differences in renin mRNA levels between wild-type and the various strains of mutant mice. Furosemide caused marked stimulation of renin mRNA expression across all groups of wild-type control mice. This response was completely abrogated in the absence of COX-2, but was unaffected in mice lacking mPGES1 or mPGES2. The absence of Gs/cAMP-linked EP2 receptors had no effect on stimulation of renin by furosemide and there was only a modest, insignificant reduction in renin responses in mice lacking the IP receptor. By contrast, renin stimulation in EP4-/- mice was significantly reduced by ∼70% compared with wild-type controls. These data suggest that stimulation of renin by the macula densa mechanism is mediated by PGE2 through a pathway requiring COX-2 and the EP4 receptor, but not EP2 or IP receptors. Surprisingly, mPGES1 or mPGES2 are not required, suggesting other alternative mechanisms for generating PGE2 in response to macula densa stimulation. [ABSTRACT FROM AUTHOR]

During nephrogenesis, renin expression shifts from the vessel walls of interlobular arteries to the terminal portions of afferent arterioles in a wavelike pattern. Since the mechanisms responsible for the developmental deactivation of renin expression are as yet unknown, we hypothesized that the developing renin-angiotensin system (RAS) may downregulate itself via negative feedback to prevent overactivity of renin. To test for a possible role of angiotensin II in the developmental deactivation of renin expression, we studied the development of intrarenal renin expression in mice lacking ANG II AT1a, AT1b, or AT2 receptors and in animals with abolished circulating ANG II due to deletion of the gene for angiotensin 1-converting enzyme (ACE). The development of intrarenal renin expression was normal in mice lacking ANG II AT1b or AT2 receptors. In animals lacking both ANG II AT1a and AT1b receptors, ACE, or ANG II AT1a receptors, renin expression was normal early and renin disappeared from mature vessels until development of cortical interlobular and afferent arterioles began. The development of cortical vessels in these genotypes was accompanied by a markedly increased number of renin-expressing cells, many of which were ectopically located and attached in a grapelike fashion to the outer vessel perimeter. Although the number of renin-expressing cells declined during final maturation of the kidneys, the atypical distribution pattern of renin cells was maintained. These findings suggest that ANG II does not play a central role in the typical developmental shift in renin expression from the arcuate vessels to the afferent arterioles. During postnatal maturation of mouse kidneys, interruption of the RAS causes severe hyperplasia of renin cells via a mechanism that centrally involves AT1a receptors. However, the distribution pattern of renin cells in adult kidneys with an interrupted RAS does not mimic any normal developmental stage since renin expression is frequently found in cells outside the arteriolar vessel walls in RAS mutants. [ABSTRACT FROM AUTHOR]

In the resistance vessels of the renal microcirculation, store- and/or receptor-operated calcium entry contribute to the rise in vascular smooth muscle cell (VSMC) intracellular calcium concentration in response to vasoconstrictor hormones. Short transient receptor potential (TRPC) channels are widely expressed in mammalian tissues and are proposed mediators of voltage-independent cation entry in multiple cell types, including VSMCs. The seven members of the TRPC gene family (TRPC1-7) encode subunit proteins that are thought to form homo- and heterotetrameric channels that are differentially regulated depending on their subunit composition. In the present study, we demonstrate the relative abundance of TRPC mRNA and protein in freshly isolated rat renal resistance vessels, glomeruli, and aorta. TRPC1, 3, 4, 5, and 6 mRNA and protein were detected in both renal resistance vessels and aorta, whereas TRPC2 and TRPC7 mRNA were not expressed. TRPC1, 3, 5, and 6 protein was present in glomeruli. TRPC3 and TRPC6 protein levels were significantly greater in the renal resistance vessels, about six- to eight-fold higher than in aorta. These data suggest that TRPC3 and TRPC6 may play a role in mediating voltage-independent calcium entry in renal resistance vessels that is functionally distinct from that in aorta. [ABSTRACT FROM AUTHOR]

Although L-type voltage-dependent calcium channels play a major role in mediating vascular smooth muscle cell contraction in the renal vasculature, non-L-type calcium entry mechanisms represent a significant component of vasoactive agonist-induced calcium entry in these cells as well. To investigate the role of these non-voltage-dependent calcium entry pathways in the regulation of renal microvascular reactivity, we have characterized the function of store- and receptor-operated channels (SOCs and ROCs) in renal cortical interlobular arteries (ILAs) of rats. Using fura 2-loaded, microdissected ILAs, we find that the L-type channel antagonist nifedipine blocks less than half the rise in intracellular calcium concentration ([Ca(2+)](i)) elicited by norepinephrine. SOCs were activated in these vessels using the sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA) inhibitors cyclopiazonic acid and thapsigargin and were dose dependently blocked by the SOC antagonists Gd(3+) and 2-aminoethoxydiphenyl borate (2-APB) and the combined SOC/ROC antagonist SKF-96365. Gd(3+) had no effect on the non-L-type Ca(2+) entry activated by 1 microM NE. A low concentration of SKF-96365 that did not affect thapsigargin-induced store-operated Ca(2+) entry blocked 60-70% of the NE-induced Ca(2+) entry. Two different calmodulin inhibitors (W-7 and trifluoperazine) also blocked the NE-induced Ca(2+) entry. These data suggest that in addition to L-type channels, NE primarily activates ROCs rather than SOCs in ILAs and that this receptor-operated Ca(2+) entry mechanism is regulated by calmodulin. Interestingly, 2-APB completely blocked the NE-induced non-L-type Ca(2+) entry, implying that SOCs and ROCs in preglomerular resistance vessels share a common molecular structure.

Norepinephrine directly induces growth of the vascular wall, which may involve not only proliferation of smooth muscle cells (SMCs) and adventitial fibroblasts (AFBs) but also augmentation of their migration. To test this hypothesis, growth-arrested SMCs and AFBs from rat aorta were exposed to norepinephrine. Norepinephrine caused dose-dependent migration of both cell types that was dependent on chemotaxis. In contrast, platelet-derived growth factor (PDGF)-BB, used as a positive control, stimulated both chemotaxis and chemokinesis. Only alpha(1D)-adrenoceptors (AR) and alpha(2)-AR antagonists inhibited norepinephrine migration of SMCs, whereas norepinephrine migration of AFBs was only inhibited by alpha(1A)-AR and alpha(1B)-AR antagonists; beta-AR blockade was without effect. Norepinephrine and PDGF-BB were additive for AFB, but not SMC, migration. Stimulation of migration was reversed at high norepinephrine concentrations (10 microM); this inhibition was mediated by alpha(2)- and beta-ARs in AFBs but not in SMCs. Thus norepinephrine induces migration of SMCs and AFBs via different alpha-ARs. This action may participate in wall remodeling and norepinephrine potentiation of injury-induced intimal lesion growth.