Comparison of ANG II-mediated Ca2+i, IP3 Production and ATPi in Isolated Renal Proximal Convoluted Tubules of Adult SHR and WKY / 대한신장학회잡지

BACKGROUND: The renin angiotensin syaimstem plays an important role in hypertension. Therefore, the purpose of this study was to investigate the comparison of responsiveness to angiotensin II (ANG II) in isolated renal proximal convoluted tubules of spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats. METHODS: Intracellualr calcium concentration ([Ca2+i) was measured using Fura- 2/AM, inositol trisphosphate (IP3) accumulation was determined by radioimmuno assay and cellular ATP content measured using the microchemilunescene method in renal proximal tubule suspension or isolated renal proximal tubules. RESULTS: When measured the ANG II-induced [Ca2+i, the young rats showed a greater response to ANG II than adult rats in both strains. The ANG II (10-7 M)-induced [Ca2+i transient in the cortical tubule suspension from adult SHR was significantly lower than that in age-matched WKY. In isolated proximal tubule segments, ANG II-induced [Ca2+i increment was only observed in S1 segments. Comparing responsiveness to ANG II in SHR and WKY, similar phenomenon was observed as experiment using tubule suspension. IP3 accumulation by ANG II also attenuated in adult SHR. The 20-minutes incubation without any exogenous substrate in proximal convoluted tubule (S1) significantly decreased cellular ATP content and ANG II (10-7 M) inhibited decrement of cellular ATP level. The effect of ANG II on cellular ATP restoration was disappeared by the treatment with losartan. CONCLUSION: From these results, the responsiveness of ANG II to AT1A receptor is attenuated in the proximal convoluted tubules of adult SHR comparing the age- mached WKY.

Distribution of the Dopamine D1 and D2 Receptor Protein Using Immunohistochemistry in Wistar-Kyoto Rat (WKY) and Spontaneously Hypertensive Rat (SHR) Kidneys / 대한신장학회잡지

The kidney and balances of fluid and volume are the basic components of bloocl pressure control, and the kidney is the primary site that initiates the hypertensive process and is affected by hypertensive vascular disease. In the kidney, the dopamine is a potent natriuretic and vasodilating agent, participat- ing in renal sodium excretion and maintenance of cardiovascular homeostasis. And the dopamine receptors in central nervous system and peripheral organs were identified by physiological, biochernical and radioligand binding techniques. Rut previous morphological and biochemical studies have been unable to characterize or determine the tissue distribution of the dopamine receptor subtypes because no selective ligands are available yet. Furthermore, the cellular distribution of the dopamine receptor subtypes in the rat kidney is not demonstrated well. In the SHR, the ability of exogenous and endogenous renal dopamine to engender a natriuresis is impaired. Since renal dopamine levels in genetic models of hypertension are not lower than their normotensive controls, the impaired intrarenal paracrine effect of dopamine in these animal models of hypertension appears to be receptor or postreceptor mediated. And renal dopamine derives mainly from renal tubular dopamine production and to a lesser extent from dopaminergic nerves. The present study utilizes imrnunohistochemistry with specific antibodies to characterize the renal distribution of dopamine receptor subtypes and recognize the role of dopamine receptor defect in the pathogenesis of hypertension in 14-week-old WKY (mean HP 108+/-5mmHg) and SHR (mean RP 174+/-7 mmHg) kidneys. Also it utilizes antibody of tyrosine hyclroxylase (TH) to recognize the site of the dopamine production mediated by TH using light microscopic immunohistochemistry. In the immunohistochemistry of the WKY kidney, dopamine D1 receptor protein is localized to glomerulus, proximal tubule, distal tubule, renal vessels, cortical and medullary collecting duct. And in the SHR kidney, dopamine D1 receptor protein is localized to glomerulus, distal tubule, renal vessels, cortical and medullary collecting duct, and juxtaglomerular apparatus (JGA). But there is no demonstrable positive reaction in the proximal tubule and weakly positive reactions in the renal arterioles of SHR compared with WKY kidney. In the immunohisto-chemistry of the WKY kidney, dopamine D1 receptor protein is localized to glomerulus, proxirnal tubule, distal tubule, renal vessels, cortical and rnedullary collecting duct. And in the SHR kidney, dopamine D2 receptor protein is localized to glomerulus, distal tubule, renal vessels, cortical and medullary collecting duct, and JGA. So, there is no demonstrable positive reaction in the proximal tubule of SHR compared with WKY. In the glomerulus of the WKY and SHR kidneys, both dopamine D1 and D2 receptors are localized. In the in situ hybridization of the WKY and SHR kidneys, dopamine D and D receptors are only demonstrated at the renal vessels. The positive reaction to TH immunohistochemistry of the WKY and SHR kidneys is only observed in the renal medulla compared with negative reaction on the renal cortex. Considering the excretion of sodium up to 65-70% with volume expansion may be mediated by dopamine D1-like receptors in the proximal tubule, our immunohistochemistry findings for the dopamine receptors may support the failure of natriuretic response in the SHR due to an abnormal dopamine receptor. Also our results rnay mean that the glornerular filtration rate is mediated by both dopamine D1 and Dz receptors comparing with the previous studies that the glomerular filtration rate was mediated by dopamine D2 receptor. I'here are some differences in the receptors expressing sites on the previous radioligand binding and pharmacologic studies, but our results suggest that at least some of the renal dopamine DA and DAz receptors correspond structurally to the central dopamine D1 and D2 receptors. Finally the result of TH immunohisto-chemistry suggests that the production of dopamine in the proximal tubule is not mediated by TH.