ABSTRACT
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.