Abstract
COX-2 is an inducible cyclooxygenase (COX) that has been reported to be expressed in the macula densa and surrounding cortical thick ascending limb in normotensive rats. The present study assessed the contribution of COX-2 in three different rat models of hypertension, each characterized by a different activation of the renal renin-angiotensin system. Mean blood pressure (MBP) in the rat 2 kidney-1 clip (2K1C) model was significantly reduced with a COX-2 selective inhibitor, NS-398 (10 mg/kg, p.o., twice a day) (vehicle-administered rats (n =8): 154±6 mmHg; NS-398-administered rats (n =5): 128±10 mmHg). By contrast, a COX-1 selective inhibitor, mofezolac, did not lower MBP. Increased plasma renin activity (23±8 ng/kg/h (n =6) vs. sham operation, 2.4±0.9 ng/kg/h (n =4)) was markedly reduced to 6.8±2.7 ng/ml/h (n =5) by NS-398, but not by mofezolac. The development of 1 kidney-1 clip (1K1C) hypertension was also inhibited by NS-398 (vehicle (n =12): 133±1 mmHg; NS-398 (n =7): 122±3 mmHg) accompanied by a reduction in plasma renin activity (3.0±0.3 ng/ml/h, n =4) to 1.0±0.2 ng/ml/h (n =5). The COX-2 inhibitor increased urinary excretions in the 1K1C model, but not in the 2K1C model. In a deoxycorticosterone acetate (DOCA)-salt model, plasma renin activity was markedly suppressed to less than 0.3 ng/ml/h. The COX-2 inhibitor caused no significant changes in MBP, plasma renin activity, or urinary excretion, suggesting that COX-2 made a lesser contribution in this model. Increased expression of COX-2 mRNA and protein was observed in the kidneys of 1K1C and 2K1C rats, but not in DOCA-salt rats. These results suggest that COX-2 plays a significant role in the development of 2K1C and 1K1C renovascular hypertension, in addition to making a substantial contribution to the diuretic effect in the 1 K1C model. (Hypertens Res 2002; 25: 927-938)
