A role for the thromboxane receptor in L-NAME hypertension

Actions of the lipid mediator thromboxane (Tx) A(2) acting through the TP receptor contribute to the pathogenesis of cardiovascular disease. To further explore the role of TxA(2) in hypertension, we examined the consequences of deficiency of the TP receptor on the course of hypertension associated with endothelial dysfunction and salt sensitivity. To this end, the nitric oxide synthase inhibitor N-G-nitro-L-arginine methyl ester (L-NAME) was administered to TP-deficient (Tp(-/-)) and wild-type (Tp(+/+)) control mice in drinking water for 21 wk along with a high- salt (HS; 6% NaCl) diet. Administration of L- NAME increased urinary excretion of TxB(2) to a similar extent in both Tp(+/+) and Tp(-/-) animals. L-NAME also caused significant and sustained elevations in blood pressure that reached a maximum between weeks 3 and 6. However, the severity of hypertension was attenuated in the Tp(-/-) mice throughout the study period (P<0.001). At the end of the study, the wild- type mice developed significant cardiac hypertrophy (23.6 +/- 2% increase in heart-to-body weight ratio). The severity of cardiac hypertrophy was attenuated in the TP-deficient group (11.1 +/- 2.6%; P < 0.05). In contrast, kidney hypertrophy was exaggerated in the Tp(-/-) mice compared with controls (37.1 +/- 5.4 vs. 12.3 +/- 2.3%; P < 0.01). Moreover, the severity of glomerulosclerosis, tubule vacuolization, and interstitial chronic inflammation was also enhanced in the Tp(-/-) group (P < 0.01). Thus, in L- NAME hypertension, TP receptors contribute to elevated blood pressure and cardiac hypertrophy. In this model, TP receptors also provided unexpected protection against kidney injury.