Relaxin ameliorates salt-sensitive hypertension and renal fibrosis.

Background: Although relaxin (RLX) has potent vasodilatory and anti-fibrotic properties, there is no information on its effects on salt-sensitive hypertension.

Methods: We investigated the effects of short-term treatment with RLX on blood pressure (BP) and nitric oxide synthase (NOS) protein in the kidneys of male Dahl salt-sensitive (DS) and Dahl salt-resistant (DR) rats after 1 week consumption of an 8% NaCl diet. We also evaluated the inhibitory effects of each specific NOS inhibitor on BP during 1-week RLX treatment under high-salt diet. Next, we examined the long-term effects of RLX treatment for 6 weeks on renal histology and transforming growth factor-beta1 (TGF-β1) expression in male DS and DR rats placed on the 8-week high-salt diet.

Results: The short-term RLX treatment significantly attenuated the high-salt diet-induced rise in BP in DS rats with increasing neuronal NOS and endothelial NOS protein in kidneys. Selective inhibition of each of the three NOS isoforms significantly blocked the anti-hypertensive effects of RLX in DS rats after 1-week high-salt diet. The long-term treatment of DS rats with RLX for 6 weeks significantly reduced systolic BP, lessened glomerular and tubulointerstitial changes and reduced TGF-β signaling compared to saline-treated controls.

Conclusions: The results suggested that RLX converted salt sensitivity to salt resistance, at least in part, by up-regulating NOS. RLX is a potentially useful therapeutic agent for salt-sensitive hypertension.