Relaxin in Vascular Physiology and Pathophysiology: Possible Implications in Ischemic Brain Disease

The hormone relaxin, known for its action on the female reproductive tract, is also able to act on organs and systems different from the reproductive ones, including the blood vessels, the heart and the brain. Relaxin causes vasodilation in several organs stimulating the biosynthetic pathway of nitric oxide (NO), a potent vasodilator. Relaxin also has a cardioprotective action: it reduces the inflammatory activation of neutrophils and their adhesion to the endothelium, and protects against myocardial injury caused by ischemia and reperfusion (I-R) in experimental animal models of myocardial infarction. Its mechanisms of action chiefly depend on the hormone's vasodilatory and anti-inflammatory properties. Recently, an additional form of relaxin has been discovered in the brain, where it has been postulated to act locally as a neurotransmitter. Relaxin, acting mainly on circumventricular organs, stimulates water drinking and vasopressin release and appears to be involved in the regulation of behavioural processes. Based on its properties on the cardiovascular system, it is possible to hypothesise that relaxin could regulate the vascular tone in the central nervous system and, going a step further, could protect the brain from IR-induced damage, possibly by an NO-mediated mechanism. This latter possibility is supported by the observation that relaxin is able to up regulate the endogenous production of NO in several target cells, as NO, at appropriate levels, is known to be involved in the protection against neural pathophysiological processes such as I-R-induced injury.