Transcardiac and transpulmonary gradients in the putative new cardiovascular hormone relaxin.

Relaxin, a polypeptide hormone belonging to the insulin family, has recently attracted interest as a possible cardiovascular regulator. Though long known to prepare the birth canal for parturition, relaxin has only lately been shown to have renal and haemodynamic actions. Relaxin may also be secreted by the heart, at least when it is failing. Plasma relaxin concentrations are raised in chronic heart failure (CHF) and myocardial expression of the H1 and H2 relaxin gene is increased in proportion to the severity of CHF. Whether the heart is a source of relaxin when cardiac contractility is preserved is unknown. The lungs are commonly involved in the clearance or secretion of vasoactive peptides but their role in relaxin metabolism is unknown. The aim of this study was to measure transcardiac and transpulmonary relaxin gradients in subjects with preserved left ventricular ejection fraction. Patients undergoing coronary artery bypass grafting were studied as both pulmonary and cardiac arterial inflow and venous effluent can be readily sampled.