Background: It has been shown recently that the pregnancy and parturition hormone, relaxin, is secreted by the heart. This study examined the effects of relaxin in small human resistance arteries from the systemic and pulmonary circulations.
Methods and results: Arteries were obtained from gluteal biopsies and resected lung tissue and studied with the use of wire myography. Cumulative concentration relaxation curves were constructed in systemic arteries with substance P, epoprostenol, atrial natriuretic peptide, and relaxin (concentration range 10(-13) -10(-7)M). The maximal responses were 88(+/-5)%, 67(+/-10)%, 52(+/-16)% and 66(+/-16)%, respectively. Endothelium removal virtually abolished the action of relaxin. Relaxin had no vasodilator effect in pulmonary arteries.
Conclusions: Relaxin is a powerful dilator of systemic resistance arteries secreted by the heart that may contribute to cardiovascular regulation.