In vitro Responses to Atrial Natriuretic Polypeptide in Human Vessels Commonly Used as Aortocoronary Bypass Grafts

Vascular effects of atrial natriuretic polypeptide (APII), i.e. the peptide hormone released from the atrial myocardium, were investigated in segments of the human internal thoracic artery (ITA) and saphenous vein (SV) with intact (+E) or injured (-E) endothelium. All segments were subject to several cycles of agonists in order to detect tachyphylactic or facilitatory responses. Opposite, indirect effects on the noradrenaline contracted ITA and SV were obtained in response to APII at a supranormal concentration (50 nM) which had no direct relaxing action on the isolated segments in vitro. In ITA the noradrenaline contractures in subsequent cycles were reduced to 41 +/- 21% (+E) and 28 +/- 9% (-E), but in SV they were enhanced to 211 +/- 115% (+E) and 483 +/- 242% (-E) of those before APII exposure. Thus under in vitro conditions ITA could be indirectly relaxed by APII via tachyphylactic effect on the noradrenaline contracture. SV, on the other hand, was markedly potentiated by APII in its noradrenaline response. In injured endothelium these opposite effects were aggravated.