Differential effect of hypothermia on the vascular tone and reactivity of the human coronary artery and graft vessels

Hypothermia may contribute to vascular spasm during bypass surgery. The effect of cooling on the reactivity of the human coronary artery (CA), saphenous vein (SV) and internal mammary artery (IMA) was studied in vitro. In CA and IMA cooling diminished the resting tension and the contraction to potassium, noradrenaline and 5-hydroxytryptamine. In contrast, in SV the contraction to noradrenaline and 5-hydroxytryptamine was augmented by cooling. The effect of cold was reversible. These results demonstrate different effects of hypothermia in CA and the graft vessels. Thus, hypothermia augments the receptor-mediated contraction in SV but depresses it in IMA which thereby resembles CA. The difference is most marked in the contractile response to 5-hydroxytryptamine, which may accumulate during surgery. This may contribute to spasm in the saphenous vein grafts and may be involved in the mechanisms responsible for the inferior patency of SV compared to IMA as a graft vessel.