Enhanced coronary arteriolar contraction to vasopressin in patients with diabetes after cardiac surgery.

OBJECTIVE: Cardioplegic arrest (CP) and cardiopulmonary bypass (CPB) are associated with vasomotor dysfunction of coronary arterioles in patients with diabetes (DM) undergoing cardiac surgery. We hypothesized that DM may up-regulate vasopressin receptor expression and alter the contractile response of coronary arterioles to vasopressin in the setting of CP/CPB.

METHODS: Right atrial tissue samples of patients with DM and without (ND) (n = 8 in each group) undergoing cardiac surgery were harvested before and after CP/CPB. The isolated coronary arterioles (80-150 μm) dissected from the harvested right atrial tissue samples were cannulated and pressurized (40 mm Hg) in a no-flow state. The changes in diameter were measured with video microscopy. The protein expression/localization of vasopressin 1A receptors (V1A) and vasopressin 1B receptors (V1B) in the atrial tissue were measured by immune-blotting and immunohistochemistry.

RESULTS: The pre-CP/CPB contractile responses of the coronary arterioles to vasopressin were significantly increased post-CP/CPB in both the ND and DM groups. This effect was more pronounced in the vessels from patients in the DM group than that of vessels from patients in the ND group (P < .05). Vasopressin-induced contractile response of the coronary arterioles was inhibited in the presence of the specific V1A antagonist SR 49059 (10-7  M) in both ND and DM vessels (P < .05). The post-CP/CPB protein levels of V1A were significantly increased compared with pre-CP/CPB values in both the ND and DM groups (P < .05), whereas this increase was greater in DM than that of ND (P < .05). Immunohistochemistry staining further indicates that V1B were mainly expressed in the myocardium but not in vascular smooth muscle.

CONCLUSIONS: CP/CPB and DM are both associated with up-regulation in V1 receptor expression/localization in human myocardium. Vasopressin may induce coronary arteriolar constriction via V1A. This alteration may lead to increased coronary arteriolar spasm in patients with DM undergoing CP/CPB and cardiac surgery.