Effects of blood and crystalloid cardioplegia on adrenergic and myogenic vascular mechanisms.

BACKGROUND: This study compares the effects of cold blood and crystalloid cardioplegia on adrenergic and myogenic regulation of the coronary circulation.
METHODS: Pigs were placed on cardiopulmonary bypass and hearts were arrested with a hyperkalemic crystalloid cardioplegic solution (Cryst CP) or blood cardioplegic solution (Blood CP) for 1 hour. Hearts of selected pigs were then reperfused for 1 hour (Rep) and separated from cardiopulmonary bypass. Left ventricular perfusion and contractility and beta- and alpha 2-adrenergic and myogenic responses of the coronary circulation were examined.
RESULTS: Relaxation of isolated, precontracted microvessels to isoproterenol (beta-adrenoceptor agonist) was reduced to a lesser extent after Blood CP as compared with Cryst CP. Relaxation to forskolin (adenylate cyclase activator) was reduced after Cryst CP, but was preserved after Blood CP. After 1 hour of postcardioplegia reperfusion, the respective responses to isoproterenol and forskolin were similar in vessels from the Cryst CP-Rep and Blood CP-Rep groups. The alpha 2-adrenoceptor-mediated, endothelium-dependent vascular relaxation to clonidine was decreased more after Cryst CP than after Blood CP. The relaxation to nitroprusside was not affected by either Cryst CP or Blood CP. Myogenic tone was decreased to a lesser extent after Blood CP versus Cryst CP. Baseline coronary blood flow, isoproterenol-induced increases of coronary blood flow, and indices of myocardial contractility were similar in the Blood CP-Rep and Cryst CP-Rep groups, both 5 and 60 minutes after initiation of reperfusion.
CONCLUSIONS: Although Blood CP was superior to Cryst CP in preserving beta- and alpha 2-adrenoceptor function and myogenic tone in vitro, there was no demonstrable benefit of blood cardioplegia in the preservation of myocardial contractility or perfusion in this model of cardioplegia.