Adrenal contribution to coronary regulation in the newborn

Evidence for adrenergic regulation of the coronary vessels was sought in 27 newborn lambs. Sympathetic activity was altered by temporarily lowering cephalic perfusion pressure (CPP) from 90 to 20 mmHg while aortic pressure was held constant. Heart rate (HR) and left ventricular dP/dt max increased markedly, while end-diastolic pressure and stroke volume fell. These changes were accompanied by an increase in coronary blood flow (CBF), myocardial O2 consumption (MVO2), and reduced coronary resistance (CF) (P less than 0.005). After beta blockade, which prevented an augmentation of metabolic demand, the same maneuver resulted in coronary vasoconstriction, reflected by reduced CBF and increased CR (P less than 0.02). This response was eliminated by alpha blockade with phentolamine (2 mg/kg). In 13 lambs subjected to bilateral adrenalectomy or sham operation, lowering CPP elicited similar positive chronotropic and inotropic changes, increases of MVO2 and CBF, and reduced CR. Following beta blockade, lowering CPP in the sham group caused coronary constriction. However, no changes in CBF or CR were elicited in the adrenalectomized lambs. These observations indicate that integrity of the adrenal glands is required for adrenergic control of the coronary vessels in the newborn. Chronotropic and inotropic regulation is mediated by direct neural action and is not dependent on adrenal function.