AJP - Heart and Circulatory Physiology, Vol 234, Issue 2 173-H179, Copyright © 1978 by American Physiological Society
Adrenal contribution to coronary regulation in the newborn
S. E. Downing, W. E. Hellenbrand, J. C. Lee and D. B. Nudel
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.
