AJP - Heart and Circulatory Physiology, Vol 253, Issue 2 365-H372, Copyright © 1987 by American Physiological Society
Effects of alpha-adrenergic blockade on coronary autoregulation in dogs
C. E. Jones, I. Y. Liang and P. A. Gwirtz
In alpha-chloralose-anesthetized, open-chest dogs, left coronary blood flow
and oxygen extraction were measured at perfusion pressures from 25 to 175
mmHg. Pressure-flow relationships were obtained before and after
alpha-blockade with prazosin or alpha 2-blockade with yohimbine in the
presence of beta-blockade with propranolol. The efficiency of flow
autoregulation with increments in pressure was calculated as the
closed-loop gain and as the slope of flow to pressure. In all animals the
highest gain and the lowest slope were seen when pressure increased from 75
to 125 mmHg. In the prazosin group before alpha-blockade the gain with this
pressure increase was 0.76 +/- 0.05, whereas in the yohimbine group before
alpha-blockade this gain was 0.75 +/- 0.03. Prazosin reduced the gain
within the pressure range of 75-125 mmHg by 41%, and this reduction was
statistically significant (P less than 0.05). Prazosin also significantly
increased the flow to pressure slope within this range. In addition, at all
pressures greater than or equal to 50 mmHg, the level of coronary flow was
significantly increased by prazosin. The increase in flow and the reduction
in autoregulatory efficiency with prazosin were not attributable to an
increase in myocardial oxygen consumption. Yohimbine had no effects on the
level of coronary flow or on the autoregulatory efficiency. These data
indicate that an alpha 1-adrenoceptor mediated coronary constriction
modulates coronary autoregulation.
