AJP - Heart and Circulatory Physiology, Vol 247, Issue 6 928-H935, Copyright © 1984 by American Physiological Society
Regional differences in alpha 1-adrenoceptor numbers and responses in canine aorta
K. K. Griendling, A. Sastre and W. R. Milnor
The relationship between active force and alpha 1-adrenergic receptor
binding in vascular smooth muscle was measured on strips of canine aorta.
After measurement of the isometric force produced by l-phenylephrine and
l-norepinephrine in vitro, [3H]prazosin was used to determine the affinity
and numbers of alpha 1-receptors in homogenates prepared from the strips.
Maximum active stress was 440 g/cm2 in the ascending, 317 in the descending
thoracic, and 252 in the abdominal aorta. The total number of alpha
1-receptors per gram arterial wall averaged 576, 237, and 136 fmol/g,
respectively. Affinity of the receptors was the same in all regions for
prazosin (87 pM) and l-phenylephrine (9 microM). The relation between
number of agonist-occupied receptors and response was similar in all
regions but nonlinear; 50% of the maximum stress developed when only 2-11%
of the receptors were occupied. Differences of contractile response within
the vascular tree may thus arise from regional differences in the number of
appropriate receptors present, rather than differences of affinity or
occupation-response relationships.
