Differential distribution of postjunctional alpha 2 adrenoceptors in human omental small arteries.
A pharmacologic characterization of the postjunctional alpha adrenoceptors of human omental small arteries was performed using a microvascular myograph. Both the alpha 1-selective agonist phenylephrine in the presence of yohimbine (0.3 microM, alpha 2-selective antagonist) and the alpha 2-selective agonist B-HT 933 in the presence of prazosin (0.3 microM, alpha 1-selective antagonist) evoked strong vasoconstriction. The responses to phenylephrine were competitively antagonized by prazosin, whereas the responses to B-HT 933 were competitively antagonized by yohimbine; the pA2-values were 9.24 and 8.34, respectively. An inverse relationship of the maximum response to B-HT 933 (r = -0.53; p less than 0.001), but not to phenylephrine or to norepinephrine (NE), against artery caliber was observed. The shifts of the NE concentration-response curves caused by yohimbine (0.1 microM) were more marked in the smaller rather than the larger vessels (r = -0.71; p less than 0.01), whereas the opposite was observed using 0.1 microM prazosin (r = 0.84; p less than 0.001). These data suggest that both alpha 1 and alpha 2 adrenoceptors are present in the human omental small arteries, but whereas postjunctional alpha 2 adrenoceptors appear to be located predominantly in the resistance arteries, postjunctional alpha 1 adrenoceptors appear to be distributed evenly along the arterial tree.
Nielsen
H
H
Institute of Pharmacology, University of Aarhus, Denmark.
Mortensen
F V
FV
Mulvany
M J
MJ
D000328:Adult; D000368:Aged; D001158:Arteries / Q000187:drug effects / Q000378:metabolism; D001381:Azepines / Q000494:pharmacology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D009852:Omentum / Q000098:blood supply; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism*; D012039:Regional Blood Flow / Q000187:drug effects; D014655:Vascular Resistance / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects; D015016:Yohimbine / Q000494:pharmacology
D001381:Azepines; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D015016:Yohimbine; C015603:azepexole; D009638:Norepinephrine; D011224:Prazosin