The divergence in the excitation-contraction coupling of rat mesenteric resistance arteries lies distal to the receptor site.
In vitro studies were performed with rat mesenteric resistance arteries (diameter 158-271 microns) mounted as ring preparations in an isometric myograph. Noradrenaline evoked concentration-dependent, tonic contractions in calcium-containing media, whereas transient responses were elicited by the agonist in a concentration-dependent manner in calcium-free media; the pD2 values (-log EC50) were 6.73 and 5.71, respectively. The responses to noradrenaline in calcium-containing media were competitively inhibited by the alpha 1-selective antagonist, prazosin (pA2:9.23), and the responses to noradrenaline in calcium-free media were abolished by 10 nM prazosin. The agonist affinities expressed as the pKD values (-log KD) for the receptor mediating the response to noradrenaline in calcium-containing and calcium-free media were 5.78 and 5.64, respectively. These data suggest that although much higher concentrations of noradrenaline are required to elicit responses in calcium-free media than in calcium-containing media, both types of response are mediated by one adrenoceptor subtype, the alpha 1-adrenoceptor.
Nielsen
H
H
Department of Pharmacology, University of Aarhus, Denmark.
Mulvany
M J
MJ
D000818:Animals; D002118:Calcium / Q000378:metabolism; D003470:Culture Media; D004305:Dose-Response Relationship, Drug; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects* / Q000378:metabolism; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011921:Rats, Inbred WKY; D011941:Receptors, Adrenergic / Q000187:drug effects / Q000378:metabolism*; D014655:Vascular Resistance / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects*
D003470:Culture Media; D011941:Receptors, Adrenergic; D002118:Calcium; D009638:Norepinephrine; D011224:Prazosin