title: Changes in postjunctional alpha-adrenoceptors during postnatal growth in rabbit arteries.
abstract: The pharmacological characteristics of the postjunctional alpha-adrenoceptors of vascular smooth muscle were studied in ring segments of thoracic aorta, superior mesenteric, and central ear arteries of 4- and 8-week-old, and young adult (12- to 16-week-old) rabbits. Norepinephrine (alpha 1, alpha 2-agonist), phenylephrine (alpha 1-agonist), and UK 14,304-18 (alpha 1-agonist) caused a concentration-dependent contraction of all three arterial segments from 4- and 8-week-old animals. Norepinephrine and phenylephrine but not UK 14,304-18 contracted the young adult thoracic aorta and superior mesenteric artery, whereas all the agonists contracted the central ear artery. The effects of the alpha 1-adrenoceptor antagonists, prazosin and thymoxamine, and the alpha 2-adrenoceptor antagonists, rauwolscine and yohimbine, on these responses were studied. In the 4-week-old rabbits, responses to norepinephrine, phenylephrine, and UK 14,304-18 were reduced by all four antagonists with nominal pA2 values in the range of 7-8.5. The action of the antagonists was competitive. Between 4 and 8 weeks, there was a significant decrease in the pA2 values of rauwolscine against norepinephrine and UK 14,304-18 in the aorta and between rauwolscine and UK 14,304-18 on the superior mesenteric artery. The pA2 values of rauwolscine and yohimbine, but not prazosin and thymoxamine, were lower in the young adult compared with values from the 8-week-old rabbit. In the interpretation of these results, there are two possibilities.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.forename: F M
authors.initials: FM
authors.lastname: Tayo
authors.forename: R D
authors.initials: RD
authors.lastname: Bevan
authors.forename: J A
authors.initials: JA
authors.lastname: Bevan
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000254:growth & development*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000294:innervation*; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha