title: Effect of maturation on alpha-adrenoceptor activity in newborn piglet mesentery.
abstract: To characterize the mesenteric alpha1- and alpha2-adrenoceptor populations in newborn piglets, an extracorporeal circuit was established to control intestinal blood flow in 0- to 2-day old and 10- to 14-day old animals. In both groups, alpha-adrenoceptor activation was first documented by observing dose-dependent increases in mesenteric perfusion pressure after intramesenteric arterial injection of alpha-adrenoceptor agonists. In the 10- to 14-day old piglets, mesenteric vasoconstrictor responses to alpha1-adrenoceptor agonists (methoxamine and norepinephrine) and an alpha2-adrenoceptor agonist (BHT-933) were each blunted (P < 0.05, analysis of variance) by peripheral intravenous injections of prazosin (an alpha1-adrenoceptor antagonist) and yohimbine (an alpha2-adrenoceptor antagonist), respectively. The mesenteric vasoconstrictor responses to those agonists were not significantly attenuated by prazosin or yohimbine in 0- to 2-day old animals, nor were they blunted by YM-12617 (alpha1-adrenoceptor antagonist) or idazoxan (alpha2-adrenoceptor antagonist)--compounds that are structurally unrelated to prazosin and yohimbine, respectively. In addition, mesenteric vasoconstrictor responses to other known vasoconstrictor agents--angiotensin II, neuropeptide Y, and a thromboxane A2 mimic (U-46619)--were not effected in either age group by prazosin or yohimbine, implying these agents act independently of alpha-adrenoceptor mechanisms. These data suggest that (1) there exists functional mesenteric alpha1- and alpha2-adrenoceptor-like activity in 10- to 14-day old piglets that, in 0- to 2-day old animals, is not specifically expressed; and (2) mesenteric alpha-adrenoceptor function becomes more selective as newborn piglets mature.
authors.affiliation: Department of Surgery, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA.
authors.forename: T V
authors.initials: TV
authors.lastname: Hoang
authors.forename: E U
authors.initials: EU
authors.lastname: Choe
authors.forename: H L
authors.initials: HL
authors.lastname: Lippton
authors.forename: A L
authors.initials: AL
authors.lastname: Hyman
authors.forename: L M
authors.initials: LM
authors.lastname: Flint
authors.forename: J J
authors.initials: JJ
authors.lastname: Ferrara
mesh_terms: D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D005260:Female; D008297:Male; D008638:Mesenteric Arteries / Q000502:physiology*; D011224:Prazosin / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D013552:Swine; D014661:Vasoconstriction / Q000187:drug effects; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D011224:Prazosin