Alpha 2-receptors mediate catecholamine-stimulated acid secretion in Amphiuma jejunum.
The receptors mediating adrenergic stimulation of acid secretion by Amphiuma jejunum were characterized in this study using alpha- and beta-adrenergic agonists and antagonists. Isolated segments of jejunum were mounted in Ussing chambers and bathed in Cl- -free (SO4(2-] medium. Shortcircuit current (Isc) and acid secretion (JH) were recorded, the latter by measuring the rate of alkalinization of the serosal medium. The beta-adrenergic receptor antagonist, propranolol (10(-4) M), had no effect on the Isc and JH stimulated by norepinephrine (NE). The alpha 2-adrenergic agonists, clonidine and UK-14,304, mimicked the effect of NE, with effective concentrations providing 50% maximal delta Isc of 2.0 X 10(-7) and 9.0 X 10(-8) M, respectively. NE added subsequently produced no greater stimulation. In contrast, the alpha 1-adrenergic agonists, phenylephrine and methoxamine, produced little stimulation of JH and Isc; NE added subsequently stimulated the Isc. The alpha 1-adrenergic antagonist prazosin had no effect on the NE-induced Isc or JH, whereas the alpha 2-adrenergic antagonist yohimbine inhibited the NE-stimulated Isc with a half-maximal effective concentration of 3.5 X 10(-7) M. Yohimbine (10(-4) M) reduced the NE-stimulated Isc by 88%, whereas the spontaneous Isc was reduced by only 12%. These results demonstrate that alpha 2-adrenergic receptors on the basolateral membrane of Amphiuma enterocytes mediate NE-enhanced, but not spontaneous, intestinal acid secretion.
Hinton
C F
CF
Department of Physiology, Emory University, Atlanta, Georgia 30322.
White
J F
JF
D000818:Animals; D000068438:Brimonidine Tartrate; D003000:Clonidine / Q000494:pharmacology; D066298:In Vitro Techniques; D007583:Jejunum / Q000187:drug effects* / Q000378:metabolism; D008729:Methoxamine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D010656:Phenylephrine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011522:Protons; D011810:Quinoxalines / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D013268:Stimulation, Chemical; D014562:Caudata
D011522:Protons; D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D000068438:Brimonidine Tartrate; D011433:Propranolol; D008729:Methoxamine; D003000:Clonidine; D009638:Norepinephrine