Alpha 2-adrenergic receptor-mediated regulation of intestinal calcium transport.
The role of alpha 2-adrenergic receptors in the regulation of intestinal Ca2+ transport was studied in vitro in rabbit proximal colon and distal ileum. Unidirectional mucosal-to-serosal and serosal-to-mucosal fluxes (Jm----s and Js----m) of 45Ca2+ were measured across isolated mucosal sheets bathed on both sides with identical Ringer solutions (1.25 mM Ca2+) and short-circuited. In the proximal colon, mucosal-to-epithelial influx (Jm----e) of Ca2+ was also determined. Proximal colonic mucosa secreted Ca2+ (in nmol X h-1 X cm-2, Jm----s = 12.1 and Js----m = 42.2). Epinephrine (10 microM) abolished Ca2+ secretion (Jm----s = 24.1 and Js----m = 24.9) but did not affect Jm----e (21.4 in controls and 23.6 after epinephrine). These effects were mediated by alpha 2-adrenergic receptors: yohimbine abolished the effect of epinephrine, but prazosin and propranolol did not; furthermore, clonidine mimicked the effects of epinephrine, whereas methoxamine and isoproterenol had no effect. Ileal mucosa did not transport Ca2+ spontaneously; epinephrine (10 microM) increased Jm----s in the ileum without affecting Js----m, thereby stimulating net Ca2+ absorption. The mechanism for these alpha 2-receptor-mediated effects was examined in proximal colon. The effect of epinephrine on Jm----s was dependent on serosal Na+ but was unaffected by ouabain or the Na+-Ca2+ exchange inhibitor, benzamil. The effect of epinephrine on Js----m was dependent on serosal Na+ and was blocked by both ouabain and benzamil. In the absence of epinephrine benzamil did not alter Jm----s or Js----m.(ABSTRACT TRUNCATED AT 250 WORDS)
Hyun
C S
CS
Cragoe
E J
EJ
Field
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M
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D003106:Colon / Q000378:metabolism; D004837:Epinephrine / Q000494:pharmacology; D007082:Ileum / Q000378:metabolism; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000187:drug effects; D008297:Male; D008954:Models, Biological; D010042:Ouabain / Q000494:pharmacology; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D012964:Sodium / Q000502:physiology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; C013407:benzamil; D010042:Ouabain; D000584:Amiloride; D012964:Sodium; D002118:Calcium; D004837:Epinephrine