Functional characterization of alpha-adrenoceptors on pancreatic islets of fa/fa Zucker rats.
Recently, a defect in pertussis toxin-independent actions of epinephrine on pancreatic B-cells of fa/fa Zucker rats was reported (Cawthorn and Chan (1991) Mol. Cell. Endocrinol. 75, 197-204). We now report studies of islet alpha 2-adrenoceptor function of fa/fa rats. Insulin and cAMP production by islets of obese rats were both inhibited by the alpha 2-adrenoceptor agonist clonidine. Calculated pD2 values for clonidine were 9.57 +/- 0.59 and 9.43 +/- 0.33 for lean and fa/fa rat islets, respectively. Yohimbine reversed clonidine effects equipotently in lean and obese rat islets (pA2 values of 7.48 +/- 0.57 vs 7.43 +/- 0.58). Unexpectedly, the alpha 1-antagonist prazosin stimulated insulin secretion from islets of obese but not lean rats. Functional characteristics of the alpha-adrenoceptors on fa/fa islets are thus similar to those recently designated alpha 2B. Altered expression of alpha-adrenoceptors on pancreatic islets of fa/fa rats may contribute to changes in the pertussis toxin-independent pathway of epinephrine action previously observed.
Chan
C B
CB
Department of Anatomy and Physiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Canada.
MacPhail
R M
RM
D000818:Animals; D002478:Cells, Cultured; D003000:Clonidine / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000502:physiology; D005260:Female; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000096:biosynthesis; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D009765:Obesity / Q000378:metabolism*; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011924:Rats, Zucker; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D015016:Yohimbine / Q000494:pharmacology
D007328:Insulin; D011942:Receptors, Adrenergic, alpha; D005576:Colforsin; D015016:Yohimbine; D000242:Cyclic AMP; D005947:Glucose; D003000:Clonidine; D011224:Prazosin; D004837:Epinephrine