CHARACTERIZATION OF ADRENOCEPTOR TYPES AND SUBTYPES IN AMERICAN BULLFROGS ACCLIMATED TO WARM OR COLD TEMPERATURE

While indirect evidence suggested that the responsiveness of frog adre noceptors changes in response to temperature, direct measurement of ad renoceptor binding following acclimation to warm and cold temperatures had not been done. In the present study, the radioligands [H-3]prazos in, [H-3]RX821002, and [I-125]cyanopindolol were used to label and qua ntify alpha(1)-, alpha(2)-, and beta-adrenoceptors in bullfrogs acclim ated to warm or cold environments. The number of alpha(1)-, alpha(2)-, and beta-adrenoceptors in atrium, ventricle, and kidney membranes was not significantly different between warm- and cold-acclimated frogs. Characterization of receptor subtypes using pharmacological antagonist s demonstrated that alpha(2)-adrenoceptors in frog spinal cord and kid ney were of the same pharmacological subtype, which is similar to the mammalian alpha(2A)-subtype. The beta-adrenoceptor in frog ventricle, atrium, and kidney was the beta(2)-subtype. These results suggest that while the alpha(1)-, alpha(2)-, and beta-adrenoceptor types have evol ved in the frog, multiple subtypes of adrenoceptors are not necessary for physiological regulation in this species. (C) 1996 Academic Press, Inc.