Characterization of Adrenoceptor Types and Subtypes in American Bullfrogs Acclimated to Warm or Cold Temperature

• Published in: General and comparative endocrinology 1996-11, Vol.104 (2), p.168-178
• Main Authors: Herman, Ceil A., Luczy, Georgia, Wikberg, Jarl E.S., Uhlén, Staffan
• Format: Article
• Language: English
• Subjects: Acclimatization; Adrenergic alpha-Antagonists - analysis; Adrenergic alpha-Antagonists - metabolism; Adrenergic beta-Antagonists - pharmacology; Animals; Binding, Competitive; Dose-Response Relationship, Drug; Humans; Idazoxan - analogs & derivatives; Idazoxan - analysis; Idazoxan - metabolism; Kidney - metabolism; Membrane Proteins - antagonists & inhibitors; Membrane Proteins - metabolism; Myocardium - metabolism; Pindolol - analogs & derivatives; Pindolol - analysis; Pindolol - metabolism; Prazosin - analysis; Prazosin - metabolism; Radioligand Assay; Rana catesbeiana - physiology; Receptors, Adrenergic - metabolism; Receptors, Adrenergic, alpha-1 - metabolism; Receptors, Adrenergic, alpha-2 - metabolism; Receptors, Adrenergic, beta - metabolism; Spinal Cord - metabolism; Temperature
• ISSN: 0016-6480; 1095-6840
• DOI: 10.1006/gcen.1996.0159

While indirect evidence suggested that the responsiveness of frog adrenoceptors changes in response to temperature, direct measurement of adrenoceptor binding following acclimation to warm and cold temperatures had not been done. In the present study, the radioligands [3H]prazosin, [3H]RX821002, and [125I]cyanopindolol were used to label and quantify α1-, α2-, and β-adrenoceptors in bullfrogs acclimated to warm or cold environments. The number of α1-, α2-, and β-adrenoceptors in atrium, ventricle, and kidney membranes was not significantly different between warm- and cold-acclimated frogs. Characterization of receptor subtypes using pharmacological antagonists demonstrated that α2-adrenoceptors in frog spinal cord and kidney were of the same pharmacological subtype, which is similar to the mammalian α2A-subtype. The β-adrenoceptor in frog ventricle, atrium, and kidney was the β2-subtype. These results suggest that while the α1-, α2-, and β-adrenoceptor types have evolved in the frog, multiple subtypes of adrenoceptors are not necessary for physiological regulation in this species.