The effect of alpha2-adrenergic receptors on cutaneous water evaporation in the rock pigeon (Columba livia).
The role of beta-adrenergic receptors in regulating cutaneous water evaporation (CWE) in the rock pigeon (Columba livia) is well documented. Here, we studied the involvement of the alpha2-adrenergic receptors in this cooling mechanism of the heat-acclimated (HAc) pigeon. Systemic alpha2-adrenergic activation [clonidine, 50 microg kg(-1), intramuscular (i.m.)] was found to increase CWE in heat-acclimated pigeons at an ambient temperature (T(a)) of 25 degrees C. Subcutaneous administration of the drug had no significant effect. Preinjection of an alpha2-adrenergic antagonist (yohimbine, 10 mg kg(-1), i.m.) completely prevented clonidine-induced CWE and attenuated propranolol-induced CWE by 53%. Pretreatment with a beta-adrenergic agonist (isoproterenol, 4 mg kg(-1), i.m.) abolished the effect of clonidine. None of the above treatments was found to elicit significant CWE in nonacclimated (NAc) pigeons. These findings, in addition to previously reported data, indicate a complex regulatory pathway of CWE in the heat-acclimated pigeon consisting of alpha2- and beta2-adrenergic receptors. The possible hierarchical pattern of these receptors is discussed.
Ophir
Eshel
E
Department of Cell and Animal Biology, Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel. eshel@vms.huji.ac.il
Arieli
Yehuda
Y
Marder
Jacob
J
D058669:Adrenergic alpha-2 Receptor Antagonists; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D010856:Columbidae / Q000502:physiology*; D003890:Desiccation; D007545:Isoproterenol / Q000494:pharmacology; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D012867:Skin / Q000187:drug effects / Q000378:metabolism*; D013696:Temperature; D014867:Water / Q000032:analysis* / Q000737:chemistry; D015016:Yohimbine / Q000494:pharmacology
D058669:Adrenergic alpha-2 Receptor Antagonists; D018341:Receptors, Adrenergic, alpha-2; D014867:Water; D015016:Yohimbine; D007545:Isoproterenol; D003000:Clonidine