title: Effects of temperature and plane of nutrition on beta-adrenergic receptors in heart, kidney, and liver of lambs.
abstract: We determined the effects of temperature and feed intake on beta-adrenergic receptors (beta-adrenoceptors) in tissues of sheep. Twenty-four lambs were exposed during three 5-wk periods to either thermoneutral, control (W; 23+/-2 degrees C) or cold (C; 0+/-2 degrees C) temperatures and were fed either ad libitum (A) or restricted (R) levels of feed intake, resulting in four treatment groups: WA, WR, CA, and CR. Hearts, kidneys, and livers were harvested at slaughter and binding of [3H]dihydroalprenolol to plasma membrane extracts was used to determine densities (B(MAX)) and binding affinities (Kd) of beta1 and beta2 adrenoceptors. The B(MAX) values ranged from 12.10 to 201.26 and 3.38 to 12.30 fmol/mg protein for beta1 and beta2 adrenoceptors, respectively; heart and kidney had the highest and lowest values, respectively. Feed restriction reduced (P < .05) beta1 and beta2 receptor densities in heart but increased (P < .05) beta1 receptor density in kidney and liver. Cold temperature exposure reduced beta1 receptor density in heart tissue during feed restriction. The Kd values, ranging from 1.32 to 5.98 nM, were increased (P < .05) by cold exposure and feed restriction in kidney and liver. Because the effectiveness of hormones is a function of their concentrations, binding affinities, and their receptor densities, these results imply that cold temperature exposure and feed restriction could potentially reduce (in heart) and increase (in kidney and liver) metabolic responsiveness of tissues to catecholamines.
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Canada.
authors.forename: E D
authors.initials: ED
authors.lastname: Ekpe
authors.forename: J A
authors.initials: JA
authors.lastname: Moibi
authors.forename: R J
authors.initials: RJ
authors.lastname: Christopherson
mesh_terms: D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002149:Energy Intake; D006706:Homeostasis; D007668:Kidney / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009929:Organ Size; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D012756:Sheep / Q000378:metabolism*; D013696:Temperature
chemical_list: D011943:Receptors, Adrenergic, beta