Effects of temperature and plane of nutrition on beta-adrenergic receptors in heart, kidney, and liver of lambs

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 [H-3]dihydroalprenolol to plasma membrane extracts was used to determine densities (B-MAX) and binding affinities (K-d) of beta 1 and beta 2 adrenoceptors. The B-MAX values ranged from 12.10 to 201.26 and 3.38 to 12.30 fmol/mg protein for beta 1 and beta 2 adrenoceptors, respectively; heart and kidney had the highest and lowest values, respectively. Feed restriction reduced (P < .05) beta 1 and beta 2 receptor densities in heart but increased (P < .05) pi receptor density in kidney and Liver. Cold temperature exposure reduced pi 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.