Desensitisation of β‐Adrenergic Responsiveness in vivo

Chronic catecholamine stimulation in vivo of brown adipose tissue during acclimation of hamsters to cold does not result in any alteration of p‐adrenergic receptor number or affinity when determined in isolated adipocytes by (–)‐[ 3 H]dihydroalprenolol binding. Norepinephrine displacement of (–)‐[ 3 H]dihydroalprenolol showed the same K i for both groups. However, the slope of the displacement curve was shallower for cells from cold‐acclimated animals than for controls. Cyclic AMP accumulation was stimulated by norepinephrine in cells from both groups of animals, although the dose‐response curve for cells from cold‐acclimated animals was shifted to the right and the maximum value obtained was less than half that found in cells from control animals. The slope of the curve was again lower. Other catecholamines stimulated CAMP accumulation with an order of potency in agreement with a response mediated through β 1 ‐adrenergic receptors. The dose‐response curve for norepinephrine‐stimulated oxygen consumption was also shifted to the right for cells from cold‐acclimated animals, although the maximal respiration was only slightly reduced. The slope factor was again decreased. The results are interpreted in terms of a reduced coupling between the β‐receptor and the metabolic response in isolated brown adipocytes from cold‐acclimated animals as a result of chronic catecholamine stimulation in vivo.