Beta-adrenergic receptor involvement in lipolysis of dairy cattle subcutaneous adipose tissue during dry and...

The influence of lactation on beta-adrenergic receptor kinetics was studied with adipocytes from eight Holstein cows during two physiological states, dry period 30 days prepartum and 30 days postpartum or early lactation. Physiological state had no effect on binding kinetics of (--)-hydrogen-3 labeled dihydroalprenolol. Affinity rate constants (8.2 versus 7.2 X 10(7) min-1 M-1) and equilibrium dissociation constants (7.1 versus 7.9 nM) for both prepartum and postpartum periods were similar. In contrast, the apparent number of beta-adrenergic receptors varied with lactational state (42,154 versus 72,264 sites/cell) for dry and lactating status as estimated in assays containing 5 nM (--)-hydrogen-3 dihydroalprenolol. Glycerol release and adipocyte concentrations of adenosine-3',5'-cyclic phosphoric acid were assayed with or without 10 microM epinephrine. Epinephrine elicited greater release of glycerol in adipocytes from lactating than dry cows (3.91 versus 2.1 mumol/10(6) cells/120 min). The concentration of adenosine-3',5'-cyclic phosphoric acid rose during the first 5 min of incubation in the presence of epinephrine and then fell to base after 10 min. Maximum concentrations at 5 min were not different in adipocytes from dry and lactating cows (250 versus 280 pmol/10(6) cells).