An in vitro model was used to investigate effects of beta-hydroxybutyrate and isoproterenol (beta-adrenergic receptor agonist) on lipolysis in isolated adipocytes from late pregnant and recently calved dairy cows (n = 5) and cows with clinical ketosis (n =3). Incubation with 3.0 mmol/L beta-hydroxybutyrate reduced lipolysis in isolated adipocytes. This inhibitory effect was lower in the first lactation week (47% +/- 16%) compared with late pregnancy (71% +/- 6.5%). Incubation with 0.3 mu mol/L isoproterenol stimulated lipolysis in isolated adipocytes from periparturient dairy cows. Basal lipolysis resulted in non-esterified fatty acid to glycerol ratios in the incubation media of 2.0 +/- 0.23 in prepartum samples, 2.1 +/- 0.23 in the first lactation week and 2.2 +/- 0.09 in cows with clinical ketosis. beta-Hydroxybutyrate reduced lipolysis by 45% +/- 9.6% in isolated adipocytes from cows with clinical ketosis, indicating that impaired feedback of beta-hydroxybutyrate may not play a role in the disease etiology. (C) 2012 Elsevier Ltd. All rights reserved.