Quantitative relationships between cyclic adenosine-3',5'-monophosphate and lipolysis in adipose tissue during the...

The objective was to study the control of lipolysis and to determine kinetic relationships between subcutaneous adipose tissue cyclic AMP concentrations and rates of lipolysis in primiparous dairy cows in late pregnancy and early lactation. Adipose tissue was biopsied from primiparous cows at -30, -15, -5, 5, 15, 30, and 60 d around parturition. Tissue was incubated with the following treatments: basal, no additions; isoproterenol at 10(-5) M; adenosine deaminase at 1 x 10(6) munits/ml; combined isoproteranol and adenosine deaminase; isoproteranol, adenosine deaminase, and 1 mM theophylline. Cyclic AMP was highest at .25 h and remained elevated for 2 h. Response of cyclic AMP at .25 h was 5-, 9-, 27-, and 38-fold for the four stimulatory treatments, respectively. Glycerol release at 2 h increased 3-, 2.3-, 2.7-, and 3-fold, respectively. Lipolysis was related logarithmically to cyclic AMP concentrations within and among treatments and times around parturition. Either logarithmic or Michaelis-Menten equations predicted similar maximum lipolysis but increased sensitivity to cyclic AMP in tissue from lactating compared with pregnant heifers. Thus, the sensitivity of response of lipolysis to cAMP may be increased in adipose tissue from first lactation cows. These relationships also may be useful in constructing and improving mechanistic models of adipose and whole animal metabolism.