Adenosine and the control of lipolysis in rat adipocytes during pregnancy and lactation

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Abstract
The rate of noradrenaline[norepinephrine, NE]-stimulated lipolysis is lower in fat-cells from lactating than from pregnant rats; this difference is eliminated by the addition of adenosine deaminase. The activity of 5''-nucleotidase, and hence the capacity of the cells to synthesize adenosine, was the same in fat cells and also stromal cells of adipose tissue from pregnant, lactating and male rats. The response and sensitivity of fat cells to the anti-lipolytic effects of adenosine were measured by incubating cells in the presence of NE, adenosine deaminase (to remove endogenous adenosine) and various concentrations of the adenosine analog N6-phenylisopropyladenosine (PIA). PIA caused a greater inhibition of the rate of NE-stimulated lipolysis in adipocytes from lactating than from pregnant rats. The concentration of PIA required to inhibit by 50% the rate of NE-stimulated lipolysis fell from over 100 nM for fat cells from pregnant rats to 30 nM for fat cells from lactating rats. The decreased rate of NE-stimulated lipolysis during lactation was not due to the smaller mean cell volume of adipocytes during this state.