Enzymes of adenosine metabolism of sheep adipose tissue: changes in activity with season, pregnancy and lactation.

Activities of enzymes involved in the synthesis and degradation of adenosine have been measured in samples of adipose tissue from unmated sheep at various times of the year between January and October and from pregnant and lactating sheep. 5'-Nucleotidase activity increased during the spring in unmated sheep but this increase was suppressed in lactating sheep. Neither adenosine kinase nor adenosine deaminase activities varied significantly between January and October in unmated sheep. Lactation resulted in a rise in adenosine deaminase activity and a small decrease in adenosine kinase activity. Pregnancy had no obvious effect on the activities of any of the three enzymes noted above. Changes in adipocyte mean cell volume and number per g tissue and the concentrations of DNA and protein of the tissue are also described. Results are discussed in relation to changes in the capacity for lipid synthesis and mobilization which occur in response to season, pregnancy and lactation in sheep.