The Role of the Adrenals in the Regulation of Phosphoenolpyruvate Carboxykinase of Rat Adipose Tissue

Abstract

Abstract Fasting, as well as adrenalectomy, induced an increased rate of glyceride-glycerol synthesis from pyruvate in rat adipose tissue. When both treatments were combined, the elevation in the rate of glycerogenesis was more than additive. The activity of cytosol pyruvate carboxylase rose in tissues of adrenalectomized rats but not in those of fasted rats. P-enolpyruvate carboxykinase activity, on the other hand, was elevated by both treatments, and reached maximum values in adrenalectomized, fasted rats. The results suggest that the increase in glycerogenesis in fasted, adrenalectomized rats was due to increases in the activities of both pyruvate carboxylase and P-enolpyruvate carboxykinase. The effects of fasting and of adrenalectomy on P-enolpyruvate carboxykinase were both counteracted by corticosteroids and by actinomycin D. Corticosteroids were more effective than actinomycin, causing a faster decline and depressing enzyme activity to lower levels. This effect of corticosteroids on P-enolpyruvate carboxykinase was prevented by simultaneous administration of actinomycin. Liver P-enolpyruvate carboxykinase was not elevated by adrenalectomy, but liver from the fasted, adrenalectomized animals had a higher activity of this enzyme than did liver from the fasted rats. Contrary to the activity of the adipose tissue enzyme, the liver enzyme activity increased after short time intervals (2½ hours) following corticosteroid treatment.