Effects of adrenocorticotropin and cycloheximide on adrenal diglyceride kinase

We studied the effects of adrenocorticotropin (ACTH) and cycloheximide on adrenal enzymes involved in phosphatidate synthesis. Treatment of rats in vivo with ACTH induced a rapid increase in phosphatide synthesis from diglyceride and ATP in adrenal homogenates, and cycloheximide treatment prevented this increase if given before ACTH and rapidly reversed the increase if given after ACTH. The stimulatory effect of ACTH appeared to be largely due to an increase in diglyceride substrate, as kinase activity was not altered. The inhibitory effect of cycloheximide, on the other hand, appeared to be due to a decrease in diglyceride kinase activity. Neither ACTH nor cycloheximide treatment had any effect on the activity of glycerol-3'-phosphate acyltransferase or phosphatidate phosphatase. Our findings suggest that (a) ACTH increases the flow of phospholipid (and their levels) throughout the entire circular pathway, i.e., phosphatidate leads to CDP-diacylglycerol leads to inositides leads to diglycerides leads to phosphatidate, and (b) a labile protein may serve to allow entry into a recycling of diglyceride in this pathway. In addition, since cycloheximide blocked carbachol-induced increases in pancreatic and salivary glandular phosphatidate synthesis resulting from phosphatidylinositol hydrolysis and consequent diglyceride generation, the putative labile protein may have widespread importance.