Molecular Pharmacology, Vol 5, 382-393, Copyright © 1969 by the American Society for Pharmacology and Experimental Therapeutics

Phospholipid Metabolism and Adrenal Medullary Activity

I. The Effect of Acetylcholine on Tissue Uptake and Incorporation of Orthophosphate-³²P into Nucleotides and Phospholipids of Bovine Adrenal Medulla

¹ Department of Pharmacology and Therapeutics, McGill University, Montreal, Canada

Bovine adrenal medullary slices were incubated at 30° in Locke’s solution containing orthophosphate-³²P or glycerol-1-¹⁴C. ³²P was incorporated into all individual phospholipids, but at different rates. The highest specific activity observed was in phosphatidylinositol, followed by phosphatidic acid, phosphatidylcholine, phosphatidylserine, lysophosphatidylcholine (lysolecithin), sphingomyelin, and phosphatidylethanolamine.

Acetylcholine (10^-5 M)in the presence of eserine (10^-5 M) produced a 3-fold increase in catecholamine release and stimulated the incorporation of ³²P into phosphatidic acid (3.4-fold), phosphatidylinositol (2.7-fold), and phosphatidylcholine (1.4-fold).

The uptake of orthophosphate-³²P into the chromaffin tissue, as well as the specific activities and tissue levels of orthophosphate and nucleotides, were not modified upon acetylcholine stimulation.

Glycerol-1-¹⁴C was incorporated into all the individual phospholipids, but, in contrast to ³²P incorporation, acetylcholine stimulation did not increase the incorporation of glycerol-1-¹⁴C into phospholipids.

No differences were observed in time total and individual phospholipid contents between control and stimulated slices.

The time course of the ³²P incorporation into phosphatidic acid and phosphatidylinositol in response to acetylcholine stimulation suggested that phosphatidic acid acts as a precursor in the synthesis of phosphatidylinositol in this tissue.

The possible mechanism of time action of acetylcholine on the phospholipid turnover of the adrenal medulla is discussed.

Note:
ACKNOWLEDGMENTS I wish to acknowledge time support and encouragement of Dr. M. Nickerson, and the technical assistance of Mr. S. Iu and Mr. A. Markert. I am also grateful to Dr. A. Tenenhouse for reading the manuscript.