Circannual Rhythm of Free Fatty Acids and Diacylglycerols in 5‐Day‐Old Rat Cerebrum During Pentylenetetrazol‐Induced Convulsions

: Free fatty acids (FFA) and diacylglycerol (DG) content and composition in the cerebrum of 5‐day‐old rats were studied after pentylenetetrazol (PTZ)‐induced convulsions. A threefold increase in brain FFA was observed 30 min after PTZ injection in experiments carried out in spring. In contrast. a 50% decrease in FFA content was observed during summer. These changes were accounted for by saturated and monoenoic fatty acids, whereas arachidonic and docosahexaenoic acids were not affected during the convulsive episode in either season. The effect of PTZ on brain DG was much smaller than it was on FFA, and less sensitive to seasonal influence. However, DG released in the summer was significantly less enriched in arachidonic acid than in the spring. Levels of FFA and DG in untreated animals were found to be subject to a circannual rhythm. Both the levels of FFA and their degree of unsaturation (unsaturated fatty acids/total FFA) were highest in summer and lowest in winter. whereas the opposite was true for DG. Circannual variations in these metabolites may be the manifestation of a programmed biological calendar regulating enzymes of brain lipid metabolism in homeotherms that under natural conditions must adapt to changing environmental temperatures.