Biosynthesis of long-chain polyenoic acids from arachidonic acid in cultures of enriched spermatocytes and spermatids from mouse testis.

Primary spermatocytes (PS), round spermatids (RS) and condensing spermatids (CS) from mouse testes were enriched on Sta-Put 1 X g density gradients and cultured for 22 or 44 hr in the presence of [1-14C]arachidonate. Mass and radioactivity were measured by gas radiochromatography of constituent fatty acids of the various complex lipid classes fractionated by thin layer chromatography. Patterns and levels of incorporation were compared with those of whole testis, both in vitro and in vivo. The 20:4, 22:4, 22:5, 24:4 and 24:5 of the germinal cells contained levels of radioactivity in each lipid class which were consistent with an important role for the germinal cells in long-chain polyenoic acid (LCPA) metabolism. Cells which represented later stages of spermatogenesis (RS, CS) incorporated much higher percentages and absolute amounts of radioactivity into the fatty acids derived from 20:4 by elongation-desaturation pathways than did PS or whole testis in vitro. These differences were most pronounced in triacylglycerol of CS. Distributions of mass and radioactivity among lipid classes suggest synthesis of triacylglycerol by CS with a high degree of specificity for 22 or 24 carbon LCPA at the sn-3 position.