PHOSPHOLIPID METHYLATION DECREASES IN HUMAN CHORIONIC GONADOTROPIN-INDUCED DESENSITIZED RAT LEYDIG-CELLS

Phospholipid methylation in Leydig cells from desensitized rats was st udied. The incorporation of L-[methyl-H-3]methionine into phospholipid s in intact Leydig cells decreased when animals were injected with a s ingle high dose of human chorionic gonadotrophin (hCG). This effect wa s detected on the first day after hCG injection and remained up to 12 days after treatment. The inhibition was not due to a reduced uptake O f L-[methyl-H-3]methionine. A decreased phospholipid methylation with unaltered phospholipid methyltransferase activity was observed on days 1, 6 and 12 after the hCG. On day 3 after hCG injection, phospholipid methyltransferase activity and phospholipid methylation in intact Ley dig cells were both inhibited by 40%. Also, a minimal amount of LH fre e receptors and the lowest number of total receptors was observed at t his time. Thus, a relationship between the reduced enzymatic activity and the maximal decrease in LH surface receptors is suggested. In addi tion, the decreased incorporation of L-[methyl-H-3]methionine into pho spholipids on days 1, 6 and 12 after hCG injection, could be associate d with other cellular changes related to the desensitization process.