An effect of estradiol and testosterone on the calcium pump activity and phospholipid fatty acid composition of rat liver microsomes.

Castration of the male rat resulted in a 28% reduction of the specific activity of liver microsomal calcium uptake, three weeks after castration. Treatment of the castrated animals with testosterone during this period returned calcium uptake to control levels. Treatment with estradiol resulted in a reduction of calcium uptake to a level less than 25% of that seen in the normal male. Although testosterone treatment had only a small effect on the fatty acid composition of liver microsomal phospholipids in the castrated male, there were significant changes of linoleic acid (18:2) in phosphatidylcholines and of palmitic acid (16:0) in phosphatidylethanolamines, when compared to the untreated castrated male rat. Administration of estradiol to the castrated male rat resulted in a marked decrease of palmitic acid (16.0) and linoleic acid (18.2) in all three phospholipid fractions studied. Stearic acid (18.0) was significantly increased in the phosphatidylcholines and phosphatidylethanolamines by estradiol treatment. The phospholipid and calcium uptake changes seen after treatment of the castrated rat with testosterone or estradiol are consistent with the sex-related differences observed in the intact, adult rat liver microsomes.