Factors regulating sterol biosynthesis in the rat pineal gland in vitro.

The effects of hormones, feeding and photoperiod on pineal sterol biosynthesis were studied in rat pineal glands incubated with 1-14C acetate. The rate of sterol biosynthesis was 7.1 nmol/g/2 h. A high synthesis rate was observed during mid-dark of a 12:12 LD cycle and under constant light. Melatonin, testosterone, and glucagon had no effect on sterol synthesis whereas estradiol increased it and insulin and norepinephrine treatments decreased it. Increased cAMP levels resulting from dibutyryl cAMP and theophylline were also found to be inhibitory. Dietary cholesterol did not alter the rate of sterol biosynthesis but 24 h fasting depressed sterol synthesis significantly. It can be concluded that hormones and substrate availability may be involved in the regulation of pineal sterol biosynthesis.