Prolactin influences the circadian rhythm of lipogenesis in primary cultured hepatocytes.

Hepatocytes from male Syrian hamsters were cultured in the presence of insulin and assayed for lipogenesis by following (14C)acetate incorporation into total cell lipid at 4 hourly intervals over a 48-h period. Circadian rhythms of lipogenic activity were observed on days 2 and 3 of culture. Although the phases of the rhythms were similar, the amplitude of the peak levels of lipogenesis declined from day 2 to 3. Addition of prolactin to the culture reversed this decline when introduced at specific times relative to the lipogenic peaks. Prolactin more than doubled lipogenesis only at the daily peaks of lipogenic activity and only when added to culture 20 h before the times of peak lipogenesis. The results are the first to demonstrate important roles for circadian rhythms and a direct prolactin stimulation in the regulation of lipogenesis in primary hepatocyte culture.