Decrease in high-density lipoprotein cholesterol after administration of melatonin-free pineal extract in the rat.

The work was focused on the effect of the pineal extract on HDL-cholesterol alongside the effect of the same extract on serum cholesterol and testosterone in the rat under basal conditions. HDL-cholesterol is utilized in the rat, preferentially by the Leydig cells for steroidogenesis. Administration of melatonin-free pineal extract, in doses of 2 ml/day/animal along 3, 6 and 12 days caused a statistically significant decrease in HDL-cholesterol of 19, 21 and 20%, respectively. The same depressor effect occurred 4 hr following a unique injection of pineal extract (-25%, p less than 0.001). Cholesterolemia decreased significantly alongside with HDL-cholesterol (14, 18, and 16% after 3, 6 and 12 days and 18% after 4 hr). The effect of the pineal extract on testosterone tested in only two experiments was to depress it significantly by 43% after 4 hr and 45% after 6 days of treatment. The decrease in testosterone level following the decrease of its major precursor, cholesterol, is discussed.