Effect of illumination on different lipid fractions of rat pinealocytes. A histochemical study

Total lipids and phospholipids of pineal glands of female rats maintained under a diurnal rhythm of 12 hr of light and 12 hr of darkness, continuous illumination for 2 days or 4 weeks and constant darkness for 2 days or 4 weeks were studied histochemically. The controlled chromation of Elftman followed by Sudan black B to visualize total lipids and by hematoxylin to reveal phospholipids was used. Staining was made on paraffin embedding and vibratome sections. Total lipids showed a significant decrease under constant illumination for 2 days or 4 weeks, but phospholipids, which suffered a dramatic decrease in rats maintained under constant light for 4 weeks, remained without significant variation after 2 days of treatment. Thus, the lipid decrement after 2 days of constant light seems to be due to another lipid fraction, probably triglycerides. Total lipids and phospholipids remain almost unchanged after 2 days or 4 weeks of constant darkness. The solubility in lipid solvents was considerably increased for phospholipids after 4 weeks and for the non-phospholipidic fraction after 2 days of permanent light. This suggests that continuous illumination induces a change in the solubility of lipid droplets components affecting different kinds of lipids depending on the light stimulation.