Influence of Protein—Calorie Malnutrition on the Circadian Rhythm of Pineal Melatonin in the Rat

Pineal melatonin was measured over a 24-hr period in 50-day-old Sprague-Dawley male rats that had been fed a low-protein diet for 30 days and in a group of age-matched controls that were maintained for the same period on a standard laboratory chow. The patterns of melatonin secretion were similar in both groups. The highest content and concentrations were recorded during the dark phase of the 1ight:dark cycle, while the lowest were measured after the onset of light. At each of the time intervals studied, less of the antigonadotrophin was present within the pineal glands of the malnourished rats.