Characteristics of 4-Day Infradian Biorhythms in Mature Male Wistar Rats after Pinealectomy.

We studied the effect of pinealectomy on the parameters of 4-day infradian biorhythms in mature male Wistar rats. It was shown that pinealectomy did not change the period and phase of infradian biorhythm of total locomotor activity, serum concentrations corticosterone and testosterone, and mitotic index of esophageal epithelium. No significant changes in the number of nucleated cells in the spleen of pinealectomized animals in comparison with intact animals were found. The amplitude of biorhythms of locomotor activity and corticosterone and testosterone concentrations did not significantly change in pinealectomized animals. Despite the important role of the epiphysis in the regulation of circadian biorhythms in mammals, this organ is not the main synchronizer of infradian biorhythms of glucocorticoid and sex hormones in male Wistar rats.