Hormonal effects on mitotic rhythm in the epidermis of the red-spotted newt

Abstract

The mitotic indices of epidermal cells in the red-spotted newt were measured at 3- or 4-hr intervals throughout 24-hr periods under a variety of hormonal conditions. In intact control newts maintained on a photoperiod of 16 hr of light/8 hr of darkness, a peak in mitotic activity was observed during the dark hours and a second smaller (but not statistically significant) peak was seen during the light hours. Inversion of the light cycle induced a new and more rapid rhythm. The basic rhythm was accentuated by autografting the pituitary gland to an ectopic site and also by the administration of thyroxine to intact animals. Hypophysectomy and administration of the prolactin-inhibiting drug, ergocornine, to auto-grafted animals greatly reduced the rate of epidermal proliferation and apparently reduced the peaks until they were no longer detectable. Injection of ovine prolactin into hypophysectomized or intact animals elevated the overall mitotic index and obscured or altered the mitotic rhythm. Removal of the rhyroid gland or administration of thiourea also altered the rhythm, but treatment with ACTH produced no detected effect. Apparently the basic rhythm of epidermal mitosis can be overridden or altered either by hormonal factors that increase or by ones that decrease the overall rate of cellular proliferation.