Biology of Reproduction, Vol 10, 480-486, Copyright © 1974 by Society for the Study of Reproduction

Function of the Pineal Gland of the Rat during Progestation: Alterations in HIOMT Rhythmicity

¹ Department of Physiology and Cell Biology, University of Kansas, Lawrence, Kansas 66045

Pineal HIOMT activity was measured following induction of pseudopregnancy by uterine cervical stimulation in the rat. The diurnal pattern of enzyme activity was altered within 2 days and was significantly different from that measured during the estrous cycle. Though diurnal rhythmicity persisted, the change in activity could be accounted for by a modification of one of two hypothetical component rhythms which describe the HIOMT pattern. No change in the mean rate of enzyme activity or of the hypothetical amplitudes of the component rhythms was noted. Ovariectomy, performed after the induction of pseudopregnancy did not alter the pseudopregnant pineal rhythms, but caused a decrease in the mean rate of enzyme activity. Ovariectomy, performed prior to cervical stimulation, did not prevent the development of the pseudopregnancy-pattern of HIOMT activity in the pineal gland. In this instance also, the mean rate of enzyme activity was less than that in intact rats. These results are consistent with a previously proposed model for pineal gland function in relation to reproductive activity.