AJP - Endocrinology and Metabolism, Vol 248, Issue 3 269-E273, Copyright © 1985 by American Physiological Society
Effect of conceptus number, hysterectomy, and progesterone on prolactin surges in rats
P. A. Tonkowicz and J. L. Voogt
Mating induces two daily surges of prolactin (PRL) secretion in the rat.
Termination of the diurnal and nocturnal surges coincides with the
development of the placenta and the secretion of rat placental lactogen
(RPL). The number of conceptuses present was altered to induce changes in
RPL levels in the blood. The presence of one intact viable conceptus is
sufficient to cause termination of the diurnal PRL surge. The presence of
one or zero conceptuses allowed resumption of the nocturnal surge after day
14, whereas presence of two or more conceptuses prevented the surge.
Hysterectomy on day 14 allowed the resumption of the nocturnal PRL surges
for 2 days and diurnal PRL surges for 3 days. Progesterone treatment
stimulated an additional third nocturnal PRL surge and blunted the
magnitude of the resuming diurnal surges. It is concluded that secretions
from the conceptus and progesterone contribute to the regulation of
prolactin during pregnancy.
