AJP - Endocrinology and Metabolism, Vol 264, Issue 4 E534-E540, Copyright © 1993 by American Physiological Society
Time of day of birth and absence of endocrine and uterine contractile activity rhythms in sheep
E. M. Apostolakis, K. E. Rice, L. D. Longo, M. Seron-Ferre and S. M. Yellon
Department of Physiology, School of Medicine, Loma Linda University, California 92350.
To determine whether 24-h rhythms characterize hormone secretion and
uterine activity in the pregnant sheep, blood samples were drawn every 1-4
h for 48 h from ewes and fetuses from day 120 of gestation to term.
Repetitive 24-h rhythms were absent for cortisol, progesterone, and
prolactin in maternal and fetal circulation and for hourly mean uterine
contraction rate and amplitude. To test whether photoperiod or pineal
melatonin contributes to the absence of rhythms, pineal-intact and
pinealectomized ewes and their fetuses were studied in reverse photoperiod.
Again, there was little evidence to suggest 24-h endocrine rhythms except
for prolactin in two fetuses by cosinor analyses. Prolactin concentrations
were increased in pinealectomized ewes and their fetuses. In the apparent
absence of rhythms, 20 of 21 pineal-intact ewes gave birth at night;
however, 6 out of 7 pinealectomized ewes gave birth during the day. Thus
photoperiod and the maternal pineal gland profoundly influenced the time of
day of birth in the absence of circadian endocrine or uterine activity
rhythms.
