Effects of unilateral ovariectomy before and after mating on fetal and placental growth in rats.

Unilateral ovariectomy was carried out on rats either 8 days after mating (ULO-A) or 4-6 weeks before mating (ULO-B) and the effects on fetal and placental weights were examined at days 13, 16, and 22 of gestation. ULO-A caused initial fetal and placental hypotrophy at day 13, but thereafter placental weights increased to 123% and 132% of control values at days 16 and 22, respectively. Fetal weights were also 9% heavier in the ULO-A rats at day 22. The ULO-B stimulus resulted in placental but not fetal hypotrophy at day 13 and placental hypertrophy at days 16 and 22. Although the results of the two stimuli were generally similar, it is argued that the mechanisms underlying the ULO-A results were primarily endocrinological whereas those for the ULO-B results were due to crowding of conceptuses in one uterine horn and the subsequent compensatory responses.