Differential effect of pre- and postnatal litter size reduction on body weight and development of stress response in the rat.

The postnatal development of pups belonging to the small, prenatally reduced litters (PRN) was compared to that of pups of the postnatally reduced litters (PST) and to that of pups of intact, normal-size litters (CON). Body adrenal and pituitary weight gain as well as maturation of the pituitary-adrenal system were enhanced in the PRN and PST pups as compared to the CON pups in the 3 postnatal weeks. However, significant differences in some data between the PRN and PST pups were found, indicating the more pronounced beneficial effect of the prenatal reduction of litter size. The postnatal litter size reduction abolished the weight gain of the testes. The prenatal reduction of litter size resulted in a similar, although less pronounced negative effect.

Failure of the metopirone (Su4885) suppressed fetal adrenal glands to maintain corticosterone concentration of adrenalectomized pregnant rats.

Plasma corticosterone concentrations were measured following adrenalectomy of pregnant rats on the last day of gestation. Plasma corticosterone concentrations decreased 40 and 60 min after adrenalectomy by 36 and 32%, respectively, and regained the preoperative concentration 2 h following operation. When the fetuses were injected with an inhibitor of 11beta-steroid hydroxylase (Su4885) plasma corticosterone concentrations decreased 40, 60 and 120 min following adrenalectomy by 63, 67 and 71%, respectively. The results strongly suggest that the fetal adrenal glands are the source of plasma corticosterone in adrenalectomized pregnant rats.