Some dietary and hormonal effects on maternal, foetal and placental weights in the rat.

Abstract

1. A negative correlation was found between the mean weight of an individual placenta and the number in a litter. Within the range examined and with the methods employed, no definite correlation between the mean weight of an individual foetus and litter size was established. 2. Reduction of the food intake to one-half or one-third during the last 6 days of pregnancy did not result in a decrease in the number and weight of foetuses and placentae. This was apparently brought about by drawing on the maternal reserves laid down during the first 14 days of pregnancy. Absence of protein from the diet during the last 6 days resulted in a very moderate decrease in foetal and placental weights. 3. Absence of the maternal adrenals or pituitary had no influence on foetal and placental weights. The decrease in maternal body weight after hypophysectomy was solely due to loss of appetite and could be prevented by giving the rats adequate amounts of food by stomach tube. 4. The increase in body weight during the first 14 days of pregnancy was maintained after removal of the foetuses as long as the placentae survived. The placentae also had a favourable effect on the maternal body weight in the absence of the foetuses, when the ovaries or adrenals or the pituitary or the pituitary and ovaries were removed, but not when both ovaries and adrenals were absent. The placental factor responsible for this effect appears to act through the ovaries or adrenals. 5. The increase in the weight of the ovaries during pregnancy was not affected by removal of the foetuses, foetuses and pituitary, or foetuses and adrenals. The adrenals of pregnant hypophysectomized rats were not heavier than those of non-pregnant hypophysectomized rats.