Effect of neonatal undernutrition on serum follicle-stimulating hormone levels and ovarian development in the female rat.

1. Female rats were undernourished from birth through replacement for 12 h/d of the lactating mother by a nipple-ligated mother. This resulted in slow growth so that 22 d of age the body-weights equalled those of well-nourished animals at 14 d. 2. At 14, 17, 20 and 22 d groups of eight to ten animals each of undernourished and well-nourished rats were autopsied, serum follicle-stimulating hormone (FSH) concentration was determined by radioimmunoassay, uteruses were weighed and ovaries examined by light microscopy. 3. Undernutrition caused a 3-4 d delay in the third-week drop in serum FSH and in ovarian development as indicated by the numbers of antral follicles and by the maximal diameter of the ovaries and of the largest follicles. 4. It is postulated that the effect of undernutrition on serum FSH may be due to delayed increase in ovarian feedback effectiveness, which may be the result of either the retardation in ovarian development or a continued high level of serum oestrogen-binding protein. It remains uncertain through which mechanisms(s) undernutrition brings about delayed onset of puberty.