Abstract
Changes in serum prolactin levels from day 4 before parturition to 24 hr after it of primiparous Sprague-Dawley rats were investigated by radioimmunoassay. Serum prolactin levels rose on day 0 before parturition (1-6 hr before the beginning of parturition) and declined abruptly immediately after parturition (2-6 min after the end of parturition). Serum prolactin levels increased again thereafter and were maintained at a little higher levels between 4 and 7 hr after parturition than on day 10 of lactation. The levels rose further between 9 and 10 hr after parturition to higher levels than on day 0 before parturition. Serum prolactin levels dropped thereafter and were maintained approximately at the level on day 10 of lactation until 24 hr after parturition. There existed no correlations between either two of the following values; time required for parturition, litter size, serum prolactin levels on day 0 before, at 0 and 24 hr after parturition. The coefficient of variation of serum prolactin value examined at each time was always higher than that on day 10 of lactation.
