The Role of Prolactin in Lactating Rats by Passive Immunization

Abstract

Some of the physiological roles of prolactin (PRL) in lactating rats were studied by passive immunization. Antibody to rat PRL (A/S PRL) was produced in rabbits immunized with rat PRL. Then the sera of the rabbits were tested for the potency and specificity of antibody to PRL by double antibody radio‐immunoassay technique. One ml of antiserum was inferred to be capable of sufficiently neutralizing endogenous PRL in lactating rats. From the 5th day of postpartum, 11 rats were daily injected intraperitoneally with 1 ml of A/S PRL. In the control group, each of 7 rats was daily injected with 1 ml of normal rabbit serum (NRS). Most pups in the treated group died between the 16th and 20th postpartum days, but all pups in the control group grew normally. Serum oxytocin (OT) levels in the treated group were significantly increased, suggesting that mechanical stimulation of the nipples by pups might increase OT levels, presumably because a lack of PRL decreased milk production. Serum growth hormone (GH) levels in both groups were virtually identical, suggesting that GH could not compensate PRL during the period of passive immunization.