Hypophysectomized rats depend on residual prolactin for survival.

Hypophysectomized (Hypox) female Fischer 344 rats had 10-20% lactogenic activity in their serum when compared to controls by the Nb2 lymphoma proliferation assay. If such animals were treated daily with a rabbit antirat PRL serum, their serum lactogenic activity diminished further; severe anemia and immunological anergy developed; and death occurred within 8 weeks. In contrast, untreated Hypox animals increased gradually their serum lactogenic activity, starting on the 7th week after pituitary removal, which rose up to 50% of control levels by week 9. Hypox animals showed normochromic normocytic anemia, a grossly reduced immunocompetence, decreased body, thymus, spleen, adrenal, and ovary weights, and decreased DNA and RNA synthesis in the thymus, spleen, and bone marrow. However, the condition of Hypox animals did not deteriorate further over the 9-week experimental period. All the hematological deficiencies and decrease in organ weights observed in Hypox rats were normalized after grafting with syngeneic pituitaries (SPG). These effects of SPG could be inhibited by additional treatment with antirat PRL serum. Treatment of Hypox animals with ovine PRL had a restoring effect similar to SPG, which was not inhibited by additional antirat PRL serum treatment. Rat and ovine PRL and GH and human placental lactogen all stimulated the incorporation of 3H-thymidine by rat bone marrow cells in vitro. These results indicate that PRL has a multiple trophic effect and is capable of maintaining vital bodily functions for long periods of time.