[Effect of constant light on the circadian rhythm of prolactin (author's transl)]

The different effects of equal periods of constant light (from days 1-65 or 70-135) upon the circadian rhythm of prolactin in male rats have been studied. Plasmatic levels of hormone have been analyzed at 5.00, 9.00, 12.00, 17.00, 21.00 and 24 h. 65 and 135 day-old controls on a 12 h light/12 h darkness schedule show PRL surges at 17.00 h. These surges disappear in both groups when submitted to constant light. A global increase of PRL levels can be observed only in 135 day-old rats, which disappears 15 days after castration. This indicates testicular involvement in the hyperprolactinemia induced by constant light.