Serum prolactin levels in castrated rams at various times of the year and during treatment with androgens or oestrogen.

Prolactin concentrations were measured in serum from wethers at various times of the year before and during treatment with testosterone proprionate, dihydrotestosterone propionate, 19-hydroxytestosterone dipropionate and oestradiol dipropionate. Levels of prolactin in serum were lower in untreated wethers during short (October) than during long (April-August) days. Seasonal differences persisted throughout the experiment but became less obvious during tretment with oestradiol dipropionate and 19-hydroxytestosterone dipropionate, both of which raised prolactin concentrations. Neither testosterone propionate nor dihydrotestosterone propionate altered the levels of prolactin.