Daily rhythm in secretion of prolactin in androgenized female rats

Androgen-sterilized female rats were obtained by administering 10 micrograms testosterone propionate to pups on day 2 after birth. In contrast with ovariectomized adults, androgenized adult female rats are incapable of responding to cervical stimulation by secreting prolactin in the nocturnal surge pattern. In spite of the loss of this pattern the androgenized female rats still exhibited a daily circadian rhythm of prolactin secretion with afternoon levels three times higher than those after midnight.