Effect on pituitary and on embryological development: on testis and ovary: on accessory generative organs of male and female. Co-operation and antagonism between progestin and other gonadal hormones. Similarities in action between progesterone, androgen, oestrogen and adrenal cortical hormones.

THE natural history of the corpora lutea or luteal glands having been discussed in a general way, the biological activities of their special secretions may now be considered. To avoid giving the impression that progesterone is the only effective luteal hormone, the term progestin will be used in a generic sense to include cognate compounds.

The Pituitary

Progestin, like the other gonadal hormones, acts either directly on individual organs, or indirectly affects them through the changes which it induces in the anterior lobe of the pituitary gland. These pituitary changes have been dealt with already (pp. 57,91) and need no further reference here except perhaps to recall the fact that progestin arrests the output of FRH and so interferes with the maturation of ovarian follicles and the initiation of ovarian cycles. For this purpose relatively large amounts are required.

Embryological Development

It will be remembered that both oestrogen and androgen have a pronounced influence over the development of the reproductive organs. Unfortunately we are not in a position to say much about the effects of progestin on the immature organs, for little experimental inquiry has been made into the subject. Burrows (1939 c) found that progesterone, like androgen and oestrogen, when injected into newborn female rats and mice, causes hypospadias, the ventral wall of the clitoris becoming deficient so that the opening of the urethra instead of being at its apex is at its base, level perhaps with the margin of the vaginal orifice. Burrows found also that, when persistently given to young male rats, progesterone checks the development of the testes and prevents their descent into the scrotum. Much has been done to determine what influence progesterone exerts on the development of the mamma (p. 430). Beyond these observations we know little about the effects which progesterone may have upon the growth of the reproductive organs in early life.