182
JAMES K. GRANT
Estrogens excreted in the urine by the horse have been studied extensively (91). The principal substances present are estrone, equilin
(XXX), and equilenin (XXXI). Other related substances are excreted
in minor amount. It is remarkable that estrogens are present in astonishingly large amounts in the genital glands of certain male mammals.
HO
1 ^
(XXX)
(XXXI)
The richest known source is the testis of the horse, and stallion urine
actually contains more estrogenic material than that of pregnant mares.
The B ring unsaturated estrogenic steroids have so far been found only
in the horse. A trace of an equilenin-like substance, found in a feminizing adrenal tumor removed from a man, unfortunately could not be
fully identified for lack of material (92).
Estradiol-17« which has not been found in man has been isolated or
detected in the urine of horses, rabbits, goats, young calves, and pregnant cows.
It is remarkable that estrone and estriol occur in plants (93). Pure
crystalline estrone has been isolated from palm kernels and estriol from
willow flowers.
Heard (94) has studied the biosynthesis of estrogenic steroids from
C
14 -labeled precursors in the pregnant mare in vivo and observed that
acetate is incorporated into the three principal estrogens of this species.
More acetate is incorporated into estrone than into the B ring unsaturated estrogens, suggesting that acetate is utilized in the synthesis
of the saturated alicyclic part of the molecule only and that estrone is
not a precursor of equilin and equilenin. The utilization of acetate in
the synthesis of estrone was ten times greater than in the synthesis of
maternal blood cholesterol, and from this it was concluded that cholesterol from the maternal side is unlikely to be a precursor of estrogen.
Cholesterol from the fetal side of the placenta contained much more
radioactivity and might act as precursor of estrogens in the fetus. Unfortunately in these investigations insufficient consideration was given
to the way in which the specific activity of the estrogens and their precursors vary with time, nor was account taken of the fact that the
cholesterol probably occurs in metabolic pools which may not be in
equilibrium with one another so that, whereas the blood cholesterol
JAMES K. GRANT
Estrogens excreted in the urine by the horse have been studied extensively (91). The principal substances present are estrone, equilin
(XXX), and equilenin (XXXI). Other related substances are excreted
in minor amount. It is remarkable that estrogens are present in astonishingly large amounts in the genital glands of certain male mammals.
HO
1 ^
(XXX)
(XXXI)
The richest known source is the testis of the horse, and stallion urine
actually contains more estrogenic material than that of pregnant mares.
The B ring unsaturated estrogenic steroids have so far been found only
in the horse. A trace of an equilenin-like substance, found in a feminizing adrenal tumor removed from a man, unfortunately could not be
fully identified for lack of material (92).
Estradiol-17« which has not been found in man has been isolated or
detected in the urine of horses, rabbits, goats, young calves, and pregnant cows.
It is remarkable that estrone and estriol occur in plants (93). Pure
crystalline estrone has been isolated from palm kernels and estriol from
willow flowers.
Heard (94) has studied the biosynthesis of estrogenic steroids from
C
14 -labeled precursors in the pregnant mare in vivo and observed that
acetate is incorporated into the three principal estrogens of this species.
More acetate is incorporated into estrone than into the B ring unsaturated estrogens, suggesting that acetate is utilized in the synthesis
of the saturated alicyclic part of the molecule only and that estrone is
not a precursor of equilin and equilenin. The utilization of acetate in
the synthesis of estrone was ten times greater than in the synthesis of
maternal blood cholesterol, and from this it was concluded that cholesterol from the maternal side is unlikely to be a precursor of estrogen.
Cholesterol from the fetal side of the placenta contained much more
radioactivity and might act as precursor of estrogens in the fetus. Unfortunately in these investigations insufficient consideration was given
to the way in which the specific activity of the estrogens and their precursors vary with time, nor was account taken of the fact that the
cholesterol probably occurs in metabolic pools which may not be in
equilibrium with one another so that, whereas the blood cholesterol