3. LIPIDS: STEROID METABOLISM
173
less attention has been paid to the steroids in spermatic vein blood, and
almost nothing is known of the steroids that occur in the ovarian secretion. It is for example often assumed that estradiol-17ß (XXVII) is the
estrogenic hormone in man and some other species without any direct
evidence that this substance is actually secreted by the ovary.
The second aspect of the problem of steroid hormone biosynthesis,
the way in which the hormones are formed in the cells of the endocrine
glands, has been intensively studied during the past decade. Experiments with endocrine tissues in vitro have been of value in indicating
steroid transformations that can occur and in suggesting possible intermediates between the hormones and cholesterol, which appears to be a
common precursor. Many of these experiments have been performed
with surviving endocrine tissues from the larger domestic animals such
as the ox, sheep, and swine, and while it is freely admitted that the
indications obtained from such experiments must be confirmed by
studies of hormone biosynthesis in vivo, such studies are not always
convenient to perform on large animals. The work of the late R. D. H.
Heard on the biosynthesis in vivo of steroid hormones by the pregnant
mare (Section I,B,3,fo) is outstanding, and it is most important that
such difficult and expensive experiments should be confirmed and extended.
2. Biosynthesis of Adrenocortical Steroids*
a. The Chemical Nature and Physiological Activity of the Adrenocortical Secretion. Chemical examination (42) of the adrenals of oxen
and swine revealed the presence of many steroids but gave no indication of which substances are actually secreted by the gland. Some of
the substances found may be hormone precursors or metabolites or
artifacts formed post mortem or during working up. The solution to
this problem was provided by the study of adrenal venous blood based
on Vogt's (41) technique and on the perfusion studies of Pincus' group
using the large (20 gm.) cow adrenal (43). The latter work was undertaken originally in order to identify steroids in the adrenocortical secretion, but was subsequently used to obtain information on possible precursors and their chemical transformations in the gland. (Fig. 3.)
* There is no satisfactory definition of adrenocortical steroids. These steroids are
usually regarded as 21-carbon compounds having oxygen substituents at C-3, C-20,
and C-21 and sometimes in other positions. There is, however, direct or indirect
evidence that the adrenal cortex also produces C 19 steroids (adrenal "androgens")
and C 18 steroids (estrogens). Attempts at classification are complicated by recent
observations that under some circumstances the adrenal cortex will secrete 21-deoxy
steroids and that the testes may under certain circumstances oxidize steroids in the
C-21 position.
173
less attention has been paid to the steroids in spermatic vein blood, and
almost nothing is known of the steroids that occur in the ovarian secretion. It is for example often assumed that estradiol-17ß (XXVII) is the
estrogenic hormone in man and some other species without any direct
evidence that this substance is actually secreted by the ovary.
The second aspect of the problem of steroid hormone biosynthesis,
the way in which the hormones are formed in the cells of the endocrine
glands, has been intensively studied during the past decade. Experiments with endocrine tissues in vitro have been of value in indicating
steroid transformations that can occur and in suggesting possible intermediates between the hormones and cholesterol, which appears to be a
common precursor. Many of these experiments have been performed
with surviving endocrine tissues from the larger domestic animals such
as the ox, sheep, and swine, and while it is freely admitted that the
indications obtained from such experiments must be confirmed by
studies of hormone biosynthesis in vivo, such studies are not always
convenient to perform on large animals. The work of the late R. D. H.
Heard on the biosynthesis in vivo of steroid hormones by the pregnant
mare (Section I,B,3,fo) is outstanding, and it is most important that
such difficult and expensive experiments should be confirmed and extended.
2. Biosynthesis of Adrenocortical Steroids*
a. The Chemical Nature and Physiological Activity of the Adrenocortical Secretion. Chemical examination (42) of the adrenals of oxen
and swine revealed the presence of many steroids but gave no indication of which substances are actually secreted by the gland. Some of
the substances found may be hormone precursors or metabolites or
artifacts formed post mortem or during working up. The solution to
this problem was provided by the study of adrenal venous blood based
on Vogt's (41) technique and on the perfusion studies of Pincus' group
using the large (20 gm.) cow adrenal (43). The latter work was undertaken originally in order to identify steroids in the adrenocortical secretion, but was subsequently used to obtain information on possible precursors and their chemical transformations in the gland. (Fig. 3.)
* There is no satisfactory definition of adrenocortical steroids. These steroids are
usually regarded as 21-carbon compounds having oxygen substituents at C-3, C-20,
and C-21 and sometimes in other positions. There is, however, direct or indirect
evidence that the adrenal cortex also produces C 19 steroids (adrenal "androgens")
and C 18 steroids (estrogens). Attempts at classification are complicated by recent
observations that under some circumstances the adrenal cortex will secrete 21-deoxy
steroids and that the testes may under certain circumstances oxidize steroids in the
C-21 position.