222
WILLIAM C. YOUNG
from laying hens (283). Evidence based on chromatographic mobility,
ultraviolet spectrophotometry, and chemical reaction indicates that the
principal estrogens in ovarian tissues of the fowl are estrone, estradiol,
and estriol (305). The formation of an insoluble digitomide in the
phenolic steroid fraction from the droppings of fowl suggested that
estrone is the biologically active form (306).
Much attention has been given to the cellular origin of the gonadal
hormones in birds. As in the work with animals in other phyla, suggestive
information was obtained from correlations between seasonal reproductive activity and the quantity and microscopic appearance of gonadal
tissue. More recently reliance has been placed on histochemical studies.
In general, steroid-secreting cells and steroid-containing substances are
indicated by their content of osmophilic cholesterol-containing lipids.
Qualitative distinctions are based on other criteria, for the most part
the presence of cells in tissues known from physiologic or morphologic
tests to be secreting estrogens, androgens, or gestagens, but also from
supplementary chromatographic studies as in the work of Lofts and
Marshall (244) on the content of the postnuptial testicular tubules, and
from bioassays such as that developed by Hooker and Forbes (307, 308).
Within male birds, Leydig or testicular interstitial cells have long
been considered to be the principal source of androgen (230, 299). The
association of a Sertoli cell tumor near the gonadal area with the feminization of a Brown Leghorn capon was taken as evidence that Sertoli
cells secrete estrogen (309). The source of the progesterone found in
the plasma of cocks (282) is unknown. Participation of the tubules in the
secretion of steroids has been demonstrated by investigators who have
examined the testes of a number of species of birds at the conclusion of
spermatogenesis and prior to the autumnal or postnuptial recrudescence
of reproductive behavior. The latter is seen in males and females of
many birds and is well described by several British colleagues (233,
252, 256, 257, 261, 310-312). In several widely unrelated species there
is a massive cholesterol-positive steatogenesis in the seminiferous tubules.
The tubules collapse, and the unshed germinal material and apparently
the syncytial Sertoli cytoplasm are converted to cholesterol-positive
lipids (230, 245, 312). Tests of the possibility that these metamorphosed
tubules contain progestin which might have an endocrine function were
made by Lofts and Marshall (244), who analyzed the tubular liquid by
paper chromatography and by bioassay of the progestin content. As had
been predicted, progestins appeared in the chromatograms of extracts
from these tests. A role of this hormonal substance in incubation behavior and the feeding of the young and in the limited autumnal sexual
activity has been suggested (195, 233, 244), but thus far these possibili-
WILLIAM C. YOUNG
from laying hens (283). Evidence based on chromatographic mobility,
ultraviolet spectrophotometry, and chemical reaction indicates that the
principal estrogens in ovarian tissues of the fowl are estrone, estradiol,
and estriol (305). The formation of an insoluble digitomide in the
phenolic steroid fraction from the droppings of fowl suggested that
estrone is the biologically active form (306).
Much attention has been given to the cellular origin of the gonadal
hormones in birds. As in the work with animals in other phyla, suggestive
information was obtained from correlations between seasonal reproductive activity and the quantity and microscopic appearance of gonadal
tissue. More recently reliance has been placed on histochemical studies.
In general, steroid-secreting cells and steroid-containing substances are
indicated by their content of osmophilic cholesterol-containing lipids.
Qualitative distinctions are based on other criteria, for the most part
the presence of cells in tissues known from physiologic or morphologic
tests to be secreting estrogens, androgens, or gestagens, but also from
supplementary chromatographic studies as in the work of Lofts and
Marshall (244) on the content of the postnuptial testicular tubules, and
from bioassays such as that developed by Hooker and Forbes (307, 308).
Within male birds, Leydig or testicular interstitial cells have long
been considered to be the principal source of androgen (230, 299). The
association of a Sertoli cell tumor near the gonadal area with the feminization of a Brown Leghorn capon was taken as evidence that Sertoli
cells secrete estrogen (309). The source of the progesterone found in
the plasma of cocks (282) is unknown. Participation of the tubules in the
secretion of steroids has been demonstrated by investigators who have
examined the testes of a number of species of birds at the conclusion of
spermatogenesis and prior to the autumnal or postnuptial recrudescence
of reproductive behavior. The latter is seen in males and females of
many birds and is well described by several British colleagues (233,
252, 256, 257, 261, 310-312). In several widely unrelated species there
is a massive cholesterol-positive steatogenesis in the seminiferous tubules.
The tubules collapse, and the unshed germinal material and apparently
the syncytial Sertoli cytoplasm are converted to cholesterol-positive
lipids (230, 245, 312). Tests of the possibility that these metamorphosed
tubules contain progestin which might have an endocrine function were
made by Lofts and Marshall (244), who analyzed the tubular liquid by
paper chromatography and by bioassay of the progestin content. As had
been predicted, progestins appeared in the chromatograms of extracts
from these tests. A role of this hormonal substance in incubation behavior and the feeding of the young and in the limited autumnal sexual
activity has been suggested (195, 233, 244), but thus far these possibili-