3. LIPIDS: STEROID METABOLISM
175
The result of these and other investigations indicate that C 2 i
steroids having oxygen substituents at C-ll and C-21 are characteristic
of the adrenal cortex. The principal substances of this nature present
in the adrenal venous blood of most species examined are hydrocortisone (XIII), corticosterone (XX), and aldosterone (XXI). The last
is present in very much smaller concentrations than the first two, possibly amounting to less than 1% of the total corticosteroid in the adrenal
venous blood of dogs; nevertheless it is of major physiological importance (44-46).
Administration of any one of these substances will reverse the widespread effects of adrenalectomy which ultimately result in death. They
influence many tissues and almost every aspect of intermediate metabolism, and it is unlikely that their biological activities are fully known.
A very useful summary of the voluminous literature on this aspect of
endocrinology is provided by Chester Jones (47). Each of these substances shows qualitatively the same effect on carbohydrate and electrolyte metabolism in test animals, but they differ remarkably in their
quantitative effects. Thus, hydrocortisone and corticosterone are predominantly "glucocorticoids," and aldosterone is by far the most active
substance influencing electrolyte and water metabolism.
h. The Proportions of Hydrocortisone and Corticosterone Formed.
No explanation can be offered for the occurrence in many species of
two hormones, hydrocortisone and corticosterone, of apparently similar
qualitative and quantitative biological activity. It is of course quite
possible that important differences in the biological activities of these
two hormones remain to be found. It is notable, however, that some
species, including the rat, rabbit, and mouse, seem able to dispense
with hydrocortisone.
The relative proportions of hydrocortisone and corticosterone are
reported to vary in different species (Table I). These results, however,
were obtained with relatively few individuals in any one species, and
there is evidence of considerable individual variation within one species.
Thus the hydrocortisone: corticosterone ratio has been reported to vary
from 10:1 to 1:1 in man and this may be related to the effect of endogenous corticotropin. In dogs selected at random, ratios ranging from
20:1 to 1.2:1 have been reported from one laboratory (50). Prolonged
administration of corticotropin will induce secretion of hydrocortisone
in the rabbit which does not normally secrete this substance in detectable amounts (51). Sex may influence the type of hormone secreted
since the steer appears to produce corticosterone also, but no hydrocortisone, whereas the cow secretes both hormones as judged by adrenal
perfusion experiments (54).
175
The result of these and other investigations indicate that C 2 i
steroids having oxygen substituents at C-ll and C-21 are characteristic
of the adrenal cortex. The principal substances of this nature present
in the adrenal venous blood of most species examined are hydrocortisone (XIII), corticosterone (XX), and aldosterone (XXI). The last
is present in very much smaller concentrations than the first two, possibly amounting to less than 1% of the total corticosteroid in the adrenal
venous blood of dogs; nevertheless it is of major physiological importance (44-46).
Administration of any one of these substances will reverse the widespread effects of adrenalectomy which ultimately result in death. They
influence many tissues and almost every aspect of intermediate metabolism, and it is unlikely that their biological activities are fully known.
A very useful summary of the voluminous literature on this aspect of
endocrinology is provided by Chester Jones (47). Each of these substances shows qualitatively the same effect on carbohydrate and electrolyte metabolism in test animals, but they differ remarkably in their
quantitative effects. Thus, hydrocortisone and corticosterone are predominantly "glucocorticoids," and aldosterone is by far the most active
substance influencing electrolyte and water metabolism.
h. The Proportions of Hydrocortisone and Corticosterone Formed.
No explanation can be offered for the occurrence in many species of
two hormones, hydrocortisone and corticosterone, of apparently similar
qualitative and quantitative biological activity. It is of course quite
possible that important differences in the biological activities of these
two hormones remain to be found. It is notable, however, that some
species, including the rat, rabbit, and mouse, seem able to dispense
with hydrocortisone.
The relative proportions of hydrocortisone and corticosterone are
reported to vary in different species (Table I). These results, however,
were obtained with relatively few individuals in any one species, and
there is evidence of considerable individual variation within one species.
Thus the hydrocortisone: corticosterone ratio has been reported to vary
from 10:1 to 1:1 in man and this may be related to the effect of endogenous corticotropin. In dogs selected at random, ratios ranging from
20:1 to 1.2:1 have been reported from one laboratory (50). Prolonged
administration of corticotropin will induce secretion of hydrocortisone
in the rabbit which does not normally secrete this substance in detectable amounts (51). Sex may influence the type of hormone secreted
since the steer appears to produce corticosterone also, but no hydrocortisone, whereas the cow secretes both hormones as judged by adrenal
perfusion experiments (54).