6. ADRENAL STEROIDS AND ACTH
333
intact trout, Salmo gairdneri, cortisol and corticosterone caused a decline
in plasma sodium concentration and increased water and sodium content
of parietal muscle. Repeated injection of aldosterone induced hyponatremia and moderate hyperkalemia (Holmes and Butler, 1%). Similarly in the eel, Anguillu anguillu, maintained in freshwater, cortisol in
high doses induced hyponatremia and increased muscle water content
while muscle sodium concentration declined. Aldosterone, given in smaller
doses, had no effect ( D. K. 0. Chan et al., 196%).
From the information derived from these injection studies, it is not
possible to conclude that adrenocorticosteroids have an obvious physiological role in the control of osmoregulation. In fact, these steroids often
produced deleterious effects in intact animals. Moreover, on the basis that
injection of adrenal steroids did not promote the adaptation of stenohaline marine teleost fish to freshwater, it has been argued that adrenocorticosteroids had no role to play in osmoregulation in fish (Lockley,
1957; Edelman et al., 1960). It must be remembered that in general hormones do not initiate a physiological process, but they may take a vital
part in the control of the efficiency or speed of such a process when it has
been initiated. Many studies have employed doses of steroids of large
magnitude, and under normal conditions, the hormone is present in the
plasma in microgram amounts. The rate of secretion of steroid hormone
has been variously estimated to be about 2050 fig/lOO g body weight per
day. Exogenous hormones, especially those that do not naturally occur in
the animal, may produce spurious effects or may directly inhibit the action
of the naturally occurring equivalent hormone. A more informative experimental approach would be to test the hormones in animals without
endogenous secretions. This can be done either by surgical adrenalectomy or by pharmacological inhibition of the adrenal cortex with drugs.
Surgical adrenalectomy has been accomplished in a few species of
elasmobranchs. Hartman et al. (1944) found no significant changes in
plasma composition after removal of the adrenal cortex from the skate,
although Chester Jones (1957) recalculated their data to indicate at least
an elevation of plasma potassium concentration. More recently, Idler and
Szeplaki (1968) have in many ways confirmed the earlier work, in that
sodium, potassium, magnesium, and urea plasma levels were unchanged.
They found, however, an increase in plasma calcium concentration.
In teleost fish, owing to the special anatomical arrangement of the
adrenocortical tissue in the head kidney and cardinal veins, surgical
adrenalectomy has proved difficult. To date, this operation has been successful only in two species, namely, the goldfish (Etoh and Egami, 1963)
and the eel (Chester Jones et al., 1964). The latter species is euryhaline
333
intact trout, Salmo gairdneri, cortisol and corticosterone caused a decline
in plasma sodium concentration and increased water and sodium content
of parietal muscle. Repeated injection of aldosterone induced hyponatremia and moderate hyperkalemia (Holmes and Butler, 1%). Similarly in the eel, Anguillu anguillu, maintained in freshwater, cortisol in
high doses induced hyponatremia and increased muscle water content
while muscle sodium concentration declined. Aldosterone, given in smaller
doses, had no effect ( D. K. 0. Chan et al., 196%).
From the information derived from these injection studies, it is not
possible to conclude that adrenocorticosteroids have an obvious physiological role in the control of osmoregulation. In fact, these steroids often
produced deleterious effects in intact animals. Moreover, on the basis that
injection of adrenal steroids did not promote the adaptation of stenohaline marine teleost fish to freshwater, it has been argued that adrenocorticosteroids had no role to play in osmoregulation in fish (Lockley,
1957; Edelman et al., 1960). It must be remembered that in general hormones do not initiate a physiological process, but they may take a vital
part in the control of the efficiency or speed of such a process when it has
been initiated. Many studies have employed doses of steroids of large
magnitude, and under normal conditions, the hormone is present in the
plasma in microgram amounts. The rate of secretion of steroid hormone
has been variously estimated to be about 2050 fig/lOO g body weight per
day. Exogenous hormones, especially those that do not naturally occur in
the animal, may produce spurious effects or may directly inhibit the action
of the naturally occurring equivalent hormone. A more informative experimental approach would be to test the hormones in animals without
endogenous secretions. This can be done either by surgical adrenalectomy or by pharmacological inhibition of the adrenal cortex with drugs.
Surgical adrenalectomy has been accomplished in a few species of
elasmobranchs. Hartman et al. (1944) found no significant changes in
plasma composition after removal of the adrenal cortex from the skate,
although Chester Jones (1957) recalculated their data to indicate at least
an elevation of plasma potassium concentration. More recently, Idler and
Szeplaki (1968) have in many ways confirmed the earlier work, in that
sodium, potassium, magnesium, and urea plasma levels were unchanged.
They found, however, an increase in plasma calcium concentration.
In teleost fish, owing to the special anatomical arrangement of the
adrenocortical tissue in the head kidney and cardinal veins, surgical
adrenalectomy has proved difficult. To date, this operation has been successful only in two species, namely, the goldfish (Etoh and Egami, 1963)
and the eel (Chester Jones et al., 1964). The latter species is euryhaline