6. ADRENAL STEROIDS AND ACTH
337
isotonic with plasma (D. K. 0. Chan et al., 1967b; Mayer et al., 1967).
Among those that survive, there was a marked decline in body weight
associated with dehydration ( Fig. 2 ) . Plasma sodium, potassium, calcium,
magnesium, and chloride concentrations rose to very high levels (Table
11). There was a decline in muscle water content while muscle sodium
and magnesium content increased (D. K. 0. Chan et al., 196713; Fig. 3).
The normal mechanisms whereby the euryhaline eel maintains water
and electrolyte homeostasis have been impaired in the absence of the
adrenal cortex. In teleost fish the gills, the kidney, and the gut are the
principal sites of water and electrolyte exchange between the body fluids
and the external environment. The role of the adrenocortical secretions
in the control of the functional capacity of each of these systems will now
be considered.
1. THE GILLS
High doses of exogenous corticosteroid often produce deleterious effects upon the electrolyte transporting function of the gills. In freshwater
goldfish, Carassius aurutus, DOC depressed sodium influx across the gills,
but it had no effect upon sodium efflux, while cortisone had little or no
effect even when the animal was given a hypertonic sodium load (Sexton,
1955). The trout, Salmo gairdneri, similarly loaded, exhibited increased
extrarenal (presumably branchial) sodium efflux as a result of cortisol and
DOC injections. Deoxycorticosterone also depressed the sodium influx
in these trout (Chester Jones et al., 1959; Holmes, 1959). In the eel,
Anguilh anguilh, maintained in freshwater, milligram injections of cortisol increased the net sodium loss across the gills (Chester Jones et al,,
1967; Henderson and Chester Jones, 1967; D. K. 0. Chan et al., 1969).
However, if the dose of cortisol is reduced to a calculated “physiological”
level (i.e., within the secretory capacity of the adrenal cortex under normal in vivo conditions) the net uptake of sodium from the environmental
water can be enhanced. This has been shown for both the intact and
adrenalectomized eel (D. K. 0. Chan et aZ., 1969).
Aldosterone may inhibit or stimulate net sodium uptake in intact
freshwater eels but enhance it in adrenalectomized fish (Chester Jones
et al., 1962; Henderson and Chester Jones, 1967; Table 111). In the seawater eel, aldosterone has been shown to stimulate the sodium efflux
across the gills ( Mayer and Maetz, 1967).
Although the mechanism of action of aldosterone in amphibians and
mammals has been partially defined (Sharp and Leaf, 1966; Edelman,
1966), that of cortisol on the gills of teleosts is largely unexplored. In the
eel the functional capacity of the sodium pump residing in the branchial
337
isotonic with plasma (D. K. 0. Chan et al., 1967b; Mayer et al., 1967).
Among those that survive, there was a marked decline in body weight
associated with dehydration ( Fig. 2 ) . Plasma sodium, potassium, calcium,
magnesium, and chloride concentrations rose to very high levels (Table
11). There was a decline in muscle water content while muscle sodium
and magnesium content increased (D. K. 0. Chan et al., 196713; Fig. 3).
The normal mechanisms whereby the euryhaline eel maintains water
and electrolyte homeostasis have been impaired in the absence of the
adrenal cortex. In teleost fish the gills, the kidney, and the gut are the
principal sites of water and electrolyte exchange between the body fluids
and the external environment. The role of the adrenocortical secretions
in the control of the functional capacity of each of these systems will now
be considered.
1. THE GILLS
High doses of exogenous corticosteroid often produce deleterious effects upon the electrolyte transporting function of the gills. In freshwater
goldfish, Carassius aurutus, DOC depressed sodium influx across the gills,
but it had no effect upon sodium efflux, while cortisone had little or no
effect even when the animal was given a hypertonic sodium load (Sexton,
1955). The trout, Salmo gairdneri, similarly loaded, exhibited increased
extrarenal (presumably branchial) sodium efflux as a result of cortisol and
DOC injections. Deoxycorticosterone also depressed the sodium influx
in these trout (Chester Jones et al., 1959; Holmes, 1959). In the eel,
Anguilh anguilh, maintained in freshwater, milligram injections of cortisol increased the net sodium loss across the gills (Chester Jones et al,,
1967; Henderson and Chester Jones, 1967; D. K. 0. Chan et al., 1969).
However, if the dose of cortisol is reduced to a calculated “physiological”
level (i.e., within the secretory capacity of the adrenal cortex under normal in vivo conditions) the net uptake of sodium from the environmental
water can be enhanced. This has been shown for both the intact and
adrenalectomized eel (D. K. 0. Chan et aZ., 1969).
Aldosterone may inhibit or stimulate net sodium uptake in intact
freshwater eels but enhance it in adrenalectomized fish (Chester Jones
et al., 1962; Henderson and Chester Jones, 1967; Table 111). In the seawater eel, aldosterone has been shown to stimulate the sodium efflux
across the gills ( Mayer and Maetz, 1967).
Although the mechanism of action of aldosterone in amphibians and
mammals has been partially defined (Sharp and Leaf, 1966; Edelman,
1966), that of cortisol on the gills of teleosts is largely unexplored. In the
eel the functional capacity of the sodium pump residing in the branchial