6. ADRENAL STEROIDS AND ACTH
341
1967), possibly suggesting that exogenous steroids inhibit actions of
endogenous hormones. In the seawater-adapted animal, adrenalectomy
drastically reduced sodium efflux across the gills (Table IV; Fig. 6 ) ,
which can be reversed with a small dose of cortisol (Mayer et al., 1967).
However, in contrast to the reports for aldosterone action in frog skin
and toad bladder, actinomycin did not prevent the stimulatory effect of
cortisol on the g d s of seawater eels ( Maetz, 1968).
2. THE KIDNEY
The freshwater eel produces a copious urine amounting to about 26
ml/kg body weight per 2.4 hr at 12°C. Following adrenalectomy, there
was a gradual reduction in urine production with concomitant reduction
in inulin clearance rates. The effect became discernible about 4 days after
the surgery. Urine volume was reduced to about 13 ml/kg/day and was
sustained at this level for at least 2 weeks, the maximum time of observation. Urinary electrolyte concentrations showed a tendency to rise so
that total urinary electrolyte excretion was normal or slightly elevated
(Table V; Fig. 7). Compared with sham-operated controls, the reduction
in urine volume was sufficient to account for the degree of water retention
in the animal.
A series of steroids given at 20 pg/lOO glday was tested in the
adrenalectomized eel. Cortisol maintained normal renal function in this
preparation. ll-Deoxycortisol was less active while aldosterone and deoxycorticosterone were without effect (Fig. 7; D. K. 0. Chan et al., 1969).
Thus the kidney of the eel is dependent on an adrenocortical hormone
for normal function. It is interesting that aldosterone, not so far found in
the eel, had no effect on urinary sodium in this species. In the intact
freshwater trout injection of corticosterone, cortisol being the predominant steroid, reduced inulin clearance (Holmes and McBean, 1963).
Whether this is because of inhibition of endogenous hormone action
remains to be examined.
3. THE GASTROINTESTINAL TRACT
The relevance of the gastrointestinal system to salt/water balance, particularly in marine teleosts is well recognized. Early experiments (H. W.
Smith, 1930; Keys, 1933) established that the osmotic gradient existing
between marine teleosts and their environment is conducive to passive
outflux of water across permeable surfaces. This outflux is offset by ingestion of the environmental water followed by isotonic absorption and then
renal and extrarenal excretion of the obligatorily gained ions.
The actual rate at which seawater is ingested varies considerably from
341
1967), possibly suggesting that exogenous steroids inhibit actions of
endogenous hormones. In the seawater-adapted animal, adrenalectomy
drastically reduced sodium efflux across the gills (Table IV; Fig. 6 ) ,
which can be reversed with a small dose of cortisol (Mayer et al., 1967).
However, in contrast to the reports for aldosterone action in frog skin
and toad bladder, actinomycin did not prevent the stimulatory effect of
cortisol on the g d s of seawater eels ( Maetz, 1968).
2. THE KIDNEY
The freshwater eel produces a copious urine amounting to about 26
ml/kg body weight per 2.4 hr at 12°C. Following adrenalectomy, there
was a gradual reduction in urine production with concomitant reduction
in inulin clearance rates. The effect became discernible about 4 days after
the surgery. Urine volume was reduced to about 13 ml/kg/day and was
sustained at this level for at least 2 weeks, the maximum time of observation. Urinary electrolyte concentrations showed a tendency to rise so
that total urinary electrolyte excretion was normal or slightly elevated
(Table V; Fig. 7). Compared with sham-operated controls, the reduction
in urine volume was sufficient to account for the degree of water retention
in the animal.
A series of steroids given at 20 pg/lOO glday was tested in the
adrenalectomized eel. Cortisol maintained normal renal function in this
preparation. ll-Deoxycortisol was less active while aldosterone and deoxycorticosterone were without effect (Fig. 7; D. K. 0. Chan et al., 1969).
Thus the kidney of the eel is dependent on an adrenocortical hormone
for normal function. It is interesting that aldosterone, not so far found in
the eel, had no effect on urinary sodium in this species. In the intact
freshwater trout injection of corticosterone, cortisol being the predominant steroid, reduced inulin clearance (Holmes and McBean, 1963).
Whether this is because of inhibition of endogenous hormone action
remains to be examined.
3. THE GASTROINTESTINAL TRACT
The relevance of the gastrointestinal system to salt/water balance, particularly in marine teleosts is well recognized. Early experiments (H. W.
Smith, 1930; Keys, 1933) established that the osmotic gradient existing
between marine teleosts and their environment is conducive to passive
outflux of water across permeable surfaces. This outflux is offset by ingestion of the environmental water followed by isotonic absorption and then
renal and extrarenal excretion of the obligatorily gained ions.
The actual rate at which seawater is ingested varies considerably from