BUTLER et al., 1969). As judged by th e marked declin e in circulating co rt isol levels
in eels, th is op eration removes mo st of th e int errenal tissu e (BUTLER et al., 1969).
Interrenale ctorny result s in a decline of th e plasm a sodium levels in European and
N o rt h American eels, Anguilla rostrata, kept in fres h water. There were no co nsiste nt changes in th e potassium co ncentrations (CHAN et al., 1967 a; BUTLER et
al., 1969). MAETz (1969 a) measur ed th e influx and ou tflux of sodium in European
eels and found th at when th ey were in fr esh water the infl ux of sodium acro ss the
gills declin ed follo w ing inte rrenalecto my. Th e decreased plasma sodium co ncent ration ob served in th ese freshwa ter eels is due to th e failu re of th e gills to absorb
adequ ate sodium fro m th e externa l media, but thi s can be restor ed by th e injec tion
of aldost erone o r sma ll doses of co rt isol (HENDERSON and CH ESTER] ONES, 1967).
BUTLER et al. also not ed pr ofound changes in th e carbo hy d rate metabolism of such
eels ind icating that co rticostero ids , as in mammals, are also involved in th e control
of gene ral metaboli sm. It is inte resting that lar ger doses of cortisol enhance th e
loss of sodium from th e gills. Thus, MAYER et al. (1967) found th at int errenalecto my
in sea-water eels resulted in an accumulation of sodium in th e body, but th e injection of cortisol co uld restore this to norm al. The rate of the turnover of th e
sodium follo wing int errenalectomy in eels kept in sea-water is reduced in each hour
from 33% to onl y 60/0 of the to tal pr esent in th e body (MAETZ, 1969 a). This can
also be restored by injecting co rt isol. Cortisol thus appears to be able to stim ulate
active sodium tran sport in eels whether it is occ ur ring fro m the external solut ion
into th e fish, o r from th e fish into th e surrounding sea-water.
H ypophysectomy clearly disturbs th e so dium m etabolism of fish in fresh water
th ou gh the y do perf ectl y well in sea-w ater. In fr esh wa ter th is extirpatio n is fatal
to some, such as Fundulus beteroclitus, Poecilia latipinna and Tilapia m ossambica
and results in a dep letion of th e body sodi um in o thers, like Carassius aura tus, Fundulus k ansae and A nguilla anguilla (T able 7.11). Th is is du e to an excessive leakage
(ou tflux) of sodium across th e gills of Fundulus heteroclitus, th e eel and th e goldfish, while in F. kan sae urinary losses are inc reased . In all fish, except the latt er,
th e outflux can be reduced by the injection of mamm alian prolactin . Another
ade nohypo physi al hormon e suspected of influencing th e osmoregulation of fish
is co rti co trophin, which acts by initi atin g release of co rt icosteroids from the interr enals. Co rticotroph in, ho wever, doe s not generally have a dram atic effect on
the sod ium metabolism of hypophysectomized fr eshwa ter fish. Nevertheless it is
effective in hypophysectomized eels, where, in co njunction with prolactin, it resto res the osmotic balance (CHAN et al., 1968; MAETZ, MAYER, and CHARTIERBARADUC, 1967a). T et rap od ad ren ocortical tissue s are not co mpletely controlled
by corticotrophin, and if th is is also so in fishe s (if a renin-angiot ensin system is
pr esent) sufficient corticosteroids may still be available to meet th eir need s follo wing hypoph ysectom y. P rol actin reduces th e br anchi al o utflux of sodium in most
hyp ophysectomized fish and th is would app ear to be its principal site of action.
Int err en alectomized eels cann ot take up adequate sodium through th eir gills, but
thi s can be facilitated by th e injection of corticotrophin or co rt isol. Therefore, co rticos tero ids pr obably act in fresh wat er fish to facilit ate bran chial influx of so dium,
th e simultaneous actio n of these steroids and prol actin at th is site regul atin g th e
sodium conte nt of the fish.
The precise ro le and metabolic site of action of prolactin and corticosteroids d ur241
in eels, th is op eration removes mo st of th e int errenal tissu e (BUTLER et al., 1969).
Interrenale ctorny result s in a decline of th e plasm a sodium levels in European and
N o rt h American eels, Anguilla rostrata, kept in fres h water. There were no co nsiste nt changes in th e potassium co ncentrations (CHAN et al., 1967 a; BUTLER et
al., 1969). MAETz (1969 a) measur ed th e influx and ou tflux of sodium in European
eels and found th at when th ey were in fr esh water the infl ux of sodium acro ss the
gills declin ed follo w ing inte rrenalecto my. Th e decreased plasma sodium co ncent ration ob served in th ese freshwa ter eels is due to th e failu re of th e gills to absorb
adequ ate sodium fro m th e externa l media, but thi s can be restor ed by th e injec tion
of aldost erone o r sma ll doses of co rt isol (HENDERSON and CH ESTER] ONES, 1967).
BUTLER et al. also not ed pr ofound changes in th e carbo hy d rate metabolism of such
eels ind icating that co rticostero ids , as in mammals, are also involved in th e control
of gene ral metaboli sm. It is inte resting that lar ger doses of cortisol enhance th e
loss of sodium from th e gills. Thus, MAYER et al. (1967) found th at int errenalecto my
in sea-water eels resulted in an accumulation of sodium in th e body, but th e injection of cortisol co uld restore this to norm al. The rate of the turnover of th e
sodium follo wing int errenalectomy in eels kept in sea-water is reduced in each hour
from 33% to onl y 60/0 of the to tal pr esent in th e body (MAETZ, 1969 a). This can
also be restored by injecting co rt isol. Cortisol thus appears to be able to stim ulate
active sodium tran sport in eels whether it is occ ur ring fro m the external solut ion
into th e fish, o r from th e fish into th e surrounding sea-water.
H ypophysectomy clearly disturbs th e so dium m etabolism of fish in fresh water
th ou gh the y do perf ectl y well in sea-w ater. In fr esh wa ter th is extirpatio n is fatal
to some, such as Fundulus beteroclitus, Poecilia latipinna and Tilapia m ossambica
and results in a dep letion of th e body sodi um in o thers, like Carassius aura tus, Fundulus k ansae and A nguilla anguilla (T able 7.11). Th is is du e to an excessive leakage
(ou tflux) of sodium across th e gills of Fundulus heteroclitus, th e eel and th e goldfish, while in F. kan sae urinary losses are inc reased . In all fish, except the latt er,
th e outflux can be reduced by the injection of mamm alian prolactin . Another
ade nohypo physi al hormon e suspected of influencing th e osmoregulation of fish
is co rti co trophin, which acts by initi atin g release of co rt icosteroids from the interr enals. Co rticotroph in, ho wever, doe s not generally have a dram atic effect on
the sod ium metabolism of hypophysectomized fr eshwa ter fish. Nevertheless it is
effective in hypophysectomized eels, where, in co njunction with prolactin, it resto res the osmotic balance (CHAN et al., 1968; MAETZ, MAYER, and CHARTIERBARADUC, 1967a). T et rap od ad ren ocortical tissue s are not co mpletely controlled
by corticotrophin, and if th is is also so in fishe s (if a renin-angiot ensin system is
pr esent) sufficient corticosteroids may still be available to meet th eir need s follo wing hypoph ysectom y. P rol actin reduces th e br anchi al o utflux of sodium in most
hyp ophysectomized fish and th is would app ear to be its principal site of action.
Int err en alectomized eels cann ot take up adequate sodium through th eir gills, but
thi s can be facilitated by th e injection of corticotrophin or co rt isol. Therefore, co rticos tero ids pr obably act in fresh wat er fish to facilit ate bran chial influx of so dium,
th e simultaneous actio n of these steroids and prol actin at th is site regul atin g th e
sodium conte nt of the fish.
The precise ro le and metabolic site of action of prolactin and corticosteroids d ur241