into the plasma. Sodium can be actively transported across the intestine of fish
(HOUSE and GREEN, 1963) and this presumably accounts for the absorption of a
large additional amount of salt, which takes water with it across to the plasma (see
also SKADHAUGE, 1969 b). SKADHAUGE and MAETZ (1967) devised an ingenious system for following the absorption of water and salt across the eel in testine in vivo,
The gut of these fish was cannulated at both ends and a sol urion was slowly circulated through it. From the changes of phenol red and 24Na in this fluid the process
of its absorption could be seen. For the first 90 min following the admission of
the sea-water into the gut, fluid moved into the lumen, but after this period absorption into the body fluids took place. There was a continual transport of sodium
from the gut, the water absorption being coupled to this . No fluid transfer could
be seen if a non-absorbable solute such as mannitol was used to replace the salts
in the sea-water.
The rate of absorption of water from a salt solution perfused into the gut is
greater in fish that are adapted to sea-water than those in fresh water. This has been
observed in eels both in vitro (SHARRAH et al., 1964 b; OIDE and UTIDA, 1967)
and in vivo (SKADHAUGE and MAETZ, 1967; SKADHAUGE, 1969 b): The latter investigators found that the rate of fluid absorption from dilute sea-water solutions
by the intestine perfused in vivo was 350 f/1I1 00 g h in eels adapted to fresh water,
compared with 1100 f/1I100 g h in eels kept in sea-water. The absorption of water
also appears to occur more efficiently in sea-water eels, as nearly twice the quantity
is moved for each mole of sodium transferred. This change in the ability to reabsorb
fluid from the gut takes place during a period of several days which follow placing
the eels in sea-water (OIDE and UTIDA, 1967). If the adenohypophysis is removed
from Japanese eels, Anguilla japonica, this adaptation in sea-water fails to appear,
but it can be promoted again by injections of corticotrophin or cortisol (HIRANO,
1967; HIRANO and UTIDA, 1968). Sodium transport across the isolated intestine
of these eels increases if the fish are pre-treated with cortisol (but not corticosterone), and this presumably partly accounts for the facilitated rate of fluid absorption. However, as observed by SKADHAUGE and MAETZ more water is also
transferred in relation to the sodium moved so that a direct increase in permeability
to water may also be involved.
The enzyme Na-K activated ATPase has been identified in the gut of the goldfish (M. SMITH, 1964; 1967) and of the Japanese eel (OIDE, 1967) and inhibition
by the drug ouabain blocks both the absorption of sodium and water. The activity
of this enzyme in the gut changes in different conditions, and is higher in eels
adapted to sea-water than in those in fresh water (OIDE, 1967). It is not clear if
this is related to the activity of pituitary or interrenal glands, but it is interesting
that increases in the level of this enzyme in the gills of the killifish do not occur
after hypophysectomy (EpSTEIN et al., 1967). It is possible that the pituitary-interrenal axis is concerned with inducing long-term changes in the activity of NaK activated ATPase but at present the evidence is inconclusive. However, cortisol
injections have recently been shown to restore the Na-K activated ATPase levels
in the intestine (as well as gills and kidneys) of hypophysectomized killifish kept
in sea-water (PICKFORD et al. 1970).
213
(HOUSE and GREEN, 1963) and this presumably accounts for the absorption of a
large additional amount of salt, which takes water with it across to the plasma (see
also SKADHAUGE, 1969 b). SKADHAUGE and MAETZ (1967) devised an ingenious system for following the absorption of water and salt across the eel in testine in vivo,
The gut of these fish was cannulated at both ends and a sol urion was slowly circulated through it. From the changes of phenol red and 24Na in this fluid the process
of its absorption could be seen. For the first 90 min following the admission of
the sea-water into the gut, fluid moved into the lumen, but after this period absorption into the body fluids took place. There was a continual transport of sodium
from the gut, the water absorption being coupled to this . No fluid transfer could
be seen if a non-absorbable solute such as mannitol was used to replace the salts
in the sea-water.
The rate of absorption of water from a salt solution perfused into the gut is
greater in fish that are adapted to sea-water than those in fresh water. This has been
observed in eels both in vitro (SHARRAH et al., 1964 b; OIDE and UTIDA, 1967)
and in vivo (SKADHAUGE and MAETZ, 1967; SKADHAUGE, 1969 b): The latter investigators found that the rate of fluid absorption from dilute sea-water solutions
by the intestine perfused in vivo was 350 f/1I1 00 g h in eels adapted to fresh water,
compared with 1100 f/1I100 g h in eels kept in sea-water. The absorption of water
also appears to occur more efficiently in sea-water eels, as nearly twice the quantity
is moved for each mole of sodium transferred. This change in the ability to reabsorb
fluid from the gut takes place during a period of several days which follow placing
the eels in sea-water (OIDE and UTIDA, 1967). If the adenohypophysis is removed
from Japanese eels, Anguilla japonica, this adaptation in sea-water fails to appear,
but it can be promoted again by injections of corticotrophin or cortisol (HIRANO,
1967; HIRANO and UTIDA, 1968). Sodium transport across the isolated intestine
of these eels increases if the fish are pre-treated with cortisol (but not corticosterone), and this presumably partly accounts for the facilitated rate of fluid absorption. However, as observed by SKADHAUGE and MAETZ more water is also
transferred in relation to the sodium moved so that a direct increase in permeability
to water may also be involved.
The enzyme Na-K activated ATPase has been identified in the gut of the goldfish (M. SMITH, 1964; 1967) and of the Japanese eel (OIDE, 1967) and inhibition
by the drug ouabain blocks both the absorption of sodium and water. The activity
of this enzyme in the gut changes in different conditions, and is higher in eels
adapted to sea-water than in those in fresh water (OIDE, 1967). It is not clear if
this is related to the activity of pituitary or interrenal glands, but it is interesting
that increases in the level of this enzyme in the gills of the killifish do not occur
after hypophysectomy (EpSTEIN et al., 1967). It is possible that the pituitary-interrenal axis is concerned with inducing long-term changes in the activity of NaK activated ATPase but at present the evidence is inconclusive. However, cortisol
injections have recently been shown to restore the Na-K activated ATPase levels
in the intestine (as well as gills and kidneys) of hypophysectomized killifish kept
in sea-water (PICKFORD et al. 1970).
213