et al. (1961) suggest that there is also a considerable reduction in sodium transport.
The ability to 'turn off' such cutaneous processes may be as important as 'turning
(them) on' so that hormonal control could conceivably play an important role in
such species. At present there is no information about this.
P) Neurohypophysial Peptides. Neurohypophysial peptides not only increase the
permeability of the anuran skin to water but also promote active sodium transport.
This also occurs in some urodeles. FUHRMAN and USSING (1951) showed that
mammalian neurohypophysial pep tides increase sodium transport across frog skin
and vasotocin has since been shown to be even more effective, being effective at
concentrations as low as lO-lOM (JARD et aI., 1960; MAETZ, 1963). This action on
sodium transport ('natriferic effect') has been demonstrated in a number of anurans
including Rana esculenta, R . catesbeiana, Bulo bulo, B. marinus and Xenopus laevis
(MAETZ, 1963; BENTLEY, 1969 b). The isolated skin of the urodeles Triturus alpestris
and T. cristatus (BENTLEY and HELLER, 1964) and Ambystoma mexicanus (ACEVES,
ERLIJ,and EDWARDS, 1968) also respond in this manner. I have been unable to show
such an effect in Ambystoma tigrinum, in vitro, but the results of ALVARADO and
JOHNSON (1965) suggest that it occurs in vivo. The increased transport of sodium
and water in response to neurohypophysial peptides does not represent a single general action of such peptides on the membrane; the two processes, water and sodium transfer, are quite distinct. This is indicated by several observations. Thus
BOURGUET and MAETZ (1961) showed that the relative activities of different neurohypophysial peptides on water and sodium transfer are not parallel. In addition,
some amphibians like Triturus alpestris and Xenopus laeuis, exhibit the natriieric
but not the hydrosmotic (water) response. Whether the natriferic effect of such
peptides respresents a significant osmoregulatory response is uncertain. However,
it should be remembered that this action of neurohypophysial peptides is less susstained than that of the corticosteroids, and that frogs and toads placed in salt solutions release large amounts of vasotocin into the circulation. The latter does not
make homeostatic sense with respect to sodium regulation. In the Amphibia the
natriferic effect of vasotocin is probably not osmoregulatory in its nature though
it may conceivably have a more localized function, or even reflect some osmotic
significance in the ancestors of this group.
Other hormones have also been reported to increase sodium transport across
the amphibian skin . Adrenaline has this effect in Rana esculenta; this action is probably mediated by production of cyclic AMP, which is also a metabolic intermediate
in the action of neurohypophysial peptides (BASTIDE and JARD, 1968). Adrenaline
promotes loss of chloride from the frog skin by stimulating the secretion of skin
-glands (USSING, 1960). Thyroid hormones have also been reported to increase
sodium transport across the skin of Bufo bulo (GREEN and MATTY, 1963) but others
(TAYLOR and BARKER, 1967) have been unable to confirm this. The skin of Bulo
marinus exhibits an increased active sodium transport when it is exposed to insulin
and if this acts in conjunction with aldosterone, sodium transport is considerably
higher than if each is present alone (ANDRE and CRABBE, 1966). Thus optimal rates
of sodium transport in vivo may be the result of an interactionof several hormones.
181
The ability to 'turn off' such cutaneous processes may be as important as 'turning
(them) on' so that hormonal control could conceivably play an important role in
such species. At present there is no information about this.
P) Neurohypophysial Peptides. Neurohypophysial peptides not only increase the
permeability of the anuran skin to water but also promote active sodium transport.
This also occurs in some urodeles. FUHRMAN and USSING (1951) showed that
mammalian neurohypophysial pep tides increase sodium transport across frog skin
and vasotocin has since been shown to be even more effective, being effective at
concentrations as low as lO-lOM (JARD et aI., 1960; MAETZ, 1963). This action on
sodium transport ('natriferic effect') has been demonstrated in a number of anurans
including Rana esculenta, R . catesbeiana, Bulo bulo, B. marinus and Xenopus laevis
(MAETZ, 1963; BENTLEY, 1969 b). The isolated skin of the urodeles Triturus alpestris
and T. cristatus (BENTLEY and HELLER, 1964) and Ambystoma mexicanus (ACEVES,
ERLIJ,and EDWARDS, 1968) also respond in this manner. I have been unable to show
such an effect in Ambystoma tigrinum, in vitro, but the results of ALVARADO and
JOHNSON (1965) suggest that it occurs in vivo. The increased transport of sodium
and water in response to neurohypophysial peptides does not represent a single general action of such peptides on the membrane; the two processes, water and sodium transfer, are quite distinct. This is indicated by several observations. Thus
BOURGUET and MAETZ (1961) showed that the relative activities of different neurohypophysial peptides on water and sodium transfer are not parallel. In addition,
some amphibians like Triturus alpestris and Xenopus laeuis, exhibit the natriieric
but not the hydrosmotic (water) response. Whether the natriferic effect of such
peptides respresents a significant osmoregulatory response is uncertain. However,
it should be remembered that this action of neurohypophysial peptides is less susstained than that of the corticosteroids, and that frogs and toads placed in salt solutions release large amounts of vasotocin into the circulation. The latter does not
make homeostatic sense with respect to sodium regulation. In the Amphibia the
natriferic effect of vasotocin is probably not osmoregulatory in its nature though
it may conceivably have a more localized function, or even reflect some osmotic
significance in the ancestors of this group.
Other hormones have also been reported to increase sodium transport across
the amphibian skin . Adrenaline has this effect in Rana esculenta; this action is probably mediated by production of cyclic AMP, which is also a metabolic intermediate
in the action of neurohypophysial peptides (BASTIDE and JARD, 1968). Adrenaline
promotes loss of chloride from the frog skin by stimulating the secretion of skin
-glands (USSING, 1960). Thyroid hormones have also been reported to increase
sodium transport across the skin of Bufo bulo (GREEN and MATTY, 1963) but others
(TAYLOR and BARKER, 1967) have been unable to confirm this. The skin of Bulo
marinus exhibits an increased active sodium transport when it is exposed to insulin
and if this acts in conjunction with aldosterone, sodium transport is considerably
higher than if each is present alone (ANDRE and CRABBE, 1966). Thus optimal rates
of sodium transport in vivo may be the result of an interactionof several hormones.
181