site of corticosteroid action thus remains somewhat enigmatic in the Amphibia.
N evertheless, there remain three extrarenal sites where th ese stero ids can act: the
skin, the urinary bladder and the colon. Cutaneous losses of sodium chlo ride have
been shown to inc rease in hypophysectomized fro gs, Rana temporaria and R .
pipiens (JORGENSEN, 1947; MYERS, FLEMING, and SCHEER, 1956). This is due to
an accelerated outflux (' leakage') of sodium while th e active transport mechanism
per se appears to be littl e affected . It is interesting th at the skin of R. pipiens also
become s more perm eable to water following hypophyse ctomy (LEVINSKYand SAWYER , 1952). MIDDLER et al. were able partially to maintain hypophysectomized
Bufo m arin us with injections of cort isol or cort icosteron e, but aldo sterone w as
completeley ineffective. The available evidence suggests that the excessive sodium
loss experienced by hyp ophysectomized amphibian s is du e pr edominantly to a deficien cy of ' glucocorticoids ' (cort icosterone) rather th an th e absence of a 'mineralocorticoid'. A combination of th e two is pr obably optimal for maintaining such
animals. This is well known to be the case in mammals which cannot be maintained
during adrenal insufficiency by aldosterone alone , wh ereas cortisol is adequate.
Corticosterone is usually considered to be a glucocort icoid but it also exert s
mineralocorticoid effects in amphibians; it can , for instance, stimulate sodium
tran sport across th e toad urinary bladder (HANDLER et aI., 1969 ).
Little is known about the ph ysiology of adrenocortical tissues in urodeles. H ypophysectomized newts , Triturus cristatus, suffer an excessive loss of both sodium
and pota ssium (PEYROT et al., 1963). Th e injecti on of aldos ter one or cort isol into
these newts results in a retention of sodium and a loss of potassium by the muscl es
(FERRERI et al., 1967). When both of the se steroids were given to gether th eir effects
were greatly enhanced. Aldosterone, when injected into Nectu rus m aculosus, increased sod ium transport across their urinary bladd er in v itro (BENTLEY, 1971 a).
The adrenocorti cal ph ysiolo gy of thi s inte resting group of amphibians deserves
much mo re attenti on.
The homolo gou s corticosteroids of amphibians are doubtless involved in the
regulation of electrolyt es. The osmoregulat ion of th e Amphibia is somewhat complicated compared to other tetrapods, as the ir skin provides a prominent pathway
through which salts may travel in either direction. Such transfers may take place
by passive diffus ion or be influenced by metabolically controlled active transport
processes. The int egrity of thi s barrier is vital to osmo tic equilibr ium, especi ally
in an aquatic environment. In other tetrapods renal processes are the principal determinant of salt cons ervation, but in the Amphibia th e skin and urinary bladder
are also invol ved. C orticosteroids affect the osmoregulation in amphibians in three
main ways. Fir stly, the y influence the no rmal metabolic processes in th e bod y
(glucocort icoid action ) and so pr obably playa ro le in maintaining the int egrity of
the skin to th e passive transfers of molecules. Thus in th e absence of such hormon es
th e skin may becom e mor e ' leaky' resulting in a steady loss of solute. Secondly,
th ey may playa role in providing suitable metabolic 'fuel' for the pro cesses of active
transport of ions , also a glucocorticoid effect. Thirdl y, a mineralocorticoid effect
(principally du e to aldosteron e?) may be mor e directly involved in cont ro lling th e
day-t o-day activity of th e sodi um ' pumps'. The sites of action of aldo steron e in
amphibians differ fro m th ose in mamm als for w hile it has been shown un equ ivocally to increase sodium tr ansport across th e skin and urinary bladd er , th ere is littl e
191
N evertheless, there remain three extrarenal sites where th ese stero ids can act: the
skin, the urinary bladder and the colon. Cutaneous losses of sodium chlo ride have
been shown to inc rease in hypophysectomized fro gs, Rana temporaria and R .
pipiens (JORGENSEN, 1947; MYERS, FLEMING, and SCHEER, 1956). This is due to
an accelerated outflux (' leakage') of sodium while th e active transport mechanism
per se appears to be littl e affected . It is interesting th at the skin of R. pipiens also
become s more perm eable to water following hypophyse ctomy (LEVINSKYand SAWYER , 1952). MIDDLER et al. were able partially to maintain hypophysectomized
Bufo m arin us with injections of cort isol or cort icosteron e, but aldo sterone w as
completeley ineffective. The available evidence suggests that the excessive sodium
loss experienced by hyp ophysectomized amphibian s is du e pr edominantly to a deficien cy of ' glucocorticoids ' (cort icosterone) rather th an th e absence of a 'mineralocorticoid'. A combination of th e two is pr obably optimal for maintaining such
animals. This is well known to be the case in mammals which cannot be maintained
during adrenal insufficiency by aldosterone alone , wh ereas cortisol is adequate.
Corticosterone is usually considered to be a glucocort icoid but it also exert s
mineralocorticoid effects in amphibians; it can , for instance, stimulate sodium
tran sport across th e toad urinary bladder (HANDLER et aI., 1969 ).
Little is known about the ph ysiology of adrenocortical tissues in urodeles. H ypophysectomized newts , Triturus cristatus, suffer an excessive loss of both sodium
and pota ssium (PEYROT et al., 1963). Th e injecti on of aldos ter one or cort isol into
these newts results in a retention of sodium and a loss of potassium by the muscl es
(FERRERI et al., 1967). When both of the se steroids were given to gether th eir effects
were greatly enhanced. Aldosterone, when injected into Nectu rus m aculosus, increased sod ium transport across their urinary bladd er in v itro (BENTLEY, 1971 a).
The adrenocorti cal ph ysiolo gy of thi s inte resting group of amphibians deserves
much mo re attenti on.
The homolo gou s corticosteroids of amphibians are doubtless involved in the
regulation of electrolyt es. The osmoregulat ion of th e Amphibia is somewhat complicated compared to other tetrapods, as the ir skin provides a prominent pathway
through which salts may travel in either direction. Such transfers may take place
by passive diffus ion or be influenced by metabolically controlled active transport
processes. The int egrity of thi s barrier is vital to osmo tic equilibr ium, especi ally
in an aquatic environment. In other tetrapods renal processes are the principal determinant of salt cons ervation, but in the Amphibia th e skin and urinary bladder
are also invol ved. C orticosteroids affect the osmoregulation in amphibians in three
main ways. Fir stly, the y influence the no rmal metabolic processes in th e bod y
(glucocort icoid action ) and so pr obably playa ro le in maintaining the int egrity of
the skin to th e passive transfers of molecules. Thus in th e absence of such hormon es
th e skin may becom e mor e ' leaky' resulting in a steady loss of solute. Secondly,
th ey may playa role in providing suitable metabolic 'fuel' for the pro cesses of active
transport of ions , also a glucocorticoid effect. Thirdl y, a mineralocorticoid effect
(principally du e to aldosteron e?) may be mor e directly involved in cont ro lling th e
day-t o-day activity of th e sodi um ' pumps'. The sites of action of aldo steron e in
amphibians differ fro m th ose in mamm als for w hile it has been shown un equ ivocally to increase sodium tr ansport across th e skin and urinary bladd er , th ere is littl e
191