such a principle in chondrichthyean fish is confused. Reports on the effects of hypophysectomy on the interrenals conflict (see HOAR, 1966). Mammalian corticotrophin fails to stimulate corticosteroid production of chondrichthyean interrenal tissues in vitro (BERN, DERoos, and BIGLIERI, 1962) but this could reflect
the limitations of such a system, or differences in the chemical structure of the mammalian and chondrichthyean hormones. Corticotrophin-like activity has been
directly demonstrated in the pituitary of a chondrichthyean fish (DERoos and
DERoos, 1964). The fishes thus usually appear to possess a corticotrophin-like hormone(s) that influences the activity of the interrenals.
In 1942 FRIEDMAN et al. demonstrated the presence of renin in the kidneys
of a number of freshwater teleost fish, though it was rather int erestin g that it was
not then found in marine species . At that time the existence of a renin-angiotensin
system for controlling interrenal secretion, as in mammals, was unknown. In the
latter group renin is principally concerned with the regulation of aldosterone,
though to a lesser extent it can also influence corticosterone secretion. Fish do not
seem to possess aldosterone but corticosterone is prominent. The kidneys (and corpuscles of STANNIUS in eels) of a variety of marine as well as freshwater teleost fish
have since been shown to contain a renin-like material (CHESTER JONES et al., 1966;
MIZOGAMI et aI., 1969, CAPELLI et al., 1970). The renin-activity is generally higher
in freshwater than in marine species and the levels increase two-fold when Japanese
eels and toadfish are adapted to life in fresh water (SOKABE et al., 1966; CAPELLI
et aI., 1970). The latter changes would be consistent with a role in sodium conservation as seen in mammals. Attempts to identify renin in the kidneys of elasmobranchs (4 species) and cyclostomes (2 species) have not been successful (NISHIMURA et al., 1970) so that such a mechanism may not be present in all of the fishes .
c) Adenohypophysis - Prolactin
The adenohypophysis of fishes contains a product which is homologous w ith mammalian prolactin. Its precise actions and properties differ somewhat from the tetrapod secretion, but in a manner that may be expected to result from differences
in their amino acid constitution. 'Prolactin' from a variety of vertebrates can initiate
the pre-breeding 'water drive' in the efts of certain newts (see page 186) and this
includes most groups of fishes (GRANT and PICKFORD, 1959). The eft 'w ater drive'
response is quite specific to this type of secretion and has provided a very useful
biological method for detecting the presence of such substances. There are also
some additional methods for characterizing 'prolactins' that are based on their effects in other vertebrates. In mammals prolactin promotes the growth and secretion
of the mammary glands, while in columbiform birds, such as doves and pigeons,
it initiates hypertrophy and secretion of the crop-sac glands . These three responses
have been particularly useful tests in comparing the properties of the prolactin secretions from different groups of vertebrates (see BERN and NICOLL, 1968). Prolactin can also initiate a variety of other responses in different vertebrate preparations, and these include a luteotrophic action on the corpus luteum of rats and
increased growth in amphibian tadpoles. However, the most interesting effect related to our present subject is its ability to enhance the survival of certain hypophy208
the limitations of such a system, or differences in the chemical structure of the mammalian and chondrichthyean hormones. Corticotrophin-like activity has been
directly demonstrated in the pituitary of a chondrichthyean fish (DERoos and
DERoos, 1964). The fishes thus usually appear to possess a corticotrophin-like hormone(s) that influences the activity of the interrenals.
In 1942 FRIEDMAN et al. demonstrated the presence of renin in the kidneys
of a number of freshwater teleost fish, though it was rather int erestin g that it was
not then found in marine species . At that time the existence of a renin-angiotensin
system for controlling interrenal secretion, as in mammals, was unknown. In the
latter group renin is principally concerned with the regulation of aldosterone,
though to a lesser extent it can also influence corticosterone secretion. Fish do not
seem to possess aldosterone but corticosterone is prominent. The kidneys (and corpuscles of STANNIUS in eels) of a variety of marine as well as freshwater teleost fish
have since been shown to contain a renin-like material (CHESTER JONES et al., 1966;
MIZOGAMI et aI., 1969, CAPELLI et al., 1970). The renin-activity is generally higher
in freshwater than in marine species and the levels increase two-fold when Japanese
eels and toadfish are adapted to life in fresh water (SOKABE et al., 1966; CAPELLI
et aI., 1970). The latter changes would be consistent with a role in sodium conservation as seen in mammals. Attempts to identify renin in the kidneys of elasmobranchs (4 species) and cyclostomes (2 species) have not been successful (NISHIMURA et al., 1970) so that such a mechanism may not be present in all of the fishes .
c) Adenohypophysis - Prolactin
The adenohypophysis of fishes contains a product which is homologous w ith mammalian prolactin. Its precise actions and properties differ somewhat from the tetrapod secretion, but in a manner that may be expected to result from differences
in their amino acid constitution. 'Prolactin' from a variety of vertebrates can initiate
the pre-breeding 'water drive' in the efts of certain newts (see page 186) and this
includes most groups of fishes (GRANT and PICKFORD, 1959). The eft 'w ater drive'
response is quite specific to this type of secretion and has provided a very useful
biological method for detecting the presence of such substances. There are also
some additional methods for characterizing 'prolactins' that are based on their effects in other vertebrates. In mammals prolactin promotes the growth and secretion
of the mammary glands, while in columbiform birds, such as doves and pigeons,
it initiates hypertrophy and secretion of the crop-sac glands . These three responses
have been particularly useful tests in comparing the properties of the prolactin secretions from different groups of vertebrates (see BERN and NICOLL, 1968). Prolactin can also initiate a variety of other responses in different vertebrate preparations, and these include a luteotrophic action on the corpus luteum of rats and
increased growth in amphibian tadpoles. However, the most interesting effect related to our present subject is its ability to enhance the survival of certain hypophy208