The corpuscles of STANNIUS in the fishes have been shown to contain a vasopressor
material, which has been tentatively suggested as the equivalent of the latter control
system (CHESTER JONES et al., 1966) and this will be discussed in the next section.
9. Putative Endocrine Tissues in Fishes
The fishes have an evolutionary history that has been independent of tetrapods
for a long time . Phylerically and physiologically they are a very diverse group, with
a vast number of species. It would thus not be surprising to find endocrine tissues
amongst the fishes which have no homologues in the tetrapods, or even with other
piscine groups. Two such putative endocrine tissues are the corpuscles of STANNIUS
and the urophysis.
a) Corpuscles of STANNIUS
These islets of tissue are present in teleostean and holostean bony fishes, but are
apparently absent from other piscine groups. The corpuscles of STANNIUS vary in
number from two, in most teleosts, to forty or fifty in the holostean, Amia calva.
Embryologically they arise as evaginations of the pronephric duct and are situated
ventrally and posteriorly on the kidney, or they may lie caudally to this organ.
Since the original description of these corpuscles by STANNIUS in 1839, speculation about their function has been considerable. It has generally been thought
that they are endocrine glands, but this has yet to be established. RASQUIN (1956)
examined the histology of these tissues in the freshwater teleost, Astyanax rnexicanus, after it had been immersed in 1% sodium chloride solutions, or injected
with deoxycorticosterone. Cytological changes in the corpuscles that followed
such treatments suggested that they may be involved in osmoregulation. Ablation
of the corpuscles of STANNIUS in the eel results in a decreased plasma sodium level,
accompanied by an elevated concentration of potassium and calcium (LELoup-HATEY, 1964; M. FONTAINE, 1964). Such changes were ameliorated by the injection
of corpuscle tissue extracts. These results have been confirmed by CHAN et al.
(1967a), so that the evidence strongly supports the possibility of an osmoregulatory
role for these tissues.
The exact actions of the corpuscles of STANNIUS in osmotic regulation, and
the nature of their putative secretions are at present uncertain. Due probably to
the proximity of the STANNIUS corpuscles and the adrenocortical tissues in fishes,
the possibility that they are both parts of the same steroid secreting system has
been explored extensively. It should be noted, however, that the two groups of
tissues have distinct embryological origins and morphological sites, even though
they do both lie in the caudal regions of a fish. Many attempts have been made
to identify steroids in extracts of the corpuscles of STANNIUS, and to show formation and accumulation of such substances, after their in vitro incubation in the
presence or absence of steroid substrates. The results will be discussed in detail
in a later section, but they are variable and contradictory. There are some reports
of the presence of steroids (or steroid-like materials?) under certain conditions, but
78
material, which has been tentatively suggested as the equivalent of the latter control
system (CHESTER JONES et al., 1966) and this will be discussed in the next section.
9. Putative Endocrine Tissues in Fishes
The fishes have an evolutionary history that has been independent of tetrapods
for a long time . Phylerically and physiologically they are a very diverse group, with
a vast number of species. It would thus not be surprising to find endocrine tissues
amongst the fishes which have no homologues in the tetrapods, or even with other
piscine groups. Two such putative endocrine tissues are the corpuscles of STANNIUS
and the urophysis.
a) Corpuscles of STANNIUS
These islets of tissue are present in teleostean and holostean bony fishes, but are
apparently absent from other piscine groups. The corpuscles of STANNIUS vary in
number from two, in most teleosts, to forty or fifty in the holostean, Amia calva.
Embryologically they arise as evaginations of the pronephric duct and are situated
ventrally and posteriorly on the kidney, or they may lie caudally to this organ.
Since the original description of these corpuscles by STANNIUS in 1839, speculation about their function has been considerable. It has generally been thought
that they are endocrine glands, but this has yet to be established. RASQUIN (1956)
examined the histology of these tissues in the freshwater teleost, Astyanax rnexicanus, after it had been immersed in 1% sodium chloride solutions, or injected
with deoxycorticosterone. Cytological changes in the corpuscles that followed
such treatments suggested that they may be involved in osmoregulation. Ablation
of the corpuscles of STANNIUS in the eel results in a decreased plasma sodium level,
accompanied by an elevated concentration of potassium and calcium (LELoup-HATEY, 1964; M. FONTAINE, 1964). Such changes were ameliorated by the injection
of corpuscle tissue extracts. These results have been confirmed by CHAN et al.
(1967a), so that the evidence strongly supports the possibility of an osmoregulatory
role for these tissues.
The exact actions of the corpuscles of STANNIUS in osmotic regulation, and
the nature of their putative secretions are at present uncertain. Due probably to
the proximity of the STANNIUS corpuscles and the adrenocortical tissues in fishes,
the possibility that they are both parts of the same steroid secreting system has
been explored extensively. It should be noted, however, that the two groups of
tissues have distinct embryological origins and morphological sites, even though
they do both lie in the caudal regions of a fish. Many attempts have been made
to identify steroids in extracts of the corpuscles of STANNIUS, and to show formation and accumulation of such substances, after their in vitro incubation in the
presence or absence of steroid substrates. The results will be discussed in detail
in a later section, but they are variable and contradictory. There are some reports
of the presence of steroids (or steroid-like materials?) under certain conditions, but
78