the plasma electrolytes, also stimulates secretion. It was thus suggested that secretion from the gland may be responsive to changes in volume, rather than concentration of the body fluids. In further contrast to the avian salt gland, no evidence of a neural control mechanism has been found, and the injection of vasopressin is without effect (BURGER, 1962). CHAN et al. (1967 b) also found that vasopressin, as well as oxytocin, did not alter secretion from the rectal gland of the lip
shark, but cortisol injections decreased both the flow and concentration of this
fluid. It is unknown whether this latter effect reflects a physiological or only a
pharmacological action. BURGER (1962; 1965) suggested that 'volume receptors'
may control the gland's secretion through the intervention of some ' undefined hormone'. At present we do not know what this is.
The hormones present in chondrichthyeans, and which are potentially con -
cerned with osmoregulation, have been described earlier in this chapter (Tables
7.4 and 7.5); pep tides are present in the neurohypophysis, cortisol, corticosterone
and, at least in one species, large quantities of 1 -hydroxycorticosterone are present
in the plasma. This steroid can stimulate sodium transport across membranes and
when tested on the toad urinary bladder has 80% of the activity of aldosterone
(GRIMM, O'HALLORAN, and IDLER, 1969). The inte rrenal tissues of at least eleven
species of chondrichthyeans can produce 1 a-hydroxycorticosterone in vitro suggesting that it may also have a widespread distribution in the plasma of these fishes .
Nevertheless, its role in the chondrichthyeans is unknown. The adenohypophysis
also contains a ' prolactin-like' product and (probably) corticotrophin. There is,
however, little information about how these secretions affect the osmoregulation
of such fish .
Hypophysectomy has been performed in a number of chondrichthyeans, the
object most often being to disturb the fishes' chromatic behaviour rather than their
osmoregulation (see HOAR, 1966), but such fish appear to survive quite well in seawater. A closer exam ination of such deficient fish may, nevertheless, divulge some
changes. Sharks and rays do not survive interrenalectomy for long but no prominent changes in their electrolyte metabolism have been reported (HARTMAN et al.,
1944). Interrenalectorny has been performed more recently on the skate, Raja
erinacea (IDLER, O'HALLORAN, and HORNE , 1969). These fish survived at least 3
to 4 weeks and suffered no significant adverse changes in their liver glycogen levels .
An account of the osmoregulation of these fish will be eagerly awaited .
Extracts of the neurohypophysis of chondrichthyeans do not alter overall water
balance (weight change) when in jected into nurse sharks, Ginglymostoma cirratum
(HELLER and BENTLEY, 1965). CHAN et al. (1967b) found that cortisol did not
change the plasma electrolyte concentrations of lip sharks, but that there was a rise
in the muscle potassium levels due to loss of cell water. Such an effect could indirectly result from a sodium retention resulting in the expansion of the extracellular
space at the expense of some cell water. As 1 a-hydroxycorticosterone appears to
be a major interrenal steroid in many species of sharks, skates and rays it will be
most interesting to see if it affects the salt and water metabolism of such fishes . The
role of endocrines in the osmoregulation of sharks is a field that has been little investigated and only requires the facilities and courage to handle such beasts.
Adaptation of sharks and rays to fresh water. Most chondrichthyeans live in
the sea but some frequent and may even live their entire lives, in fresh water. Such
250
shark, but cortisol injections decreased both the flow and concentration of this
fluid. It is unknown whether this latter effect reflects a physiological or only a
pharmacological action. BURGER (1962; 1965) suggested that 'volume receptors'
may control the gland's secretion through the intervention of some ' undefined hormone'. At present we do not know what this is.
The hormones present in chondrichthyeans, and which are potentially con -
cerned with osmoregulation, have been described earlier in this chapter (Tables
7.4 and 7.5); pep tides are present in the neurohypophysis, cortisol, corticosterone
and, at least in one species, large quantities of 1 -hydroxycorticosterone are present
in the plasma. This steroid can stimulate sodium transport across membranes and
when tested on the toad urinary bladder has 80% of the activity of aldosterone
(GRIMM, O'HALLORAN, and IDLER, 1969). The inte rrenal tissues of at least eleven
species of chondrichthyeans can produce 1 a-hydroxycorticosterone in vitro suggesting that it may also have a widespread distribution in the plasma of these fishes .
Nevertheless, its role in the chondrichthyeans is unknown. The adenohypophysis
also contains a ' prolactin-like' product and (probably) corticotrophin. There is,
however, little information about how these secretions affect the osmoregulation
of such fish .
Hypophysectomy has been performed in a number of chondrichthyeans, the
object most often being to disturb the fishes' chromatic behaviour rather than their
osmoregulation (see HOAR, 1966), but such fish appear to survive quite well in seawater. A closer exam ination of such deficient fish may, nevertheless, divulge some
changes. Sharks and rays do not survive interrenalectomy for long but no prominent changes in their electrolyte metabolism have been reported (HARTMAN et al.,
1944). Interrenalectorny has been performed more recently on the skate, Raja
erinacea (IDLER, O'HALLORAN, and HORNE , 1969). These fish survived at least 3
to 4 weeks and suffered no significant adverse changes in their liver glycogen levels .
An account of the osmoregulation of these fish will be eagerly awaited .
Extracts of the neurohypophysis of chondrichthyeans do not alter overall water
balance (weight change) when in jected into nurse sharks, Ginglymostoma cirratum
(HELLER and BENTLEY, 1965). CHAN et al. (1967b) found that cortisol did not
change the plasma electrolyte concentrations of lip sharks, but that there was a rise
in the muscle potassium levels due to loss of cell water. Such an effect could indirectly result from a sodium retention resulting in the expansion of the extracellular
space at the expense of some cell water. As 1 a-hydroxycorticosterone appears to
be a major interrenal steroid in many species of sharks, skates and rays it will be
most interesting to see if it affects the salt and water metabolism of such fishes . The
role of endocrines in the osmoregulation of sharks is a field that has been little investigated and only requires the facilities and courage to handle such beasts.
Adaptation of sharks and rays to fresh water. Most chondrichthyeans live in
the sea but some frequent and may even live their entire lives, in fresh water. Such
250