2. THE NEUROHYPOPHYSIS
139
Squalus ucanthias, and perhaps of the sharks in general, is another,
unidentified principle or principles, probably containing valine and serine.
C. The Actions of Neurohypophysial Principles in the Elasmobranchs
Little is known of the functions of neurohypophysial principles in the
elasmobranchs. The few studies recorded have utilized mainly mammalian principles, which are different from those of the elasmobranchs themselves. Although there is no reason to assume that the functions of the
principles bear any close relationship to those seen in higher vertebrates,
most studies have been based on our knowledge of the mammalian
pattern.
There is no evidence that neurohypophysial principles affect the water
or salt balance of the elasmobranchs. The immersion of Scylwrhinus
caniculus in hypertonic seawater, enriched to 10% NaCl, failed to change
the pituitary content of neurohypophysial peptides, as judged by oxytocic
assay ( Perks and Dodd, 1960). However, it is possible that hypothalamic
production kept pace with systemic loss, and therefore this negative observation is inconclusive. The injection of 20 m u / kg (rat uterus oxytocic
activity) of a crude extract of Raia clavata pituitaries into four nurse
sharks, Ginglymostomu cirratum, caused no significant changes in their
body weights, and it would appear that there is no water-balance effect
analogous to that seen in the frog (Heller and Bentley, 1965). An antidiuretic action on the kidney is unlikely, since marine elasmobranchs do
not suffer the extremes of osmotic conditions which may affect a terrestial
vertebrate, and their urine production appears to be constantly and notably low ( 12.9 ml/kg/day, Squalus aunthim, Clarke, 1933; 15.8 ml/kg/
day, Mustelzcs h u i s , Kempton, 1953; 1.8 ml/ kg/ day, Scyliorhinus canicuZus, Perks, 1959; Dodd et al., 1966). Since water and osmotic balance are
achieved by urea conservation, it is possible that investigations of the
actions of neurohypophysial principles on urea metabolism could prove
well worthwhile, but at the present time there are no data available.
The fact that neurohypophysial principles affect sodium metabolism
in the lampreys and in the teleost fish might suggest that they have a
similar action in the elasmobranchs. However, neither 8 lysine vasopressin, nor an arginine-lysine vasopressin mixture appears to affect the
sodium-secreting rectal gland of Squalus ucanthias (Burger, 1962). Perhaps the use of the oxytocinlike elasmobranch principles--or even oxytocin itself-would have been more rewarding. It would have been closer
to the physiological situation in the elasmobranchs, and also more in
keeping with our knowledge of the teleosts, where oxytocinlike neutral
139
Squalus ucanthias, and perhaps of the sharks in general, is another,
unidentified principle or principles, probably containing valine and serine.
C. The Actions of Neurohypophysial Principles in the Elasmobranchs
Little is known of the functions of neurohypophysial principles in the
elasmobranchs. The few studies recorded have utilized mainly mammalian principles, which are different from those of the elasmobranchs themselves. Although there is no reason to assume that the functions of the
principles bear any close relationship to those seen in higher vertebrates,
most studies have been based on our knowledge of the mammalian
pattern.
There is no evidence that neurohypophysial principles affect the water
or salt balance of the elasmobranchs. The immersion of Scylwrhinus
caniculus in hypertonic seawater, enriched to 10% NaCl, failed to change
the pituitary content of neurohypophysial peptides, as judged by oxytocic
assay ( Perks and Dodd, 1960). However, it is possible that hypothalamic
production kept pace with systemic loss, and therefore this negative observation is inconclusive. The injection of 20 m u / kg (rat uterus oxytocic
activity) of a crude extract of Raia clavata pituitaries into four nurse
sharks, Ginglymostomu cirratum, caused no significant changes in their
body weights, and it would appear that there is no water-balance effect
analogous to that seen in the frog (Heller and Bentley, 1965). An antidiuretic action on the kidney is unlikely, since marine elasmobranchs do
not suffer the extremes of osmotic conditions which may affect a terrestial
vertebrate, and their urine production appears to be constantly and notably low ( 12.9 ml/kg/day, Squalus aunthim, Clarke, 1933; 15.8 ml/kg/
day, Mustelzcs h u i s , Kempton, 1953; 1.8 ml/ kg/ day, Scyliorhinus canicuZus, Perks, 1959; Dodd et al., 1966). Since water and osmotic balance are
achieved by urea conservation, it is possible that investigations of the
actions of neurohypophysial principles on urea metabolism could prove
well worthwhile, but at the present time there are no data available.
The fact that neurohypophysial principles affect sodium metabolism
in the lampreys and in the teleost fish might suggest that they have a
similar action in the elasmobranchs. However, neither 8 lysine vasopressin, nor an arginine-lysine vasopressin mixture appears to affect the
sodium-secreting rectal gland of Squalus ucanthias (Burger, 1962). Perhaps the use of the oxytocinlike elasmobranch principles--or even oxytocin itself-would have been more rewarding. It would have been closer
to the physiological situation in the elasmobranchs, and also more in
keeping with our knowledge of the teleosts, where oxytocinlike neutral