174
A. M. PERKS
responds with a marked fall in its neurosecretory level (Fridberg and
Olsson, 1959). Although this anomaly may be explained by possible depletion by “stress,” it may emphasize the fact that the amount of neurosecretory or biologically active material present in the neurohypophysis
is always a balance between the rate of hypothalamic supply and the rate
of pituitary release into the circulation. Therefore, the important point
made by these experiments is not the direction of the change but the fact
that a change has occurred.
Despite these responses to changes in the tonicity of the environment,
it is clear that the injection of neurohypophysial peptides into teleost fish
does not have any water-balance effect of the type seen in the frog
( Cyprinus carpw, Perca fhvescens; Fontaine, 1956; Maetz, 1963). This
has been confirmed by the administration of pure arginine vasotocin (36
mpmoles/ kg ) to Trichogaster trichopterus, where there was no detectable
change in body weight ( Heller and Bentley, 1965). Although infrequent
antidiuretic effects have been seen in the teleost kidney (Salmo gairdneri,
R. M. Holmes, 1961; Carassius auratus, Maetz et aZ., 1964), most attention has been focused on the strong diuretic response which usually follows injections of arginine-lysine vasopressin, oxytocin, arginine vasotocin, or teleost pituitary extracts into Carassius auratus (Sexton, 1955;
Maetz, 1963). The concentration of sodium in the urine does not change,
so that sodium loss is parallel to the diuresis (see W. H. Sawyer, 1965a).
It is probable that this response results from an increase in the glomerular
filtration rate (Carassius auratus, Maetz, 1963; W. H. Sawyer, 1965a).
W. N. Holmes and McBean (1%) have shown that injections of 100 mU
of either oxytocin or vasopressin will nearly double the glomerular filtration rate of Salmo gairdneri. Recently, this explanation has been supported by the observation that arginine vasotocin failed to cause a diuresis
in the aglomerular kidney of Opsanus tau, even though it caused pressor
effects (Lahlou et al., 1968). However, the situation may be more complicated in some circumstances, since W. N. Holmes (1959) noted that
a high dose (loo0 m u ) of mammalian vasopressin caused a reduction in
sodium output, ascribed to the kidney, in Salmo gairdneri, and Dlouhh
et al. (1967) have suggested that oxytocin causes reabsorption of sodium
in the kidney of Myoxocephalus scorppius. Indeed, the physiological significance of the diuresis which follows the administration of neurohypophysial peptides is not clear, since it requires the use of high doses
of hormones ( W. H. Sawyer, 1965a). Further, a number of workers have
noted that there is a profound fall-not a rise-in glomerular filtration
rate when freshwater fish enter a marine environment-and this is at a
time when loss of neurosecretory material from the neurohypophysis is
supposed to take place (Salmo gairdneri, W. N. Holmes and McBean,
A. M. PERKS
responds with a marked fall in its neurosecretory level (Fridberg and
Olsson, 1959). Although this anomaly may be explained by possible depletion by “stress,” it may emphasize the fact that the amount of neurosecretory or biologically active material present in the neurohypophysis
is always a balance between the rate of hypothalamic supply and the rate
of pituitary release into the circulation. Therefore, the important point
made by these experiments is not the direction of the change but the fact
that a change has occurred.
Despite these responses to changes in the tonicity of the environment,
it is clear that the injection of neurohypophysial peptides into teleost fish
does not have any water-balance effect of the type seen in the frog
( Cyprinus carpw, Perca fhvescens; Fontaine, 1956; Maetz, 1963). This
has been confirmed by the administration of pure arginine vasotocin (36
mpmoles/ kg ) to Trichogaster trichopterus, where there was no detectable
change in body weight ( Heller and Bentley, 1965). Although infrequent
antidiuretic effects have been seen in the teleost kidney (Salmo gairdneri,
R. M. Holmes, 1961; Carassius auratus, Maetz et aZ., 1964), most attention has been focused on the strong diuretic response which usually follows injections of arginine-lysine vasopressin, oxytocin, arginine vasotocin, or teleost pituitary extracts into Carassius auratus (Sexton, 1955;
Maetz, 1963). The concentration of sodium in the urine does not change,
so that sodium loss is parallel to the diuresis (see W. H. Sawyer, 1965a).
It is probable that this response results from an increase in the glomerular
filtration rate (Carassius auratus, Maetz, 1963; W. H. Sawyer, 1965a).
W. N. Holmes and McBean (1%) have shown that injections of 100 mU
of either oxytocin or vasopressin will nearly double the glomerular filtration rate of Salmo gairdneri. Recently, this explanation has been supported by the observation that arginine vasotocin failed to cause a diuresis
in the aglomerular kidney of Opsanus tau, even though it caused pressor
effects (Lahlou et al., 1968). However, the situation may be more complicated in some circumstances, since W. N. Holmes (1959) noted that
a high dose (loo0 m u ) of mammalian vasopressin caused a reduction in
sodium output, ascribed to the kidney, in Salmo gairdneri, and Dlouhh
et al. (1967) have suggested that oxytocin causes reabsorption of sodium
in the kidney of Myoxocephalus scorppius. Indeed, the physiological significance of the diuresis which follows the administration of neurohypophysial peptides is not clear, since it requires the use of high doses
of hormones ( W. H. Sawyer, 1965a). Further, a number of workers have
noted that there is a profound fall-not a rise-in glomerular filtration
rate when freshwater fish enter a marine environment-and this is at a
time when loss of neurosecretory material from the neurohypophysis is
supposed to take place (Salmo gairdneri, W. N. Holmes and McBean,