2. THE NEUROHYPOPHYSIS
185
the amphibians has been reached, with the hagfish the only possible
exception.
Although there is no general water-balance effect, neurohypophysial
principles do appear to affect the kidney. In Protopterus aethiopicw, the
injection of arginine vasotocin by either the intraperitoneal route (500
ng/kg) or by the intravenous method (10-50 ng/kg) resulted in a marked
increase in the volume of the urine (W. H. Sawyer, 1966b, 1968~).
Oxytocin (4000 ng/ kg) caused small, inconsistent diuretic responses, but
8 Ile oxytocin (4000 ng/kg) had little or no diuretic effect when given
into the peritoneal cavity (W. H. Sawyer, 1965a, 1966b). Again, it is not
known whether an antidiuretic effect would be elicited during the dry
season (W. H. Sawyer, 1966b). In part, the diuretic effect could result
from the increase in glomerular filtration rate which was observed, but
unlike the situation in such teleosts as Carassius auratus other factors
may be involved since the sodium concentration of the urine was also
increased (W. H. Sawyer, 1965a, 1966b, 1968~). It is possible that the
rise in urinary sodium was caused by depression or sodium reabsorption
by the kidney tubules (W. H. Sawyer, 1965a). Arginine vasotocin (500
nglkg) was particularly potent in increasing sodium excretion in the
urine, which may rise several hundredfold under its influence; in contrast,
oxytocin (4000 ng/kg) had a slight effect, and 8 Ile oxytocin (4000
ng/kg) was ineffective (W. H. Sawyer, 1966b). When arginine vasotocin
was given by the intravenous route, doses as low as 10-50 ng/kg caused
loss of sodium in the urine. This partly answers the criticism that the
doses required to produce natriuretic responses by the intraperitoneal
route are so great that the pituitary hormone content is barely sufficient
for a single response. Problems of this type have been discussed during
considerations of the lampreys (Section 11, C). Although an effect on the
sodium content of the urine has been observed a number of times, it is
not clear whether the principles affect sodium loss by other extrarenal
routes. However, their action causes an increase in the net loss of sodium
from the body (Heller and Bentley, 1963, 1965; W. H. Sawyer, 1965a).
The physiological significance of this enforced sodium loss is difficult to
see since it would appear to be detrimental to a totally freshwater
animal (see W. H. Sawyer, 1966b). Perhaps its effects are normally in a
delicate state of balance with opposing influences, similar to the antagonism seen between insulin and glucagon in the control of mammalian
blood sugar. Further work is needed.
The diuretic response of the kidney to neurohypophysial peptides
may be partly related to the increase in glomerular filtration rate which
also occurs. W. H. Sawyer (1968~) has considered the possibility that this
rise in filtration rate could be mediated by direct vascular effects. The
185
the amphibians has been reached, with the hagfish the only possible
exception.
Although there is no general water-balance effect, neurohypophysial
principles do appear to affect the kidney. In Protopterus aethiopicw, the
injection of arginine vasotocin by either the intraperitoneal route (500
ng/kg) or by the intravenous method (10-50 ng/kg) resulted in a marked
increase in the volume of the urine (W. H. Sawyer, 1966b, 1968~).
Oxytocin (4000 ng/ kg) caused small, inconsistent diuretic responses, but
8 Ile oxytocin (4000 ng/kg) had little or no diuretic effect when given
into the peritoneal cavity (W. H. Sawyer, 1965a, 1966b). Again, it is not
known whether an antidiuretic effect would be elicited during the dry
season (W. H. Sawyer, 1966b). In part, the diuretic effect could result
from the increase in glomerular filtration rate which was observed, but
unlike the situation in such teleosts as Carassius auratus other factors
may be involved since the sodium concentration of the urine was also
increased (W. H. Sawyer, 1965a, 1966b, 1968~). It is possible that the
rise in urinary sodium was caused by depression or sodium reabsorption
by the kidney tubules (W. H. Sawyer, 1965a). Arginine vasotocin (500
nglkg) was particularly potent in increasing sodium excretion in the
urine, which may rise several hundredfold under its influence; in contrast,
oxytocin (4000 ng/kg) had a slight effect, and 8 Ile oxytocin (4000
ng/kg) was ineffective (W. H. Sawyer, 1966b). When arginine vasotocin
was given by the intravenous route, doses as low as 10-50 ng/kg caused
loss of sodium in the urine. This partly answers the criticism that the
doses required to produce natriuretic responses by the intraperitoneal
route are so great that the pituitary hormone content is barely sufficient
for a single response. Problems of this type have been discussed during
considerations of the lampreys (Section 11, C). Although an effect on the
sodium content of the urine has been observed a number of times, it is
not clear whether the principles affect sodium loss by other extrarenal
routes. However, their action causes an increase in the net loss of sodium
from the body (Heller and Bentley, 1963, 1965; W. H. Sawyer, 1965a).
The physiological significance of this enforced sodium loss is difficult to
see since it would appear to be detrimental to a totally freshwater
animal (see W. H. Sawyer, 1966b). Perhaps its effects are normally in a
delicate state of balance with opposing influences, similar to the antagonism seen between insulin and glucagon in the control of mammalian
blood sugar. Further work is needed.
The diuretic response of the kidney to neurohypophysial peptides
may be partly related to the increase in glomerular filtration rate which
also occurs. W. H. Sawyer (1968~) has considered the possibility that this
rise in filtration rate could be mediated by direct vascular effects. The