2. THE NEUROHYPOPHYSIS
123
changes in osmolarity (Morris, 1960), this effect on sodium levels might
delay, and therefore buffer, the changes which follow slight, transitory
variations in the salinity of its relatively constant, deep-water environment. However, the original authors draw the careful conclusion that the
neurohypophysial peptides can affect the relationship between the extracellular and intracellular distribution of water and electrolytes. There is
a hint that the hagfish's own principle( s ) are more potent in the hagfish
than those of the mammals. A second possible effect of neurohypophysial
principles on the metabolism of the hagfish is an influence on water balance. Adam (1963a) observed that in Myxine glutinosa, the injection of
high doses of a mammalian vasopressin preparation (Pituifral, 100-1000
m u ) resulted in up to 7% rise in total body water. Clearly, there is need
for more extensive investigations, with the use of the principle( s ) native
to the hagfish pituitary.
Since water, salts, and gases might be exchanged readily by the gills,
it is interesting to note that the experiments of Somlyo and Somlyo (1968)
have suggested that neurohypophysial peptides might influence the
branchial circulation of the blood. They showed that isolated strips taken
from the ventral aorta of Eptatretus stoutii contracted to extremely low
doses of synthetic arginine vasotocin ( 10-lo M), and that higher doses of
oxytocin (0.1-100.0 mU/ml) and arginine vasopressin (1.0-100.0 mU/ml)
would produce a similar response. The isolated dorsal aorta behaved in a
similar way, but it was less sensitive, and it relaxed more readily. There
are no studies of more general effects of neurohypophysial principles on
the blood pressure or circulation of the hagfish.
At present, it is not possible to reach dependable conclusions on the
function of the neurohypophysis of the hagfish. Further study is made
more urgent by the demonstration of Gorbman et al. (1963) that the
hagfish neurohypophysis is unlikely to be concerned in the local control of
the adenohypophysis and is specially adapted to pour its secretions into
the systemic circulation.
2. PETROMYZONIFORMFS
Although experiments involving hypophysectomy have suggested that
the pituitary of the freshwater lamprey was not essential to life, the extent to which the pars nervosa had been removed is uncertain, and, in
any case, the intact preoptic nuclei might have continued to supply the
necessary hormones (Lampetra planeri, L. fluviatilis, Young, 1935; Dodd
et al., 1960).
Direct studies with neurohypophysial peptides have been confined
123
changes in osmolarity (Morris, 1960), this effect on sodium levels might
delay, and therefore buffer, the changes which follow slight, transitory
variations in the salinity of its relatively constant, deep-water environment. However, the original authors draw the careful conclusion that the
neurohypophysial peptides can affect the relationship between the extracellular and intracellular distribution of water and electrolytes. There is
a hint that the hagfish's own principle( s ) are more potent in the hagfish
than those of the mammals. A second possible effect of neurohypophysial
principles on the metabolism of the hagfish is an influence on water balance. Adam (1963a) observed that in Myxine glutinosa, the injection of
high doses of a mammalian vasopressin preparation (Pituifral, 100-1000
m u ) resulted in up to 7% rise in total body water. Clearly, there is need
for more extensive investigations, with the use of the principle( s ) native
to the hagfish pituitary.
Since water, salts, and gases might be exchanged readily by the gills,
it is interesting to note that the experiments of Somlyo and Somlyo (1968)
have suggested that neurohypophysial peptides might influence the
branchial circulation of the blood. They showed that isolated strips taken
from the ventral aorta of Eptatretus stoutii contracted to extremely low
doses of synthetic arginine vasotocin ( 10-lo M), and that higher doses of
oxytocin (0.1-100.0 mU/ml) and arginine vasopressin (1.0-100.0 mU/ml)
would produce a similar response. The isolated dorsal aorta behaved in a
similar way, but it was less sensitive, and it relaxed more readily. There
are no studies of more general effects of neurohypophysial principles on
the blood pressure or circulation of the hagfish.
At present, it is not possible to reach dependable conclusions on the
function of the neurohypophysis of the hagfish. Further study is made
more urgent by the demonstration of Gorbman et al. (1963) that the
hagfish neurohypophysis is unlikely to be concerned in the local control of
the adenohypophysis and is specially adapted to pour its secretions into
the systemic circulation.
2. PETROMYZONIFORMFS
Although experiments involving hypophysectomy have suggested that
the pituitary of the freshwater lamprey was not essential to life, the extent to which the pars nervosa had been removed is uncertain, and, in
any case, the intact preoptic nuclei might have continued to supply the
necessary hormones (Lampetra planeri, L. fluviatilis, Young, 1935; Dodd
et al., 1960).
Direct studies with neurohypophysial peptides have been confined