170
A. M. PERKS
physial cells and externally to the body tissues. However, there is no
guarantee that the active agents carried in each of the two circuits are
necessarily chemically similar.
It is clear that the teleost neurohypophysis has undergone considerable
specialization. Two specializations appear particularly important: one is
the absence, or profound reduction of the pituitary portal system, and the
other is the development of direct neural contacts with the entire adenohypophysial complex. It is natural to wonder whether these notable modifications could be interrelated. Since pituitary portal systems appear to
exist in more primitive vertebrates, and there are suggestions that they
are present in the preteleost bony fish, it would seem possible that the
development of direct nervous innervation in the teleosts has made a
portal form of control obsolete. In this case, the portal system may have
become almost nonexistent. It is possible that the median eminence is
represented by the small subterminal area of Leatherland et al. (1966).
It is also possible, and perhaps more likely, that the median eminence
became incorporated into the pituitary as the rostra1 region of the pars
nervosa. Whatever the true relationships may prove to be, anatomical
considerations suggest that the neurohypophysis may control the adenohypophysis either by direct nervous action or by a diffuse liberation of
active agents into its general blood supply. Similarly, it may influence the
pars intermedia either by direct neural contact or by passing active agents
into the intervascular channel where this exists. Finally, the neurohypophysis may pass hormones into the general circulation and control
particular organs throughout the body.
B. The Nature of the Neurohypophysial Principles of the Teleosts
As early as 1941, Heller (1941b) had demonstrated that pituitaries
from Gadus sp. contained far more frog water-balance activity than could
be accounted for by the presence of mammalian principles. In 1959,
Pickering and Heller adapted paper chromatography to the study of extracts from Gadus sp., Salmo sp., and Pollachius uirens, and succeeded in
separating the “frog water-balance factor” from an oxytocinlike agent.
They found that almost all the pressor and antidiuretic activity of the
extract was localized with the frog water-balance factor. At the same
time, W. H. Sawyer et al. (1959, 1961) showed that crude extracts from
the pituitaries of Pollachius uirens possessed remarkably strong activity
on the frog bladder and on the hen oviduct. They suggested that these
actions, together with the results of other biological assays, could be
accounted for by a mixture of oxytocin and arginine vasotocin-a peptide
A. M. PERKS
physial cells and externally to the body tissues. However, there is no
guarantee that the active agents carried in each of the two circuits are
necessarily chemically similar.
It is clear that the teleost neurohypophysis has undergone considerable
specialization. Two specializations appear particularly important: one is
the absence, or profound reduction of the pituitary portal system, and the
other is the development of direct neural contacts with the entire adenohypophysial complex. It is natural to wonder whether these notable modifications could be interrelated. Since pituitary portal systems appear to
exist in more primitive vertebrates, and there are suggestions that they
are present in the preteleost bony fish, it would seem possible that the
development of direct nervous innervation in the teleosts has made a
portal form of control obsolete. In this case, the portal system may have
become almost nonexistent. It is possible that the median eminence is
represented by the small subterminal area of Leatherland et al. (1966).
It is also possible, and perhaps more likely, that the median eminence
became incorporated into the pituitary as the rostra1 region of the pars
nervosa. Whatever the true relationships may prove to be, anatomical
considerations suggest that the neurohypophysis may control the adenohypophysis either by direct nervous action or by a diffuse liberation of
active agents into its general blood supply. Similarly, it may influence the
pars intermedia either by direct neural contact or by passing active agents
into the intervascular channel where this exists. Finally, the neurohypophysis may pass hormones into the general circulation and control
particular organs throughout the body.
B. The Nature of the Neurohypophysial Principles of the Teleosts
As early as 1941, Heller (1941b) had demonstrated that pituitaries
from Gadus sp. contained far more frog water-balance activity than could
be accounted for by the presence of mammalian principles. In 1959,
Pickering and Heller adapted paper chromatography to the study of extracts from Gadus sp., Salmo sp., and Pollachius uirens, and succeeded in
separating the “frog water-balance factor” from an oxytocinlike agent.
They found that almost all the pressor and antidiuretic activity of the
extract was localized with the frog water-balance factor. At the same
time, W. H. Sawyer et al. (1959, 1961) showed that crude extracts from
the pituitaries of Pollachius uirens possessed remarkably strong activity
on the frog bladder and on the hen oviduct. They suggested that these
actions, together with the results of other biological assays, could be
accounted for by a mixture of oxytocin and arginine vasotocin-a peptide