2. THE NEUROHYPOPHYSIS
183
0.5-0.6) was mainly oxytocic in activity and moved in a manner similar
to oxytocin, or to that of a related neutral peptide. Its pharmacological
properties were clearly different from those of 4 Ser, 8 Ile oxytocin, the
neutral principle typical of most bony fish. Follett and Heller (1964b)
noticed that the lungfish neutral peptide was similar to oxytocin in its
milk-ejection activity and in its magnesium potentiation, but the relatively
high avian depressor potency indicated that the two agents were not the
same. Follett and Heller (1964b) suggested that their results were compatable with the presence of 8 Ile oxytocin, a peptide which was known
to occur in amphibia. However, it was possible that this peptide could
be mixed with oxytocin or with some new principle. W. H. Sawyer
( 1965a), working with Protopterus aethwpicus, and using similar methods, was unable to find an unusually high avian depressor activity in the
neutral principle and was inclined to ascribe the actions to oxytocin itself.
Further, W. H. Sawyer (196613) was able to separate the active principles
by column chromatography on carboxymethyl cellulose resin. He confirmed the presence of a basic peptide with vasopressor, antidiuretic, and
frog bladder stimulating activities consistent with arginine vasotocin.
However, he found that the majority of the oxytocic activity was eluted
as a large peak in the position typical of oxytocin. It could not be distinguished from this peptide. Sawyer considered all the evidence available and concluded that probably the pituitaries of Protopterus aethwpicus contained oxytocin, 8 Ile oxytocin, or a mixture of the two, and that
the particular combination might vary with the individual, the race, the
location, the season, or the treatment of the tissues (W. H. Sawyer, 1965a,
1966b, 1968a). Indeed, it was known that there were considerable variations in the hormonal content of the lungfish pituitary, since the ratio
between the neutral oxytocic peptide and arginine vasotocin ranged from
about 2.6 to 25.0, as judged by the oxytocic and vasopressor assays
(vasopressor/oxytocic = 0.04 to 0.38) (Follett and Heller, 196413; W. H.
Sawyer, 19661,). However, the oxytocic principle was always present in
far greater quantities. A possible variation in the proportion of oxytocin
( ?) to 8 Ile oxytocin was supported by W. H. Sawyer’s studies ( 1968a)
on different batches of glands. One collection of glands appeared to
differ significantly from 8 Ile oxytocin and to parallel oxytocin itself.
The other three batches showed pharmacological similarities to 8 Ile
oxytocin. However, the general trend has been to establish the presence
of 8 Ile oxytocin more firmly, and W. H. Sawyer’s most recent studies
(1969) have indicated that at least some glands of Protopterus aethiopicus contain an overwhelming or total preponderance of 8 Ile oxytocin.
Nevertheless, there is still support for the possible presence of oxytocin
among other species of lungfish. In Lepidosiren paradoxa, thin-layer
183
0.5-0.6) was mainly oxytocic in activity and moved in a manner similar
to oxytocin, or to that of a related neutral peptide. Its pharmacological
properties were clearly different from those of 4 Ser, 8 Ile oxytocin, the
neutral principle typical of most bony fish. Follett and Heller (1964b)
noticed that the lungfish neutral peptide was similar to oxytocin in its
milk-ejection activity and in its magnesium potentiation, but the relatively
high avian depressor potency indicated that the two agents were not the
same. Follett and Heller (1964b) suggested that their results were compatable with the presence of 8 Ile oxytocin, a peptide which was known
to occur in amphibia. However, it was possible that this peptide could
be mixed with oxytocin or with some new principle. W. H. Sawyer
( 1965a), working with Protopterus aethwpicus, and using similar methods, was unable to find an unusually high avian depressor activity in the
neutral principle and was inclined to ascribe the actions to oxytocin itself.
Further, W. H. Sawyer (196613) was able to separate the active principles
by column chromatography on carboxymethyl cellulose resin. He confirmed the presence of a basic peptide with vasopressor, antidiuretic, and
frog bladder stimulating activities consistent with arginine vasotocin.
However, he found that the majority of the oxytocic activity was eluted
as a large peak in the position typical of oxytocin. It could not be distinguished from this peptide. Sawyer considered all the evidence available and concluded that probably the pituitaries of Protopterus aethwpicus contained oxytocin, 8 Ile oxytocin, or a mixture of the two, and that
the particular combination might vary with the individual, the race, the
location, the season, or the treatment of the tissues (W. H. Sawyer, 1965a,
1966b, 1968a). Indeed, it was known that there were considerable variations in the hormonal content of the lungfish pituitary, since the ratio
between the neutral oxytocic peptide and arginine vasotocin ranged from
about 2.6 to 25.0, as judged by the oxytocic and vasopressor assays
(vasopressor/oxytocic = 0.04 to 0.38) (Follett and Heller, 196413; W. H.
Sawyer, 19661,). However, the oxytocic principle was always present in
far greater quantities. A possible variation in the proportion of oxytocin
( ?) to 8 Ile oxytocin was supported by W. H. Sawyer’s studies ( 1968a)
on different batches of glands. One collection of glands appeared to
differ significantly from 8 Ile oxytocin and to parallel oxytocin itself.
The other three batches showed pharmacological similarities to 8 Ile
oxytocin. However, the general trend has been to establish the presence
of 8 Ile oxytocin more firmly, and W. H. Sawyer’s most recent studies
(1969) have indicated that at least some glands of Protopterus aethiopicus contain an overwhelming or total preponderance of 8 Ile oxytocin.
Nevertheless, there is still support for the possible presence of oxytocin
among other species of lungfish. In Lepidosiren paradoxa, thin-layer