2. THE NEUROHYPOPHYSIS
137
high levels, no El-type oxytocic principle could be separated on the
chromatograms. In 1967, W. H. Sawyer carried out essentially similar
experiments on Squalus acanthias and found that the great majority of
the oxytocic activity ran as a fast-moving, homogeneous E,-type peak.
However, he detected a slow-running moiety, present in trace amounts,
which corresponded to arginine vasotocin. Swiatkiewitz et al. (1967)
confirmed this by demonstrating a slow-running region of high frog
bladder and antidiuretic activity in their chromatograms; however, in
their experiments, the level of this arginine vasotocinlike principle was
never sufficient to show up as a second oxytocic peak. The presence of
arginine vasotocin was not unexpected since it had been found in trace
amounts (1% of the total oxytocic activity) in Squalus acanthias by W. H.
Sawyer ( 1965b) and in Raiu clavata by Acher et al. ( 1965a). Heller and
his co-workers did not measure pressor, antidiuretic, or frog bladder activities in their slow-running El peak. Their estimations of avian depressor
activity could have been affected by contaminating vasodepressor substances-and these have been shown to exist in elasmobranch extracts,
at least in terms of the rat blood pressure (Perks and Dodd, 1963a).
Further, the high magnesium potentiation, which was the most notable
characteristic of the E, peak, has been shown to be a variable and unreliable criterion for identifying elasmobranch principles ( Heinicke and
Perks, 1969b). Finally, the ratio of milk-ejection:rat uterus oxytocic activity ( -Mg2+) of the slow-running El peak of Raia clauata, which was
1.77 ( 1.47-2.07) (Heller and Roy, 1965a), is unlikely to be significantly
different from the values of approximately 1.8 and 2.2 given for synthetic
arginine vasotocin by Berde et al. ( 1962), and by W. H. Sawyer ( 1965b),
respectively. Therefore, it is possible that the slow-running principle of
Heller and his co-workers represents arginine vasotocin, perhaps contaminated by small quantities of vasodepressor substances, and by variable amounts of the major oxytocic principle, which might trail behind
if any degree of overloading had occurred. However, it is still possible
that the slow-moving moiety is a new peptide, which might fluctuate
with the season, reproductive cycles, or other unknown factors. Further
studies are needed to resolve this situation, but we can be certain that
most elasmobranchs contain at least one neutral oxytocinlike principle,
together with small quantities of arginine vasotocin.
The first purification and amino acid analysis of a major elasmobranch
principle was that carried out by Perks and Sawyer in 1965. Extracts from
Raia ocellata were purified by gel filtration and ion exchange chromatography on CM-Sephadex resin. The purified product appeared to have a
specific oxytocic activity of 17.6 U/mg, which was lower than that of the
principle later purified from Squalus acanthias (70 U/mg; W. H. Sawyer,
137
high levels, no El-type oxytocic principle could be separated on the
chromatograms. In 1967, W. H. Sawyer carried out essentially similar
experiments on Squalus acanthias and found that the great majority of
the oxytocic activity ran as a fast-moving, homogeneous E,-type peak.
However, he detected a slow-running moiety, present in trace amounts,
which corresponded to arginine vasotocin. Swiatkiewitz et al. (1967)
confirmed this by demonstrating a slow-running region of high frog
bladder and antidiuretic activity in their chromatograms; however, in
their experiments, the level of this arginine vasotocinlike principle was
never sufficient to show up as a second oxytocic peak. The presence of
arginine vasotocin was not unexpected since it had been found in trace
amounts (1% of the total oxytocic activity) in Squalus acanthias by W. H.
Sawyer ( 1965b) and in Raiu clavata by Acher et al. ( 1965a). Heller and
his co-workers did not measure pressor, antidiuretic, or frog bladder activities in their slow-running El peak. Their estimations of avian depressor
activity could have been affected by contaminating vasodepressor substances-and these have been shown to exist in elasmobranch extracts,
at least in terms of the rat blood pressure (Perks and Dodd, 1963a).
Further, the high magnesium potentiation, which was the most notable
characteristic of the E, peak, has been shown to be a variable and unreliable criterion for identifying elasmobranch principles ( Heinicke and
Perks, 1969b). Finally, the ratio of milk-ejection:rat uterus oxytocic activity ( -Mg2+) of the slow-running El peak of Raia clauata, which was
1.77 ( 1.47-2.07) (Heller and Roy, 1965a), is unlikely to be significantly
different from the values of approximately 1.8 and 2.2 given for synthetic
arginine vasotocin by Berde et al. ( 1962), and by W. H. Sawyer ( 1965b),
respectively. Therefore, it is possible that the slow-running principle of
Heller and his co-workers represents arginine vasotocin, perhaps contaminated by small quantities of vasodepressor substances, and by variable amounts of the major oxytocic principle, which might trail behind
if any degree of overloading had occurred. However, it is still possible
that the slow-moving moiety is a new peptide, which might fluctuate
with the season, reproductive cycles, or other unknown factors. Further
studies are needed to resolve this situation, but we can be certain that
most elasmobranchs contain at least one neutral oxytocinlike principle,
together with small quantities of arginine vasotocin.
The first purification and amino acid analysis of a major elasmobranch
principle was that carried out by Perks and Sawyer in 1965. Extracts from
Raia ocellata were purified by gel filtration and ion exchange chromatography on CM-Sephadex resin. The purified product appeared to have a
specific oxytocic activity of 17.6 U/mg, which was lower than that of the
principle later purified from Squalus acanthias (70 U/mg; W. H. Sawyer,