138
A. M. PERKS
19f37; 110 U/mg, Heinicke and Perks, 1969a), and lower than that of pure
oxytocin (430 U/mg). The purified peptide from Raiu ocelluta gave a
ratio of rabbit milk-ejection: rat uterus: antidiuretic activities of 8.5: 1:
0.04. At the time, this unusually high milk-ejection potency suggested
that it was a new principle, different from that found in other elasmobranch species. Amino acid analyses showed that it contained cystine,
tyrosine, isoleucine, serine, asparagine, proline, glutamine, and glycine,
in ratios compatible with a neurohypophysial principle. Soon afterward, Acher and his co-workers purified extracts from Raia clavata,
R. batis, R. m e w s , and R. fullonica (Acher et al., 1965a, 1967;
Chauvet et al., 1965). They found small amounts of arginine vasotocin, together with a major oxytocic component which contained
the same amino acids as were present in the peptide from Raia ocellata. The principle was identified as 4 Ser, 8 Gln oxytocin. At the time,
the high magnesium potentiation of this material (10-fold) appeared to
differentiate it from the principle of Raia ocelluta (2.6-fold), but this
criterion has been shown to be variable and unreliable in elasmobranch
work ( Heinicke and Perks, 19691, ) . The other biological data given for 4
Ser, 8 Gln oxytocin were insufficient to establish any possible identity
between this peptide and the principle of Raia ocelluta. However,
Heinicke and Perks ( 1969a) have shown that the oxytocic peptide of Raia
ocelluta has the same pharmacological spectrum as that of Raia rhina,
and W. H. Sawyer et al. (1969) have demonstrated that there is a close
parallel between the biological properties of the principle of Raia rhina
and those of synthetic 4 Ser, 8 Gln oxytocin, when they are assayed directly against one another. Therefore, it is probable that 4 Ser, 8 Gln
oxytocin is the main oxytocic principle of all species of skate so far
examined.
In contrast to the skate, direct assays of extracts from Squalus manthias against synthetic 4 Ser, 8 Gln oxytocin have shown marked differences between the two active agents. This is particularly true of their
rabbit milk-ejection and rat antidiuretic potencies (W. H. Sawyer et al.,
1969). Preliminary amino acid analyses do not suggest the presence of
4 Ser, 8 Gln oxytocin, but they raise the possibility of a serine-valine containing peptide or of a mixture of such peptides (Heinicke and Perks,
1969a). It is too early to make any clear statement on the nature of the
principle of Squalus acanthias, but it is clear that it is different from that
of the skates. This raises the interesting possibility that the skates and
sharks possess different neurohypophysial peptides.
It is concluded that the elasmobranchs possess traces of arginine
vasotocin, together with at least one major neutral peptide. While the
neutral peptide of the skates is probably 4 Ser, 8 Gln oxytocin, that of
A. M. PERKS
19f37; 110 U/mg, Heinicke and Perks, 1969a), and lower than that of pure
oxytocin (430 U/mg). The purified peptide from Raiu ocelluta gave a
ratio of rabbit milk-ejection: rat uterus: antidiuretic activities of 8.5: 1:
0.04. At the time, this unusually high milk-ejection potency suggested
that it was a new principle, different from that found in other elasmobranch species. Amino acid analyses showed that it contained cystine,
tyrosine, isoleucine, serine, asparagine, proline, glutamine, and glycine,
in ratios compatible with a neurohypophysial principle. Soon afterward, Acher and his co-workers purified extracts from Raia clavata,
R. batis, R. m e w s , and R. fullonica (Acher et al., 1965a, 1967;
Chauvet et al., 1965). They found small amounts of arginine vasotocin, together with a major oxytocic component which contained
the same amino acids as were present in the peptide from Raia ocellata. The principle was identified as 4 Ser, 8 Gln oxytocin. At the time,
the high magnesium potentiation of this material (10-fold) appeared to
differentiate it from the principle of Raia ocelluta (2.6-fold), but this
criterion has been shown to be variable and unreliable in elasmobranch
work ( Heinicke and Perks, 19691, ) . The other biological data given for 4
Ser, 8 Gln oxytocin were insufficient to establish any possible identity
between this peptide and the principle of Raia ocelluta. However,
Heinicke and Perks ( 1969a) have shown that the oxytocic peptide of Raia
ocelluta has the same pharmacological spectrum as that of Raia rhina,
and W. H. Sawyer et al. (1969) have demonstrated that there is a close
parallel between the biological properties of the principle of Raia rhina
and those of synthetic 4 Ser, 8 Gln oxytocin, when they are assayed directly against one another. Therefore, it is probable that 4 Ser, 8 Gln
oxytocin is the main oxytocic principle of all species of skate so far
examined.
In contrast to the skate, direct assays of extracts from Squalus manthias against synthetic 4 Ser, 8 Gln oxytocin have shown marked differences between the two active agents. This is particularly true of their
rabbit milk-ejection and rat antidiuretic potencies (W. H. Sawyer et al.,
1969). Preliminary amino acid analyses do not suggest the presence of
4 Ser, 8 Gln oxytocin, but they raise the possibility of a serine-valine containing peptide or of a mixture of such peptides (Heinicke and Perks,
1969a). It is too early to make any clear statement on the nature of the
principle of Squalus acanthias, but it is clear that it is different from that
of the skates. This raises the interesting possibility that the skates and
sharks possess different neurohypophysial peptides.
It is concluded that the elasmobranchs possess traces of arginine
vasotocin, together with at least one major neutral peptide. While the
neutral peptide of the skates is probably 4 Ser, 8 Gln oxytocin, that of