retic effect when injected into rats. However, its properties were not identical with
those of mammalian neurohypophysial peptides, as it exerted a far more potent
'water balance effect' (water retention) when injected into frogs . The activity in
the neurohypophysis of the grass snake was later (HELLER and PICKERING, 1961)
shown to be pharmacologically identical with 8-arg101Oe-oxytocin (vasotocin). A
second peptide, similar in its properties to mammalian oxytocin, was also found
in the grass snake. The caiman neurohypophysis was found to contain vasotocin,
but a second activity could not be identified in this species, though both were found
in the green turtle, Chelonia mydas (SAWYER, MUNSICK, and VAN DYKE, 1961). Vasotocins have since been identified in other groups (Table 5.6), including the snakes,
in which their structure has been confirmed by amino acid analysis (PICKERING,
1967; ACHER, CHAUVET, and CHAUVET, 1968). The second peptide activity that was
found initially in most of the reptiles examined has been pharmacologically identified as 8-ileu-oxytocin (mesotocin) in the rattlesnake (MUNSICK, 1966) and found
chemically to be such in the viper, cobra and elaph (ACHER et al., 1968; ACHER,
CHAUVET, and CHAUVET, 1969a). PICKERING (1967) found that amino acid analysis,
indicated both the presence of mesotocin and oxytocin in the neurohypophysis
of the cobra and FOLLETT (1967) has presented tentative pharmacological evidence
to suggest that this may also be so in other reptiles. ACHER et al. (1969 a) emphasize
that they are unable chemically to detect oxytocin in the viper, cobra or elaph. PICKERING also found an additional peptide, similar to vasotocin, in the cobra, but this
has not yet been exhaustively characterized. Few results indicating concentrations
of such peptides 10 reptiles are available, but in the grass snake the level of vasotocin
is about 4 - 9 X 10.
9
M kg body weight (calc. from HELLER and PICKERING, 1961;
FOLLETT, 1967), a value comparable with those in other tetrapods. There is usually
2 - 4 times as much vasotocin as the other active peptides.
Mammalian neurohypophysial peptide preparations have been shown to exert
an antidiuretic effect when injected into the alligator and into Trachysaurus rugosus
(Table 5.7). Extracts of reptilian neurohypophyses also exert such an action when
injected back into the contributing species . DANTZLER (1967 a) has made a careful
analysis of the actions of vasotocin, mesotocin and oxytocin on the renal function
of the water snake Natrix sipedon. All of these neurohypophysial peptides can produce an antidiuresis, but mesotocin and oxytocin are only effective in large doses
that are always associated with a reduced GFR and a decrease in blood pressure.
Vasotocin reduces urine flow in small doses that have no action on blood pressure
and acts both by reducing the GFR and by increasing tubular water reabsorption.
The renal tubular action of vasotocin has a lower dose-response threshold than
its glomerular effects . The results suggested that the decreased GFR was due to
a reduction in the number of active glomeruli. It is uncertain whether vasotocin
has this pattern of action throughout the Reptilia for, as we have seen, there is a
considerable diversity in the renal processes of this group. Injection of large
amounts of Pitressin into the alligator thus was found to reduce the GFR without
affecting tubular absorption but such experiments should be repeated using small
doses of vasotocin.
The evidence for a physiological role of neurohypophysial peptides in controlling urine flow in reptiles remains circumstantial, and less complete than in any
other tetrapod group. Unfortunately the effects of neurohypophysectomy on urine
146
those of mammalian neurohypophysial peptides, as it exerted a far more potent
'water balance effect' (water retention) when injected into frogs . The activity in
the neurohypophysis of the grass snake was later (HELLER and PICKERING, 1961)
shown to be pharmacologically identical with 8-arg101Oe-oxytocin (vasotocin). A
second peptide, similar in its properties to mammalian oxytocin, was also found
in the grass snake. The caiman neurohypophysis was found to contain vasotocin,
but a second activity could not be identified in this species, though both were found
in the green turtle, Chelonia mydas (SAWYER, MUNSICK, and VAN DYKE, 1961). Vasotocins have since been identified in other groups (Table 5.6), including the snakes,
in which their structure has been confirmed by amino acid analysis (PICKERING,
1967; ACHER, CHAUVET, and CHAUVET, 1968). The second peptide activity that was
found initially in most of the reptiles examined has been pharmacologically identified as 8-ileu-oxytocin (mesotocin) in the rattlesnake (MUNSICK, 1966) and found
chemically to be such in the viper, cobra and elaph (ACHER et al., 1968; ACHER,
CHAUVET, and CHAUVET, 1969a). PICKERING (1967) found that amino acid analysis,
indicated both the presence of mesotocin and oxytocin in the neurohypophysis
of the cobra and FOLLETT (1967) has presented tentative pharmacological evidence
to suggest that this may also be so in other reptiles. ACHER et al. (1969 a) emphasize
that they are unable chemically to detect oxytocin in the viper, cobra or elaph. PICKERING also found an additional peptide, similar to vasotocin, in the cobra, but this
has not yet been exhaustively characterized. Few results indicating concentrations
of such peptides 10 reptiles are available, but in the grass snake the level of vasotocin
is about 4 - 9 X 10.
9
M kg body weight (calc. from HELLER and PICKERING, 1961;
FOLLETT, 1967), a value comparable with those in other tetrapods. There is usually
2 - 4 times as much vasotocin as the other active peptides.
Mammalian neurohypophysial peptide preparations have been shown to exert
an antidiuretic effect when injected into the alligator and into Trachysaurus rugosus
(Table 5.7). Extracts of reptilian neurohypophyses also exert such an action when
injected back into the contributing species . DANTZLER (1967 a) has made a careful
analysis of the actions of vasotocin, mesotocin and oxytocin on the renal function
of the water snake Natrix sipedon. All of these neurohypophysial peptides can produce an antidiuresis, but mesotocin and oxytocin are only effective in large doses
that are always associated with a reduced GFR and a decrease in blood pressure.
Vasotocin reduces urine flow in small doses that have no action on blood pressure
and acts both by reducing the GFR and by increasing tubular water reabsorption.
The renal tubular action of vasotocin has a lower dose-response threshold than
its glomerular effects . The results suggested that the decreased GFR was due to
a reduction in the number of active glomeruli. It is uncertain whether vasotocin
has this pattern of action throughout the Reptilia for, as we have seen, there is a
considerable diversity in the renal processes of this group. Injection of large
amounts of Pitressin into the alligator thus was found to reduce the GFR without
affecting tubular absorption but such experiments should be repeated using small
doses of vasotocin.
The evidence for a physiological role of neurohypophysial peptides in controlling urine flow in reptiles remains circumstantial, and less complete than in any
other tetrapod group. Unfortunately the effects of neurohypophysectomy on urine
146