with sea-water, this vasodilatation was accompanied by a cessation of chloride extrusion. As already noted, increases in ur ine flow (and renal sodium loss) resulting
from the inject ion of vasotocin are usually accompanied by an elevation in the
blood pressure. Adrenaline, angiotensin II, and extracts of eel urophyses and corpuscles of STANNIUS also have parallel actions on both processes (G-IESTERJONES
et al., 1969b). The role of vascular changes in the normal regulation of piscine kidney function is unknown, but the circulatory supply to this gland is complex as
it usuall y has both a venous renal portal (tubular) and an arterial (glomerular) sup -
ply . The kidneys of fish also can exhibit the phenomenon of 'glomerular recruitment' which suggests a lability in their vascular arrangements. Recently more information has become available on the pattern of circulation in the gills in which
different regions are supplied by distinct blood vessels . The blood supply to the
(respiratory) gill lamellae is increased by the action of adrenaline while that to the
intermediate regions between these structures ('central compartments') is boosted
by large doses of acetylcholine (STEEN and KRUYSSE, 1964; RICHARDS and FROMM,
1969). MAETZ and RANKIN (1969) found that small doses of vasotocin and isotocin
have an effect similar to that of acetylcholine on the gills of eels. The 'chloride secreting cells' are situated at the base of the gill lamellae and are supplied by blood
flowing through the 'central compartments'. Thus, in the presence of adrenaline,
the y have a reduced blood supply consistent with the cessation of their activity.
Vasotocin, on the other hand, increases their blood supply and this may be the
reason for the facilitated rate of branchial sodium exchange which is seen in the
presence of such peptides (MAETZ and RANKIN, 1969). The concentrations of the
neurohypophysial peptides required to elicit changes in the blood supply to the
gills are 109
to 1011
M for vasotocin and as little as 1013
M for isotocin. There
is no information available about the presence of such pep tides in fish blood, but
in mammals and amphibians their concentration is about 1010 to 1011
M. The
effective levels of adrenaline are comparable with those known to be present in
the blood of fish (FONTAINE, MAZEAUD, and MAZEAUD, 1963). Whether such vasoactive substances normally have a role to play in osmoregulation is unknown
but the blood pressure of eels is quite labile . When, for instance, these fish are transferred from sea-water to fresh water the blood pressure increases (CHESTER JONES
et al ., 1969 a). If this reflects a release of adrenaline, such a hormone could produce
a reduced secretion from the ' chloride secreting cells' and a facilitated water excretion by the kidney. On the other hand, if vasotocin were released in sea-water
it would have the opposite effect on salt loss, stimulating its secretion from the
gills. However, if present in sufficient quantities it would, like adrenaline, also be
expected to increase the blood pressure and renal water loss. The potential actions
of these hormones and the observed physiological responses of the fish in sea and
fresh water thus cannot always be reconciled. The poss ibilities are, however, interesting and will no doubt be the object of further research.
I have recently attempted to demonstrate the presence of vasotocin in the blood
of the North American eel, Anguilla rostrata (BENTLEY, 1971 b). The limits of sensitivity of the assay (toad urinary bladder) were 1011 M (in eels blood). The concentrations required to alter the branchial blood flow, increase the blood pressure
and promote a diuresis in European eels are usually greater than this. However,
when the fish were transferred from fresh to sea-water, sea to fresh water or sub243
from the inject ion of vasotocin are usually accompanied by an elevation in the
blood pressure. Adrenaline, angiotensin II, and extracts of eel urophyses and corpuscles of STANNIUS also have parallel actions on both processes (G-IESTERJONES
et al., 1969b). The role of vascular changes in the normal regulation of piscine kidney function is unknown, but the circulatory supply to this gland is complex as
it usuall y has both a venous renal portal (tubular) and an arterial (glomerular) sup -
ply . The kidneys of fish also can exhibit the phenomenon of 'glomerular recruitment' which suggests a lability in their vascular arrangements. Recently more information has become available on the pattern of circulation in the gills in which
different regions are supplied by distinct blood vessels . The blood supply to the
(respiratory) gill lamellae is increased by the action of adrenaline while that to the
intermediate regions between these structures ('central compartments') is boosted
by large doses of acetylcholine (STEEN and KRUYSSE, 1964; RICHARDS and FROMM,
1969). MAETZ and RANKIN (1969) found that small doses of vasotocin and isotocin
have an effect similar to that of acetylcholine on the gills of eels. The 'chloride secreting cells' are situated at the base of the gill lamellae and are supplied by blood
flowing through the 'central compartments'. Thus, in the presence of adrenaline,
the y have a reduced blood supply consistent with the cessation of their activity.
Vasotocin, on the other hand, increases their blood supply and this may be the
reason for the facilitated rate of branchial sodium exchange which is seen in the
presence of such peptides (MAETZ and RANKIN, 1969). The concentrations of the
neurohypophysial peptides required to elicit changes in the blood supply to the
gills are 109
to 1011
M for vasotocin and as little as 1013
M for isotocin. There
is no information available about the presence of such pep tides in fish blood, but
in mammals and amphibians their concentration is about 1010 to 1011
M. The
effective levels of adrenaline are comparable with those known to be present in
the blood of fish (FONTAINE, MAZEAUD, and MAZEAUD, 1963). Whether such vasoactive substances normally have a role to play in osmoregulation is unknown
but the blood pressure of eels is quite labile . When, for instance, these fish are transferred from sea-water to fresh water the blood pressure increases (CHESTER JONES
et al ., 1969 a). If this reflects a release of adrenaline, such a hormone could produce
a reduced secretion from the ' chloride secreting cells' and a facilitated water excretion by the kidney. On the other hand, if vasotocin were released in sea-water
it would have the opposite effect on salt loss, stimulating its secretion from the
gills. However, if present in sufficient quantities it would, like adrenaline, also be
expected to increase the blood pressure and renal water loss. The potential actions
of these hormones and the observed physiological responses of the fish in sea and
fresh water thus cannot always be reconciled. The poss ibilities are, however, interesting and will no doubt be the object of further research.
I have recently attempted to demonstrate the presence of vasotocin in the blood
of the North American eel, Anguilla rostrata (BENTLEY, 1971 b). The limits of sensitivity of the assay (toad urinary bladder) were 1011 M (in eels blood). The concentrations required to alter the branchial blood flow, increase the blood pressure
and promote a diuresis in European eels are usually greater than this. However,
when the fish were transferred from fresh to sea-water, sea to fresh water or sub243