Coturnix coturnix japonica, are deprived of water, or given 0.2 M saline solutions
to drink, the storage of vasotocin in the neural lobe is reduced by 80% and that
of oxytocin is decreased by 60%. These changes were correlated with parallel
decreases in the stainable neurosecretory materials in the neural lobe. Such histological changes, in response to dehydration or drinking saline solutions, have also
been shown in the domestic fowl (LEGAIT, 1959), the white-crowned sparrow and
the zebra finch (F ARNER and OKSCHE, 1962). It is interesting that the budgerygah,
which in some circumstances can survive for prolonged periods without drinking
water, does not exhibit depletion of neurosecretory material after 7 days without
water (UEMURA, 1964), a condition reminiscent of certain desert rodents.
Vasotocin is far more active than oxytocin in decreasing urine volume, and its
action in contracting the avian oviduct is similarly greater. The half life of oxytocin
in the circulation of chickens is about 9 min and that of vasotocin 13 min (HASAN
and HELLER, 1968). Vasotocin is usually present at a higher concentration than
oxytocin in the avian neurohypophysis (Table 4.1). Estimates of the total storage
of vasotocin are sparse, but are similar to those in mammals. (c.f. Table 3.1). The
single estimate of peptide storage in the gull, Larus canus, is especially high, and
it may reflect the magnitude of its osmotic problems, which are associated with
a marine environment. Comparison of such peptide storage in other species may
provide information relevant to the importance of these hormones in their natural
way of life.
2. Role of the Cloaca and Intestine in Water Conservation
Birds lack a urinary bladder; urine passes from the ureters into a posterior part
of the gut called the cloaca. Faeces and products of the urinogenital system all ultimately pass this way. Anatomically the posterior part of the gut consists of several
regions; the proctodaeum, urodaeum and coprodaeum that make up the cloaca .
The large intestine is in communication with the coprodaeum. SKADHAUGE (1968)
found traces of uric acid far up in the large intestine, and even in the ceca, of the
domestic fowl and duck. When dyes were placed in the proctodaeum they were subsequently also found in these regions. Radiographic contrast media are excreted
by the chicken kidney and x-ray examination has shown that within minutes of
passing out of the ureters they pass far up into the intestine (NECHAY, BOYARSKY,
and CATACUTAN-LABAY, 1968; AKESTER et al., 1967). Thus the cloaca and large
intestine of birds are in free communication, so that physiologically one cannot
separate osmotic events that occur in these two regions.
That changes in the water and electrolyte content of the ureteral urine occur
after it has passed into the cloaca has been considered likely for a long time, but
until recently has been more the subject of speculation than conclusive experiments.
The openings of the ureters can be transferred surgically to the exterior of the bird
so that the urine bypasses the cloaca. HART and ESSEX (1942) found that domestic
chickens with such a surgical rearrangement needed extra salt in their diet . More
recently DICKER and HASLAM (1966) have shown that such birds drink twice the
amount of water after such an operation. Both these observations could be due
to added urinary losses, such as could result from a failure to reabsorb water and
119
to drink, the storage of vasotocin in the neural lobe is reduced by 80% and that
of oxytocin is decreased by 60%. These changes were correlated with parallel
decreases in the stainable neurosecretory materials in the neural lobe. Such histological changes, in response to dehydration or drinking saline solutions, have also
been shown in the domestic fowl (LEGAIT, 1959), the white-crowned sparrow and
the zebra finch (F ARNER and OKSCHE, 1962). It is interesting that the budgerygah,
which in some circumstances can survive for prolonged periods without drinking
water, does not exhibit depletion of neurosecretory material after 7 days without
water (UEMURA, 1964), a condition reminiscent of certain desert rodents.
Vasotocin is far more active than oxytocin in decreasing urine volume, and its
action in contracting the avian oviduct is similarly greater. The half life of oxytocin
in the circulation of chickens is about 9 min and that of vasotocin 13 min (HASAN
and HELLER, 1968). Vasotocin is usually present at a higher concentration than
oxytocin in the avian neurohypophysis (Table 4.1). Estimates of the total storage
of vasotocin are sparse, but are similar to those in mammals. (c.f. Table 3.1). The
single estimate of peptide storage in the gull, Larus canus, is especially high, and
it may reflect the magnitude of its osmotic problems, which are associated with
a marine environment. Comparison of such peptide storage in other species may
provide information relevant to the importance of these hormones in their natural
way of life.
2. Role of the Cloaca and Intestine in Water Conservation
Birds lack a urinary bladder; urine passes from the ureters into a posterior part
of the gut called the cloaca. Faeces and products of the urinogenital system all ultimately pass this way. Anatomically the posterior part of the gut consists of several
regions; the proctodaeum, urodaeum and coprodaeum that make up the cloaca .
The large intestine is in communication with the coprodaeum. SKADHAUGE (1968)
found traces of uric acid far up in the large intestine, and even in the ceca, of the
domestic fowl and duck. When dyes were placed in the proctodaeum they were subsequently also found in these regions. Radiographic contrast media are excreted
by the chicken kidney and x-ray examination has shown that within minutes of
passing out of the ureters they pass far up into the intestine (NECHAY, BOYARSKY,
and CATACUTAN-LABAY, 1968; AKESTER et al., 1967). Thus the cloaca and large
intestine of birds are in free communication, so that physiologically one cannot
separate osmotic events that occur in these two regions.
That changes in the water and electrolyte content of the ureteral urine occur
after it has passed into the cloaca has been considered likely for a long time, but
until recently has been more the subject of speculation than conclusive experiments.
The openings of the ureters can be transferred surgically to the exterior of the bird
so that the urine bypasses the cloaca. HART and ESSEX (1942) found that domestic
chickens with such a surgical rearrangement needed extra salt in their diet . More
recently DICKER and HASLAM (1966) have shown that such birds drink twice the
amount of water after such an operation. Both these observations could be due
to added urinary losses, such as could result from a failure to reabsorb water and
119