mittency), rather than a change in ultrafiltration at individual sites. It seemed likely
that these effects were being mediated by a release of the neurohypophysial peptide
vasotocin, but infusion of this hormone at modest rates did not alter the GFR. urine flow in birds thus responds to changes in body hydration, and such processes
involve tubular water reabsorption and some changes in the GFR, though the physiological importance of the latter is not clear.
Neurohypophysectomy in the domestic fowl results in the formation of large
volumes of urine (SHIRLEY and NALBANDOV, 1956). A strain of chickens has
recently been identified that exhibits a genetic predisposition to form excessive
quantities of urine (DUNSON and Buss, 1968). Such birds drink three times the
normal volume of water (polydipsia), and secrete urine with an osmolarity of only
about 100 m-osmole/l, as compared to the more usual concentrations of 500 rnosmole/l . These chickens are reminiscent of the Brattleboro strain of laboratory
rats, which suffer from diabetes insipidus due to a lack of neurohypophysial antidiuretic hormone. At the time of writing such a deficiency has not been reported
in this strain of domestic fowl, though injection of neurohypophysial pep tides
brings about an increase in the urine concentration.
The injection of neurohypophysial peptides into the normal domestic fowl results in decreased secretion of urine. BURGESS, HARVEY, and MARSHALL (1933)
showed that 'Pitressin', derived from mammalian neurohypophyses, has such an
effect and that this is due to both an increased reabsorption of water from the renal
tubules and a decreased GFR. Pitressin also has an antidiuretic effect when injected
into the domestic duck (HOLMES and ADAMS, 1963). Birds, including the domestic
fowl and duck, store 8-arginine vasotocin and oxytocin (but not vasopressin) in
their neurohypophyses (see Table 4.1). When vasotocin is injected into hydrated
chickens it also produces an antidiuresis, while oxytocin has little effect in this respect (MUNSICK, SAWYER, and VAN DYKE, 1964). ERIK SKADHAUGE has carefully
analyzed the renal sites of action of vasotocin. Small amounts of this peptide were
injected into the renal portal vein of hydrated chickens and so made initial contact
with the renal tubules, instead of the glomeruli. The decreased urine flow, which
was observed, resulted from increased tubular reabsorption of water, with no measurable change in GFR or renal blood flow. Higher doses of vasotocin decreased
the GFR and renal blood flow but this effect is considered to be of pharmacological, rather than physiological, significance. Neurohypophysial peptides in large
doses decrease the blood pressure of the domestic fowl and a variety of other birds,
including pigeons (WARING, MORRIS, and STEPHENS, 1956), penguins, emus and
cormorants (WOOLLEY, 1959). Such a vascular action could mediate the decreased
GFR that is observed when large doses of such peptides are injected. The dose of
vasotocin that must be injected to produce a drop in the blood pressure of the domestic fowl is 10 to 20 times greater than that which has an antidiuretic effect (SKADHAUGE, 1969a). It seems likely that, under physiological conditions, vasotocin
changes the urine volume in the fowl by altering renal tubular water reabsorption.
The glomerulus may, however, respond in certain circumstances, especially as it
shows lability in its activity.
The preceding information about the presence of vasotocin, and its effects when
injected is only indirect evidence as to its role in the birds. Indeed
neurohypophysial peptides have not been demonstrated in the circulation follow117
that these effects were being mediated by a release of the neurohypophysial peptide
vasotocin, but infusion of this hormone at modest rates did not alter the GFR. urine flow in birds thus responds to changes in body hydration, and such processes
involve tubular water reabsorption and some changes in the GFR, though the physiological importance of the latter is not clear.
Neurohypophysectomy in the domestic fowl results in the formation of large
volumes of urine (SHIRLEY and NALBANDOV, 1956). A strain of chickens has
recently been identified that exhibits a genetic predisposition to form excessive
quantities of urine (DUNSON and Buss, 1968). Such birds drink three times the
normal volume of water (polydipsia), and secrete urine with an osmolarity of only
about 100 m-osmole/l, as compared to the more usual concentrations of 500 rnosmole/l . These chickens are reminiscent of the Brattleboro strain of laboratory
rats, which suffer from diabetes insipidus due to a lack of neurohypophysial antidiuretic hormone. At the time of writing such a deficiency has not been reported
in this strain of domestic fowl, though injection of neurohypophysial pep tides
brings about an increase in the urine concentration.
The injection of neurohypophysial peptides into the normal domestic fowl results in decreased secretion of urine. BURGESS, HARVEY, and MARSHALL (1933)
showed that 'Pitressin', derived from mammalian neurohypophyses, has such an
effect and that this is due to both an increased reabsorption of water from the renal
tubules and a decreased GFR. Pitressin also has an antidiuretic effect when injected
into the domestic duck (HOLMES and ADAMS, 1963). Birds, including the domestic
fowl and duck, store 8-arginine vasotocin and oxytocin (but not vasopressin) in
their neurohypophyses (see Table 4.1). When vasotocin is injected into hydrated
chickens it also produces an antidiuresis, while oxytocin has little effect in this respect (MUNSICK, SAWYER, and VAN DYKE, 1964). ERIK SKADHAUGE has carefully
analyzed the renal sites of action of vasotocin. Small amounts of this peptide were
injected into the renal portal vein of hydrated chickens and so made initial contact
with the renal tubules, instead of the glomeruli. The decreased urine flow, which
was observed, resulted from increased tubular reabsorption of water, with no measurable change in GFR or renal blood flow. Higher doses of vasotocin decreased
the GFR and renal blood flow but this effect is considered to be of pharmacological, rather than physiological, significance. Neurohypophysial peptides in large
doses decrease the blood pressure of the domestic fowl and a variety of other birds,
including pigeons (WARING, MORRIS, and STEPHENS, 1956), penguins, emus and
cormorants (WOOLLEY, 1959). Such a vascular action could mediate the decreased
GFR that is observed when large doses of such peptides are injected. The dose of
vasotocin that must be injected to produce a drop in the blood pressure of the domestic fowl is 10 to 20 times greater than that which has an antidiuretic effect (SKADHAUGE, 1969a). It seems likely that, under physiological conditions, vasotocin
changes the urine volume in the fowl by altering renal tubular water reabsorption.
The glomerulus may, however, respond in certain circumstances, especially as it
shows lability in its activity.
The preceding information about the presence of vasotocin, and its effects when
injected is only indirect evidence as to its role in the birds. Indeed
neurohypophysial peptides have not been demonstrated in the circulation follow117