gallinago, and the green sandpiper, Tringa glareola, that nasal glands weigh 0.1
to 0.3 mg per g body weight while in marine species, such as the herring gull, Larus
argentatus, and the little auk, Plautus aile, they weigh about 1 mg per g BW . These
differences probably reflect the level of extrarenal salt excretion which the birds
normally experience. Such marine species also have an enhanced ability to secrete
salt solutions from the nasal glands . These differences in nasal gland morphology
and function depend on both the genetic and dietary habits of the birds. Marine
birds possess larger nasal glands than terrestrial-freshwater species, irrespective of
the salt content of the diet, but the development of these glands is enhanced by
a high salt diet (SCHMIDT-NIELSEN and KIM, 1964).
The adrenocortical hormones can influence sodium excretion by the kidneys
and nasal glands, though their exact physiological role is not clear . When birds,
such as the domestic fowl or pigeon, are adrenalectomized they only survive for
two or three days, but this period can be extended by providing them with salt
solutions to drink, or injections of corticosteroids (PARKINS, 1931; MILLER and
RIDDLE, 1942). Ducks adrenalectomized by PHILLIPS, HOLMES, and BUTLER (1961)
suffered a decline in plasma sodium concentration but, in contrast to mammals,
no change in potassium levels. When these ducks were given saline solutions per
as, the sodium excretion and urine volumes were greater than in normal birds, or
in adrenalectomized ones which had been maintained with cortisol injections. This
suggests that corticosteroids enhance reabsorption of sodium from the avian renal
tubules, just as in mammals. Injection of corticosterone or cortisol into intact
ducks, decreased the renal excretion of sodium and decreased potassium levels in
the urine, the latter effect contrasting with its action in mammals.
a) Mechanism(s) Controlling Secretion . The mechanism(s) controlling secretion
from the nasal salt gland appear to be primarily nervous in origin, but are facilitated
by the action of adrenocortical steroids. KNUT SCHMIDT-NIELSEN and his collaborators (SCHMIDT-NIELSEN, JORGENSEN, and O SAKI, 1958; FANGE, SCHMIDTNIELSEN, and ROBINSON, 1958; SCHMIDT-NIELSEN and FANGE 1958) investigated
the process of nasal salt secretion in cormorants, herring gulls and brown pelicans,
and found that injection or ingestion of hypertonic solutions of sodium chloride
evoked secretion of fluid by the gland . Hyperosrnotic solutions of sucrose (which
lowered the plasma sodium concentration!) also increased secretion, indicating that
the primary stimulus is osmotic, rather than an elevated sodium concentration. This
has recently also been found to be so in ducks (ASH , 1969). When ducks are given
a saline load per as, there is an initial diuresis, lasting about one hour, during which
the nasal gland starts to secrete (HOLMES, PHILLIPS, and BUTLER, 1961); in ASH'S
experience the initiation varies from 7 to 25 min.
The spec ific physiological events that link the osmotic stimulus with the initiation of secretion involve a nervous reflex . SCHMIDT-NIELSEN'S group found that
when hyperosmotic solutions were administered to the herring gull, the commencement of secretion from the nasal gland could be prevented if the birds were
anaesthetized, suggesting that the osmoreceptors are located in the central nervous
system. It was also found that stimulation of the parasympathetic nerve supply
to the nasal glands , resulted in secretion of fluid within a minute and this reached
maximal levels in 5 to 10 min. The volume and composition of these fluids were
123
to 0.3 mg per g body weight while in marine species, such as the herring gull, Larus
argentatus, and the little auk, Plautus aile, they weigh about 1 mg per g BW . These
differences probably reflect the level of extrarenal salt excretion which the birds
normally experience. Such marine species also have an enhanced ability to secrete
salt solutions from the nasal glands . These differences in nasal gland morphology
and function depend on both the genetic and dietary habits of the birds. Marine
birds possess larger nasal glands than terrestrial-freshwater species, irrespective of
the salt content of the diet, but the development of these glands is enhanced by
a high salt diet (SCHMIDT-NIELSEN and KIM, 1964).
The adrenocortical hormones can influence sodium excretion by the kidneys
and nasal glands, though their exact physiological role is not clear . When birds,
such as the domestic fowl or pigeon, are adrenalectomized they only survive for
two or three days, but this period can be extended by providing them with salt
solutions to drink, or injections of corticosteroids (PARKINS, 1931; MILLER and
RIDDLE, 1942). Ducks adrenalectomized by PHILLIPS, HOLMES, and BUTLER (1961)
suffered a decline in plasma sodium concentration but, in contrast to mammals,
no change in potassium levels. When these ducks were given saline solutions per
as, the sodium excretion and urine volumes were greater than in normal birds, or
in adrenalectomized ones which had been maintained with cortisol injections. This
suggests that corticosteroids enhance reabsorption of sodium from the avian renal
tubules, just as in mammals. Injection of corticosterone or cortisol into intact
ducks, decreased the renal excretion of sodium and decreased potassium levels in
the urine, the latter effect contrasting with its action in mammals.
a) Mechanism(s) Controlling Secretion . The mechanism(s) controlling secretion
from the nasal salt gland appear to be primarily nervous in origin, but are facilitated
by the action of adrenocortical steroids. KNUT SCHMIDT-NIELSEN and his collaborators (SCHMIDT-NIELSEN, JORGENSEN, and O SAKI, 1958; FANGE, SCHMIDTNIELSEN, and ROBINSON, 1958; SCHMIDT-NIELSEN and FANGE 1958) investigated
the process of nasal salt secretion in cormorants, herring gulls and brown pelicans,
and found that injection or ingestion of hypertonic solutions of sodium chloride
evoked secretion of fluid by the gland . Hyperosrnotic solutions of sucrose (which
lowered the plasma sodium concentration!) also increased secretion, indicating that
the primary stimulus is osmotic, rather than an elevated sodium concentration. This
has recently also been found to be so in ducks (ASH , 1969). When ducks are given
a saline load per as, there is an initial diuresis, lasting about one hour, during which
the nasal gland starts to secrete (HOLMES, PHILLIPS, and BUTLER, 1961); in ASH'S
experience the initiation varies from 7 to 25 min.
The spec ific physiological events that link the osmotic stimulus with the initiation of secretion involve a nervous reflex . SCHMIDT-NIELSEN'S group found that
when hyperosmotic solutions were administered to the herring gull, the commencement of secretion from the nasal gland could be prevented if the birds were
anaesthetized, suggesting that the osmoreceptors are located in the central nervous
system. It was also found that stimulation of the parasympathetic nerve supply
to the nasal glands , resulted in secretion of fluid within a minute and this reached
maximal levels in 5 to 10 min. The volume and composition of these fluids were
123