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Adrenalectomy fails to block solute-free water conservation by the nasal glands of salt-adapted pekin ducks (Anas platyrhynchos)
Camp. Biochem. Physiol. Vol. 8bA, No. 3, pp. 397-401, Printed in Great Britain
03~-9629/87 Pergamon
1987
$3.00 + 0.00 Journals Ltd
ADRENALECTO~Y FAILS TO BLOCK SOLUTE-FREE WATER CONSERVATION BY THE NASAL GLANDS OF SALT-ADAPTED PEKIN DUCKS (ANAS
PLATYRHYNCHOS)
DAVID GORDONBUTLER Department of Zoology, University of Toronto, Toronto, Ontario, Canada M5S IA1 (Received 7 April 1986) Abstract-l. One week after adrenalectomy, the total output of fluid and osmolytes by the nasal salt glands were 82 and 84% of the respective outputs by sham-adrenalectomized controls. 2. Three days after adrenalectomy, the total volume of solute-free water gained by the nasal salt glands was 77% of that gained by the sham-adrenal~tomiz~ controls; after 7 days it was 80%. Two weeks after adrenalectomy, the ducks lost some of their strength and the total volume decreased to 65%. 3. It was concluded that the primary secretion of NaCl and the conservation of solute-free water by the nasal salt glands are not regulated primarily by adrenocortical steroids.
ea al., 1961; Holmes, 1972; Thomas 1978; Holmes and Phillips, 1985).
INTRODUaION Avian nasal salt glands are crescent-shaped structures located in depressions in the skull above each eye. Their size in aquatic birds is functionally related to environmental salinity (Holmes et al., 1961). Each gland is composed of radially arranged secretory tubules which are supplied with a counter-current arterial blood flow. Secretory tubules produce a highly concentrated solution of NaCl with traces of K+, -HCO,, Ca’+ and Mg’+. They empty into a series of central canals which run in parallel and unite to form a single duct which empties near the external nare. The Na+ transporting mechanism is not fully understood and may be part of a single stage or a two-stage process (see review, Holmes and Phillips, 1985). In the single-stage process Cl- may be transported actively via the basal membrane into the secretory cell (Ernst and Van Rossum, 1982). Na+ follows passively and is then actively transported across the basolateral membranes and into the intercellular spaces (Ernst and Mills, 1977) in exchange for K+. Apical ~rmeability increases favouring the diffusion of Cl- from the cell, into the tubular lumen (Ernst et al., 1980). The two-stage hypothesis proposes that an isotonic fluid is secreted by the peripheral tubular cells. It then flows over the principal cells lining the length of the secretory tubule. Water is drawn out of the tubular lumen via the leaky junctions between these cells and into the intercellular space which contains a standing osmotic gradient of Nat (Diamond and Tormey, 1966). This gradient is established and maintained by Na+ pumps located on the basolateral membranes of the principal cells (Ellis et al., 1977).
By secreting a concentrated solution of NaCl in response to an elevated plasma osmotic concentration, bird nasal salt glands extract solute-free water (Butler, 1985c). In the present experiment I have tested the hypothesis that NaCl secretion by the principal cells of the duck salt glands is regulated by adrenocortical steroids (Holmes et al., 1961; Phillips C.BP.W3/--4
MATERIALSAND
and Phillips,
METHODS
Seven week-old Pekin drakes weighing approximately 3 kg were purchased from King Cole Duck Farms, Aurora, Ontario and held indoors under a photoperiod of 12L: 12D. They were fed 0.9% NaCl drinking water and commercial duck grower food for 1 month before they were used for experiments. Experimenial procedure
Nasal salt gland function was observed in six shamoperated and seven adrenalectomized (Butler, 1980, 1985b) ducks 3, 7 and 14 days after surgery. During this ICday Period, the ducks were force-fed daily with 2OOml of a mixture of duck grower food and 0.9% NaCl and given solid food and 0.9% NaCl drinking water ad fibitum. Each duck was tied, in the prone position, to a holding board. If movement and noise were kept to a minimum, the duck remained calm throughout the entire observation period. Blood (3 ml) was withdrawn via an indwelling cannula (PE 60) in the left ulnar vein. Plasma was stored at -40°C. Next, 45ml of OSM NaCl was injected via an indwelling cannula in the right ulnar vein. The nasal salt glands usually began to secrete fluid within about 3 min and continued to secrete for more than 1 hr. When fluid secretion stopped, a 1000 mOsm/kg solution of NaCl waslnfused into the right ulnar vein at a rate of 0.98 ml/min for 90 min. The nasal salt glands started to secrete less then 2 min after this infusion was started. At this point, a second 3 ml blood sample was cotlected via the left ulnar cannula. Nasal fluid samples were collected for S-min intervals during the entire 90”min period of infusion, each sample being withdrawn into a preweighed 5 ml plastic syringe. The volume of nasal fluid was then determined by difference in weight. Nasal fluid samples, as well as plasma samples, were stored at -40°C. Osmolal concentrations were later measured by freezing point depression with a Fiske Osmometer (Advanced Instruments Ltd.). Calculation of osmolal and free water clearance
The rate of osmolal clearance (C,,,) is the rate (ml/kg bw per 5 min period) at which all of the osmotically active solutes are extracted or cleared from the plasma by the nasal
397
DAVID GORDON
398
BUTLER
attempt to counter-balance the renalLcloaca1 loss of electrolytes and water which would otherwise lead to co,, = NF,,, X ‘NF a decrease in arterial blood pressure, an increase in Posm cardiac frequency and a 50% reduction in stroke where NF_ is the nasal fluid osmolality (mOsm/kg water); volume (Butler, 1985b). This strategy was successful V,, is the nasal fluid volume (ml/kg bw per 5 min period); insofar as nasal fluid secretion rates were almost (mOsm/kg water). Free and PO,, is the plasma osmolality normaf during the first week after adrenalectomy clearance (CnIo) is the rate at which osmotically free water (Fig. 1). Even 2 weeks after adrenalectomy, arterial is gained or lost by the nasal salt glands or blood pressure remained elevated (Butler, 1986) and c H>o--V NF - co,m~ the total output of nasal fluid amounted to about 65% of that secreted by the sham-operated controls When the free water clearance is negative, solute-free water is gained by the animal. (Figs 1 and 3). Nasai fluid osmolal concentrations tended to inTotal output of osmolyres, fluid and the gain of solute-free crease when the rate of nasal ffuid secretion decreased water (Fig. 1) although this change was not statistically Total volumes for each of the 18 successive, 5min significant. Thus, the rates of osmolyte secretion in collection periods were added to obtain the total volume adrenalectomized ducks were closer to those in the secreted by each duck. These within-group totals were used sham-operated controls; there being little evidence to calculate the mean value + SE. The same procedure was that adrenocortical steroids are fundamentally imused to calculate the total output of osmolytes and the total portant in active Na+ or Cl- transport. gain of solute-free water. Osmolal clearance was calculated as the number of ml (per kg bw per 5-min period) of plasma cleared of RESULTS AND DISCUSSION osmotically active solutes in order to yield the total Ducks were fed 0.9% NaCl drinking water for 1 number of mmoles of osmolytes in a given nasal fluid month before, and 14 days after, adrenalectomy in an sample (ml/kg bw per 5-min period, Fig. 2). salt glands
or
DUCK SALT GLAND SECRETION
I
AFTER
ADRENALECTOMY L1
SHAM
“=6
2X
ADx
flz7
Fig. I. Effect of adrenalectomy on nasal fluid osmolahty and the rates of fluid and osmoial secretion 3, 7 and 14 days after surgery. The nasal salt glands were observed during a 90-min i.v. infusion of 1000 mOsm/kg NaCl at a rate of 0.98 ml/min. Each value is the mean *SE for a given 5-min collection period. SHAM = sham-adrenalectomized controls; ADX = bilateral surgical adrenalectomy. Note that for ADX 14 days, n = 5.
Control of nasal gland secretion
399
DUCK SALT GLAND OSMOLAL AND FREE WATER CLEARANCE AFTER ADRENALECTOMY
El
SHAM
n=e
a
ADX
n=7
-4.0
2 P ::
-3.0
3 8 0"
-2.0
-1.0 0 -3.0
a y" 2 J "
0 ;
-2.0
-1.0
0 0
30
so 0
60
60
30 lnfuslon
900
30
80
90
period (mln)
Fig. 2. Effect of adrenalectomy on nasal fluid osmolal clearance and negative free water clearance, 3, 7 and 14 days after surgery. The nasal salt glands were observed during a 90-min i.v. infusion of 1000 mOsm/kg NaCl at a rate of 0.98 ml/min. Each value is the mean + SE for a given 5-min collection period. SHAM = sham-adrenalectomized controls; ADX = bilateral surgical adrenalectomy. Note that for ADX 14 days, n = 5. Free water conservation by duck nasal salt glands has been observed already.using a different experimental protocol (Butler, 1985~). In these earlier experiments, ducks were given freshwater to drink during the month before adrenalectomy and 0.9% NaCl afterwards. They were not force-fed after surgery. Salt gland activity was observed following a single iv. injection of 15 ml of 0.5 M NaCl. In the present experiment, the ducks were given an i.v. load of 0.5 M NaCl but the salt glands were observed during the subsequent 90-min infusion of 1~mOsm~kg NaCl at a rate of 0.98 ml/min. In the earlier experiments (Butler, 1985~) the rate of nasal fluid secretion
The rate of free water clearance was negative for both adrenalectomized and sham-adrenalectomized ducks (Fig. 2) showing that, during each 5-min collection there is a net gain of solute-free water. There was a slight reduction the rate of negative free water clearance during the first week after adrenalectomy (Fig. 2). It decreased further after 2 weeks. Figure 3 shows that, 3 days after adrenalectomy, the total amount of free water gained during the 90-min infusion period was 77% of that gained by the sham-operated controls; 7 days after adrenalectomy, it was 80%. Two weeks after adrenalectomy the amount totalled 65%.
Table I. Plasma osmolal concentrations (mOsm/kg water) at the onset of nasal fluid secretion by Pekin ducks (Anas ~fa~~r~y~c~o~) observed 3, 7 and 14 days after surgid adrenalectomy 3 Days resting
c
14 Days
7 Days onset
onset
resting
resting
onset
-PP__I-Shamadrenalectomy
Adrenalectomy
b
301.0 2.9
2
+
299.3 2.0
2
1
Values are means + SE.
318.8
2
4.4
316.8 3.1
314.6
300.5 z.
2.2
z
4.0
334.8 -,
320.5
302.0 i
b.0
2
5.4
304.3 2
318.5
3.3
3.3
1.
n:5
5.5
318.9 2
4.4
n=5
400 (6)
20 1
(7)
I
FUNCTIONAL
[6) (7)
(61 (51
T
_T
7
DAYS
I
HYPERTROPHY
1I
3
OF NASAL
AFTER
14
SURGERY
Fig. 3. Effect of adrenalectomy on the total output of fluid, osmolytes and the gain of osmotically free water by the nasal salt glands, 3, 7 and 14 days after surgery. The nasal salt glands were observed during a 90-min i.v. infusion of 1000 mOsm/kg NaCl at a rate of 0.98 ml/min. Values for each of the 18 successive 5-min collections were added to obtain the total for each duck. These totals were then used to calculate the meanISE shown on the histogram. SHAM = sham-adrenale~tomiz~ controls; ADX = bilateral surgical adrenafectomy. Note that for ADX I4 days, n = 5. SALT GLANDS
IN ADRENALECTOMIZED
DUCKS
SHAM
B a al-l.0
T s2_ if
(41
-
-0.8
2
DAYS SALINE
7 DAYS
2
DAYS SALINE
7
DAYS
2
DAYS
7
DAYS
SALINE
Fig. 4. From Butler (1985~). Effect of adrenalectomy on nasal fluid osmolality, the rate of fluid secretion and the rate of negative free water clearance 2, and 7 days after surgical adrenalectomy. These ducks were pre-adapted to fresh water and then transferred to 0.9% NaCl drinking water after surgery. The nasal salt ghtnds were activated with a single i.v. load of 45 ml of 0.5 M NaCi. Fluid was collected from the onset of secretion until the glands stopped secreting. Volumes and osmotic concentrations were recorded for each of the successive 5-min collection periods over the total period of secretion. These values were averaged and the mean value for each duck used to calculate the group mean+ SE as shown in the histogram. SHAM = sham-adrenalectomized controls; ADX = bilateral surgical adrenalectomy.
Control of nasal gland secretion
doubled during the first week of exposure to 0.9% NaCl drinking water (Fig. 4), this functional hypertrophy being evident in both adrenalectomized ducks and sham-operated controls (Butler, 1985c). The rate of gain of osmotically free water also doubled in both experimental groups and therefore did not depend on stimulation by adrenocortical steroids (Fig. 4). Oceanic and brackish water birds secrete salt and
conserve osmotically free water with their nasal salt elands because their kidnevs are unable to form a hypertonic urine. Adrenocortical steroids will increase significantly the renalcloaca reabsorption of NaCl during adaptation to fresh water (Holmes and Adams, 1963). They are not, however, required for the functional hypertrophy that follows exposure to saline (Butler, 1980; 1985c) or for the basic level of NaCl secretion by the principal secretory cells of the avian nasal glands (Butler, 1980, 1984, 1985a,b).
gland secretion in Pekin ducks (Anus pluryrhynchos) adapted to 0.9% saline drinking water. Gen. camp. Endocr. (in press).
Diamond J. M. and Tormey J. M. (1966) Role of long extracellular channels in fluid transport across epithelia. Nature, Lond. 210, 817-820. Ellis R. A., Goertemiller C. C. and Stetson D. L. (1977) Significance of extensive leaky cell junctions in avian salt gland. Naiure, Lond. 268, 555-556. Ernst S. A. and Mills J. W. (1977) Basolateral plasma membrane localization of ouabain sensitive sodium transport sites in secretory epithelium of avian salt gland. J. Cell. Biol. 75, 7479.
Ernst S. A. and van Rossum G. D. V. (1982) Ions and energy metabolism in duck salt gland. J. Physiol. 325, 333-352.
Harvey S. and Phillips J. G. (1982) Endocrinology of salt gland function. Comp. Biochem. Physiol. 71, 537-546. Holmes W. N. (1972) Regulation of electrolyte balance in marine birds with special reference to the role of the pituitary-adrenal axis in the duck (Anus plutyrhynchos). Fedn Proc. fedn Am. Sots exp. Biol. 31, 1587-1597.
REFERENCES Butler D. G. (1980) Functional nasal salt glands in adrenalectomized domestic ducks (Anus plafyrhynchos). Gen. Comp. Endocrinol. 40, 15-26.
Butler D. G. (1984) Endocrine control of the nasal salt glands in birds. J. exp. Zool. 232, 725-736. Butler D. G. (1985a) Adrenalectomy blocks the circulatory and secretory responses by duck nasal salt glands to a hypertonic saline load. Comp. Biochem. Physiol. 81, 487490.
Butler D. G. (1985b) Cardiovascular function in adrenalectomized Pekin ducks (Anus pluryrhynchos). Comp. Biochem. Physiol. 81, 353-358. Butler D. G. (1985~) Free-water clearance by the nasal salt glands of adrenaLectomized ducks (Anus &tyrhynchos). Can. J. Zool. 63, 1213-1215.
Butler D. G. (1987) Adrenalectomy
401
fails to block salt
Holmes W. N. and Adams B. M. (1963) Effects of adrenocortical and neuro-hypophysial hormones on the renal excretory pattern of the water-loaded duck (Anus plutyrhynchos). Endocrinology 73, 5-10.
Holmes W. N., Butler D. G. and Philhps J. G. (1961) Observations on the effects of maintaining glaucouswinged gulls (Larus gluucescens) on freshwater and sea water for long periods. J. Endow. 23, 53-61. Holmes W. N. and Phillips J. G. (1985) The avian salt gland. Biol. Rev. 60, 213-256.
Phillips J. G., Holmes W. N. and Butler D. G. (1961) The effect of total and subtotal adrenalectomy on the renal and extrarenal responses of the domestic duck (Anas plutyrhynchos) to saline loading. Endocrinology, 69, 958-969.
Thomas D. H. and Phillips J. G. (1978) The anatomy and physiology of the avian nasal glands. Puuo 16, 89-104.
03~-9629/87 Pergamon
1987
$3.00 + 0.00 Journals Ltd
ADRENALECTO~Y FAILS TO BLOCK SOLUTE-FREE WATER CONSERVATION BY THE NASAL GLANDS OF SALT-ADAPTED PEKIN DUCKS (ANAS
PLATYRHYNCHOS)
DAVID GORDONBUTLER Department of Zoology, University of Toronto, Toronto, Ontario, Canada M5S IA1 (Received 7 April 1986) Abstract-l. One week after adrenalectomy, the total output of fluid and osmolytes by the nasal salt glands were 82 and 84% of the respective outputs by sham-adrenalectomized controls. 2. Three days after adrenalectomy, the total volume of solute-free water gained by the nasal salt glands was 77% of that gained by the sham-adrenal~tomiz~ controls; after 7 days it was 80%. Two weeks after adrenalectomy, the ducks lost some of their strength and the total volume decreased to 65%. 3. It was concluded that the primary secretion of NaCl and the conservation of solute-free water by the nasal salt glands are not regulated primarily by adrenocortical steroids.
ea al., 1961; Holmes, 1972; Thomas 1978; Holmes and Phillips, 1985).
INTRODUaION Avian nasal salt glands are crescent-shaped structures located in depressions in the skull above each eye. Their size in aquatic birds is functionally related to environmental salinity (Holmes et al., 1961). Each gland is composed of radially arranged secretory tubules which are supplied with a counter-current arterial blood flow. Secretory tubules produce a highly concentrated solution of NaCl with traces of K+, -HCO,, Ca’+ and Mg’+. They empty into a series of central canals which run in parallel and unite to form a single duct which empties near the external nare. The Na+ transporting mechanism is not fully understood and may be part of a single stage or a two-stage process (see review, Holmes and Phillips, 1985). In the single-stage process Cl- may be transported actively via the basal membrane into the secretory cell (Ernst and Van Rossum, 1982). Na+ follows passively and is then actively transported across the basolateral membranes and into the intercellular spaces (Ernst and Mills, 1977) in exchange for K+. Apical ~rmeability increases favouring the diffusion of Cl- from the cell, into the tubular lumen (Ernst et al., 1980). The two-stage hypothesis proposes that an isotonic fluid is secreted by the peripheral tubular cells. It then flows over the principal cells lining the length of the secretory tubule. Water is drawn out of the tubular lumen via the leaky junctions between these cells and into the intercellular space which contains a standing osmotic gradient of Nat (Diamond and Tormey, 1966). This gradient is established and maintained by Na+ pumps located on the basolateral membranes of the principal cells (Ellis et al., 1977).
By secreting a concentrated solution of NaCl in response to an elevated plasma osmotic concentration, bird nasal salt glands extract solute-free water (Butler, 1985c). In the present experiment I have tested the hypothesis that NaCl secretion by the principal cells of the duck salt glands is regulated by adrenocortical steroids (Holmes et al., 1961; Phillips C.BP.W3/--4
MATERIALSAND
and Phillips,
METHODS
Seven week-old Pekin drakes weighing approximately 3 kg were purchased from King Cole Duck Farms, Aurora, Ontario and held indoors under a photoperiod of 12L: 12D. They were fed 0.9% NaCl drinking water and commercial duck grower food for 1 month before they were used for experiments. Experimenial procedure
Nasal salt gland function was observed in six shamoperated and seven adrenalectomized (Butler, 1980, 1985b) ducks 3, 7 and 14 days after surgery. During this ICday Period, the ducks were force-fed daily with 2OOml of a mixture of duck grower food and 0.9% NaCl and given solid food and 0.9% NaCl drinking water ad fibitum. Each duck was tied, in the prone position, to a holding board. If movement and noise were kept to a minimum, the duck remained calm throughout the entire observation period. Blood (3 ml) was withdrawn via an indwelling cannula (PE 60) in the left ulnar vein. Plasma was stored at -40°C. Next, 45ml of OSM NaCl was injected via an indwelling cannula in the right ulnar vein. The nasal salt glands usually began to secrete fluid within about 3 min and continued to secrete for more than 1 hr. When fluid secretion stopped, a 1000 mOsm/kg solution of NaCl waslnfused into the right ulnar vein at a rate of 0.98 ml/min for 90 min. The nasal salt glands started to secrete less then 2 min after this infusion was started. At this point, a second 3 ml blood sample was cotlected via the left ulnar cannula. Nasal fluid samples were collected for S-min intervals during the entire 90”min period of infusion, each sample being withdrawn into a preweighed 5 ml plastic syringe. The volume of nasal fluid was then determined by difference in weight. Nasal fluid samples, as well as plasma samples, were stored at -40°C. Osmolal concentrations were later measured by freezing point depression with a Fiske Osmometer (Advanced Instruments Ltd.). Calculation of osmolal and free water clearance
The rate of osmolal clearance (C,,,) is the rate (ml/kg bw per 5 min period) at which all of the osmotically active solutes are extracted or cleared from the plasma by the nasal
397
DAVID GORDON
398
BUTLER
attempt to counter-balance the renalLcloaca1 loss of electrolytes and water which would otherwise lead to co,, = NF,,, X ‘NF a decrease in arterial blood pressure, an increase in Posm cardiac frequency and a 50% reduction in stroke where NF_ is the nasal fluid osmolality (mOsm/kg water); volume (Butler, 1985b). This strategy was successful V,, is the nasal fluid volume (ml/kg bw per 5 min period); insofar as nasal fluid secretion rates were almost (mOsm/kg water). Free and PO,, is the plasma osmolality normaf during the first week after adrenalectomy clearance (CnIo) is the rate at which osmotically free water (Fig. 1). Even 2 weeks after adrenalectomy, arterial is gained or lost by the nasal salt glands or blood pressure remained elevated (Butler, 1986) and c H>o--V NF - co,m~ the total output of nasal fluid amounted to about 65% of that secreted by the sham-operated controls When the free water clearance is negative, solute-free water is gained by the animal. (Figs 1 and 3). Nasai fluid osmolal concentrations tended to inTotal output of osmolyres, fluid and the gain of solute-free crease when the rate of nasal ffuid secretion decreased water (Fig. 1) although this change was not statistically Total volumes for each of the 18 successive, 5min significant. Thus, the rates of osmolyte secretion in collection periods were added to obtain the total volume adrenalectomized ducks were closer to those in the secreted by each duck. These within-group totals were used sham-operated controls; there being little evidence to calculate the mean value + SE. The same procedure was that adrenocortical steroids are fundamentally imused to calculate the total output of osmolytes and the total portant in active Na+ or Cl- transport. gain of solute-free water. Osmolal clearance was calculated as the number of ml (per kg bw per 5-min period) of plasma cleared of RESULTS AND DISCUSSION osmotically active solutes in order to yield the total Ducks were fed 0.9% NaCl drinking water for 1 number of mmoles of osmolytes in a given nasal fluid month before, and 14 days after, adrenalectomy in an sample (ml/kg bw per 5-min period, Fig. 2). salt glands
or
DUCK SALT GLAND SECRETION
I
AFTER
ADRENALECTOMY L1
SHAM
“=6
2X
ADx
flz7
Fig. I. Effect of adrenalectomy on nasal fluid osmolahty and the rates of fluid and osmoial secretion 3, 7 and 14 days after surgery. The nasal salt glands were observed during a 90-min i.v. infusion of 1000 mOsm/kg NaCl at a rate of 0.98 ml/min. Each value is the mean *SE for a given 5-min collection period. SHAM = sham-adrenalectomized controls; ADX = bilateral surgical adrenalectomy. Note that for ADX 14 days, n = 5.
Control of nasal gland secretion
399
DUCK SALT GLAND OSMOLAL AND FREE WATER CLEARANCE AFTER ADRENALECTOMY
El
SHAM
n=e
a
ADX
n=7
-4.0
2 P ::
-3.0
3 8 0"
-2.0
-1.0 0 -3.0
a y" 2 J "
0 ;
-2.0
-1.0
0 0
30
so 0
60
60
30 lnfuslon
900
30
80
90
period (mln)
Fig. 2. Effect of adrenalectomy on nasal fluid osmolal clearance and negative free water clearance, 3, 7 and 14 days after surgery. The nasal salt glands were observed during a 90-min i.v. infusion of 1000 mOsm/kg NaCl at a rate of 0.98 ml/min. Each value is the mean + SE for a given 5-min collection period. SHAM = sham-adrenalectomized controls; ADX = bilateral surgical adrenalectomy. Note that for ADX 14 days, n = 5. Free water conservation by duck nasal salt glands has been observed already.using a different experimental protocol (Butler, 1985~). In these earlier experiments, ducks were given freshwater to drink during the month before adrenalectomy and 0.9% NaCl afterwards. They were not force-fed after surgery. Salt gland activity was observed following a single iv. injection of 15 ml of 0.5 M NaCl. In the present experiment, the ducks were given an i.v. load of 0.5 M NaCl but the salt glands were observed during the subsequent 90-min infusion of 1~mOsm~kg NaCl at a rate of 0.98 ml/min. In the earlier experiments (Butler, 1985~) the rate of nasal fluid secretion
The rate of free water clearance was negative for both adrenalectomized and sham-adrenalectomized ducks (Fig. 2) showing that, during each 5-min collection there is a net gain of solute-free water. There was a slight reduction the rate of negative free water clearance during the first week after adrenalectomy (Fig. 2). It decreased further after 2 weeks. Figure 3 shows that, 3 days after adrenalectomy, the total amount of free water gained during the 90-min infusion period was 77% of that gained by the sham-operated controls; 7 days after adrenalectomy, it was 80%. Two weeks after adrenalectomy the amount totalled 65%.
Table I. Plasma osmolal concentrations (mOsm/kg water) at the onset of nasal fluid secretion by Pekin ducks (Anas ~fa~~r~y~c~o~) observed 3, 7 and 14 days after surgid adrenalectomy 3 Days resting
c
14 Days
7 Days onset
onset
resting
resting
onset
-PP__I-Shamadrenalectomy
Adrenalectomy
b
301.0 2.9
2
+
299.3 2.0
2
1
Values are means + SE.
318.8
2
4.4
316.8 3.1
314.6
300.5 z.
2.2
z
4.0
334.8 -,
320.5
302.0 i
b.0
2
5.4
304.3 2
318.5
3.3
3.3
1.
n:5
5.5
318.9 2
4.4
n=5
400 (6)
20 1
(7)
I
FUNCTIONAL
[6) (7)
(61 (51
T
_T
7
DAYS
I
HYPERTROPHY
1I
3
OF NASAL
AFTER
14
SURGERY
Fig. 3. Effect of adrenalectomy on the total output of fluid, osmolytes and the gain of osmotically free water by the nasal salt glands, 3, 7 and 14 days after surgery. The nasal salt glands were observed during a 90-min i.v. infusion of 1000 mOsm/kg NaCl at a rate of 0.98 ml/min. Values for each of the 18 successive 5-min collections were added to obtain the total for each duck. These totals were then used to calculate the meanISE shown on the histogram. SHAM = sham-adrenale~tomiz~ controls; ADX = bilateral surgical adrenafectomy. Note that for ADX I4 days, n = 5. SALT GLANDS
IN ADRENALECTOMIZED
DUCKS
SHAM
B a al-l.0
T s2_ if
(41
-
-0.8
2
DAYS SALINE
7 DAYS
2
DAYS SALINE
7
DAYS
2
DAYS
7
DAYS
SALINE
Fig. 4. From Butler (1985~). Effect of adrenalectomy on nasal fluid osmolality, the rate of fluid secretion and the rate of negative free water clearance 2, and 7 days after surgical adrenalectomy. These ducks were pre-adapted to fresh water and then transferred to 0.9% NaCl drinking water after surgery. The nasal salt ghtnds were activated with a single i.v. load of 45 ml of 0.5 M NaCi. Fluid was collected from the onset of secretion until the glands stopped secreting. Volumes and osmotic concentrations were recorded for each of the successive 5-min collection periods over the total period of secretion. These values were averaged and the mean value for each duck used to calculate the group mean+ SE as shown in the histogram. SHAM = sham-adrenalectomized controls; ADX = bilateral surgical adrenalectomy.
Control of nasal gland secretion
doubled during the first week of exposure to 0.9% NaCl drinking water (Fig. 4), this functional hypertrophy being evident in both adrenalectomized ducks and sham-operated controls (Butler, 1985c). The rate of gain of osmotically free water also doubled in both experimental groups and therefore did not depend on stimulation by adrenocortical steroids (Fig. 4). Oceanic and brackish water birds secrete salt and
conserve osmotically free water with their nasal salt elands because their kidnevs are unable to form a hypertonic urine. Adrenocortical steroids will increase significantly the renalcloaca reabsorption of NaCl during adaptation to fresh water (Holmes and Adams, 1963). They are not, however, required for the functional hypertrophy that follows exposure to saline (Butler, 1980; 1985c) or for the basic level of NaCl secretion by the principal secretory cells of the avian nasal glands (Butler, 1980, 1984, 1985a,b).
gland secretion in Pekin ducks (Anus pluryrhynchos) adapted to 0.9% saline drinking water. Gen. camp. Endocr. (in press).
Diamond J. M. and Tormey J. M. (1966) Role of long extracellular channels in fluid transport across epithelia. Nature, Lond. 210, 817-820. Ellis R. A., Goertemiller C. C. and Stetson D. L. (1977) Significance of extensive leaky cell junctions in avian salt gland. Naiure, Lond. 268, 555-556. Ernst S. A. and Mills J. W. (1977) Basolateral plasma membrane localization of ouabain sensitive sodium transport sites in secretory epithelium of avian salt gland. J. Cell. Biol. 75, 7479.
Ernst S. A. and van Rossum G. D. V. (1982) Ions and energy metabolism in duck salt gland. J. Physiol. 325, 333-352.
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