Atrial natriuretic factor controls salt gland secretion in the Pekin duck (Anas platyrhynchos) through interaction with high affinity receptors.

Marine birds possess supraorbital salt-secreting glands in addition to the kidneys as osmoregulatory organs to excrete a strongly hypertonic salt solution of mainly NaCl. Atrial natriuretic factor (ANF)-like peptides could be demonstrated immunocytochemically in duck atria, but not in the salt glands. To elucidate the putative role of bird-specific ANF (cANF) in the control of salt gland function, conscious saltwater-acclimated Pekin ducks received 15 pmol/min.kg BW cANF for 10 min at two states of salt gland activity. During steady state diuresis and salt gland secretion induced by systemic infusion of 1.0 ml/min isotonic Krebs-Ringer solution, cANF applied iv enhanced the secretion rate from 0.20 to 0.29 ml/min and the osmolality of secretion from 870 to 920 mosmol/kg. At threshold conditions of salt gland activity, cANF infused intracarotideally stimulated the secretion rate from 0.07 to 0.15 ml/min at elevated osmolality of 760 compared to 480 mosmol/kg. Mean arterial pressure and heart rate remained unchanged. Receptor autoradiography with [125I]Bolton-Hunter-cANF as ligand demonstrated specific binding sites throughout the salt gland tissue of both freshwater and saltwater ducks. Scatchard analysis using an enriched membrane fraction revealed high affinity (Kd = 0.9 nM) binding sites of 270 fmol/mg protein density. Displacement studies with unlabeled cANF and human ANF showed comparable Ki values for both peptides in freshwater and saltwater ducks. The combined results indicate an important role for cANF in the control of avian salt gland function.

Demonstration of atrial natriuretic peptide/cardiodilatin (ANP/CDD)-immunoreactivity in the salt gland of the Pekin duck.

A novel peptide hormone, atrial natriuretic factor/cardiodilatin (ANP/CDD), was recently isolated and characterized from mammalian heart. Its presence has been demonstrated in several organs that contribute to water and sodium homeostasis, such as salivary glands. This study demonstrates the presence of ANP/CDD immunoreactivity in the salt gland of Pekin ducks by high performance liquid chromatography, radioimmunoassay and immunocytochemistry, using a specific antibody against atriopeptide I. A small number of distinct, ovoid or cuboid shaped ANP/CDD-immunoreactive cells were localized in the connective tissue surrounding and separating the central secretory tubules, whereas no immunostaining was observed in the peripheral tubules. Salt glands of ducks that were adapted to salt water revealed a significant hypertrophy of their secretory lobules. However, no differences were found between the number or localization of immunoreactive cells in the salt gland of salt water-acclimatized ducks and nonstimulated glands of ducks that were housed with ad libitum access to fresh water. Our results indicate that ANP/CDD may play a role in the regulation of sodium secretion in the salt gland of aquatic birds.

Basolateral plasma membrane localiztion of ouabain-sensitive sodium transport sites in the secretory epithelium of the avian salt gland.

The distribution of Na+ pump sites (Na+-K+-ATPase) in the secretory epithelium of the avian salt gland was demonstrated by freeze-dry autoradiographic analysis of [(3)H] ouabain binding sites. Kinetic studies indicated that near saturation of tissue binding sites occurred when slices of salt glands from salt-stressed ducks were exposed to 2.2 muM ouabain (containing 5 muCi/ml [(3)H]ouabain) for 90 min. Washing with label-free Ringer's solution for 90 min extracted only 10% of the inhibitor, an amount which corresponded to ouabain present in the tissue spaces labeled by [(14)C]insulin. Increasing the KCl concentration of the incubation medium reduced the rate of ouabain binding but not the maximal amount bound. In contrast to the low level of ouabain binding to salt glands of ducks maintained on a freshwater regimen, exposure to a salt water diet led to a more than threefold increase in binding within 9-11 days. This increase paralleled the similar increment in Na+-K+-ATPase activity described previously. [(3)H]ouabain binding sites were localized autoradiographically to the folded basolateral plasma membrane of the principal secretory cells. The luminal surfaces of these cells were unlabeled. Mitotically active peripheral cells were also unlabeled. The cell-specific pattern of [(3)H]ouabain binding to principal secretory cells and the membrane-specific localization of binding sites to the nonluminal surfaces of these cells were identical to the distribution of Na+-K+-ATPase as reflected by the cytochemical localization of ouabain-sensitive and K+-dependent nitrophenyl phosphatase activity. The relationship between the nonluminal localization of Na+-K+-ATPase and the possible role of the enzyme n NaCl secretion is considered in the light of physiological data on electrolyte transport in salt glands and other secretory epithelia.

The control of adaptive hypertrophy in the salt glands of geese and ducks.

1. Factors controlling adaptive hypertrophy, which occurs when marine, or potentially marine, birds drink salt water, have been investigated in geese and ducks using changes in salt-weight weight, RNA and DNA contents as indices of this process. 2. Unilateral post-ganglionic denervation in geese prevented the changes in [RNA] and [RNA]:[DNA] that occurred in the intact gland of birds given salt water for 24 hr; denervation had no significant effect in birds on fresh water throughout. 3. Atropine treatment also prevented the adaptive changes in geese given salt water. 4. In ducks give 0.3 M-NaCl for 48 hr salt-gland weight, [RNA] and [RNA]:[DNA] increase markedly. Treatment of ducks drinking fresh water with large doses of corticosterone and mammalian ACTH for 48 hr had no significant effects on salt-gland weight, RNA or DNA; mammalian prolactin treatment for 48 hr significantly raised [RNA]. 5. No changes in the total amount of DNA in the glands were observed in these experiments, thus indicating that hyperplasia does not occur within 48 hr of a bird first drinking salt water. 6. It is concluded that adaptive hypertrophy is controlled by secretory nerves, and that hormones, if they play any part in this process, have a permissive or secondary role. It is suggested that hypertrophy and the maintenance of the secretory cells in the fully-adapted state may be obligatorily related to secretory activity induced by cholinergic secretory nerves.

Fatty acid and aldehyde composition of major phospholipids in salt gland of marine birds and spiny dogfish.

The lipophilic components of choline phosphoglycerides and ethanolamine phosphoglycerides obtained from the salt gland of herring gull and eider duck and from the rectal gland of spiny dogfish were investigated by means of thin-layer chromatography, gas chromatography, and gas chromatography-mass spectrometry. All phospholipids analyzed were shown to contain small amounts of plasmalogens, and mainly C16, C18, and C18:1 aldehyde was detected. The fatty acids were composed of saturated, unsaturated, straight chain, and branched chain types, ranging between 14-22 carbon atoms. The lipophilic composition of the rectal gland phospholipids showed a higher degree of unsaturation and the presence of more branched chain fatty acids than that of the birds, possibly related to body temperature.

Identification of a xylose-containing cerebroside in the salt gland of the herring gull.

A pentose-containing cerebroside has been identified in the salt gland of the herring gull, using mass spectrometry of acetyl and trimethylsilyl derivatives. A detailed interpretation of the spectra allowed a conclusion concerning the major long-chain base (the C(20) homolog of sphingosine) and the major fatty acids (C(22)-C(25) 2-hydroxy fatty acids), using reference spectra of synthetic galactosylceramides. A six-membered glycose ring (aldopyranose) was demonstrated by mass spectrometry of the acetyl derivative of periodic acid-oxidized and sodium borodeuteride-reduced pentosylceramide. By gas-liquid chromatography and mass spectrometry of methanolysis products, the pentose was shown to be identical with xylose. The procedures were applied to 25-50 micro g of glycolipid.

Intracellular concentrations of sodium, potassium and chloride in the salt-gland of the domestic goose and their relation to the secretory mechanism.

1. The composition of the nasal salt-glands of geese was found to be Na 57 +/- 3.5 (S.E.), K 52.3 +/- 3.9 and Cl 78.3 +/- 11.0 m-equiv/kg fresh tissue. During secretion, the Na content was significantly raised to 72.4 +/- 3.4 m-equiv/kg.2. Salt-gland slices incubated in Krebs-Henseleit bicarbonate medium plus glucose (6 mM), in the presence of [(14)C]sucrose as an extracellular marker had the following composition, Na 85.3 +/- 3.1, K 37.1 +/- 3.1 and Cl 74.3 +/- 3.6 m-equiv/kg. The calculated intracellular concentrations were for Na 61.5 +/- 2.1, K 105.3 +/- 8.7 and Cl 37.8 +/- 5.0 m-equiv/l. intracellular water.3. Ouabain (10(-4)M) significantly decreased the tissue and cell K concentration and significantly increased the Na concentration.4. Acetylcholine (10(-6)M) and eserine (10(-4)M) in the incubation medium had no effect on intracellular composition.5. Raising the Na concentration of the medium to 172 m-equiv/l. and the Cl to 156 m-equiv/l. in two experiments had no effect on the calculated intracellular composition.6. These results do not support reports that the cells have a very high Na concentration (about 350 m-equiv/l. intracellular water). They are compatible with the hypothesis that the hypertonic secretion is formed across the luminal membrane of the secretory cell by an active Na(+) pump and there are no data to suggest that Na(+) is concentrated across the basal membrane by a ouabain-insensitive process.7. The data are discussed in relation to permeability studies and to electrical potential measurements within the gland by other workers.