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The duct system of the lachrymal salt gland of the green sea turtle comprises central canals, secondary ducts and a sac-like main duct. Distally the central canals consist of large columnar cells with lateral membranes folded into plicae which interdigitate in adjacent cells to form complex intercellular spaces. More proximally the central canals, secondary ducts and main duct consist of epithelia which are stratified or pseudostratified. The cells of these epithelia are separated by wide and complex inter-cellular spaces: they are joined by frequent maculae adherentes junctions. Complex intracellular webs of tonofilaments are associated with these junctions. At the luminal border of the epithelia of the secondary and main ducts is a layer of mucocytes. The mucocytes increase in density towards the proximal extremity of the main duct and secrete a thick luminal layer of mucus. The duct system is very well vascularised. It is suggested that it is unlikely to be merely a passive conduit and that it may have a role in the modification of the fluid secreted by the gland.

The functional zonation in the adrenocortical tissue of the duck was experimentally investigated after chronic administration of corticosteroids of different types (corticosterone, desoxycorticosterone, dexamethasone) and salt loading (chlorides of sodium and potassium). The cytomorphology of the interrenal cells belonging to subcapsular and central zones was explored by light- and electron microscopy and by biochemical analysis of plasma corticosterone. Corticoid-induced involution of the interrenal tissue, or hyperactivity elicited by salt loading were evident in both subcapsular and central regions of the gland. In the duck the adrenocortical tissue appears to be devoid of steroidogenic functional differentiation. The modifications of different cellular organelles and inclusions can be explained in the light of known concepts about corticosteroid metabolism. The depression of plasma corticosterone titre in corticosteroid-treated animals agrees with the image of cytological inhibition. The lowered corticosterone value in KCl-loaded ducks signifies increased peripheral metabolism of this hormone. The hypercorticosteronemia in NaCl-loaded ducks is probably related to activation of the nasal gland under osmotic stress.

This study provides information on the rates of DNA synthesis, sites of DNA synthesis, and DNA content of the avian salt gland during the osmotic stressing (plasma membrane synthesis) and destressing (plasma membrane turnover) cycle, in an effort to better understand the relationship of cell turnover to the initial events in plasma membrane amplification, differentiation, and turnover. The rate of DNA synthesis increases 12--24 h after the onset of osmotic stress, is maximal at about 24 h of osmotic stress, and decreases thereafter in fully stressed and destressed glands. The maximum DNA and protein content, and the maximum protein/DNA ratio are obtained after about 3 days of stress. Autoradiograms show that at 24 hr of stress 70--80% of DNA synthesis occurs in connective tissue cells and 20--30% in parenchymal cells, but by 6 days of stress, synthesis occurs about equally in these cell groups. Because destressing is characterized by a large decrease in plasma membrane and in glandular protein, but by little DNA turnover or loss, the loss of plasma membrane is likely due to some type of cell dedifferentiation rather than cell turnover.

In saltwater-acclimated ducks with fully specialized supraorbital salt glands, intracarotid application of acetylcholine (5 nmoles/min/kg b.w.) or porcine vasoactive intestinal polypeptide (pVIP) (240 pmoles/min/kg b.w.) induced secretion from the salt glands at threshold conditions of secretory activity. pVIP-like immunoreactivity could be localized in fibers of the postganglionic secretory nerve ramifying throughout the glandular parenchyma. Both middle-sized arterioles and secretory tubules were innervated, and pVIP-immunoreactive varicose fibers formed peritubular baskets around the basal region of secretory tubules indicating direct innervation of the secretory tissue. pVIP-specific staining could be abolished by preabsorption of the antiserum with peptide extracts of salt-gland tissue. Synthetic pVIP and endogenous VIP from salt glands of the duck co-eluted on the HPLC system, suggesting structural similarity of the peptides. Membrane-binding studies with radioiodinated pVIP revealed the presence of high-affinity binding sites in salt-gland tissue. Affinities of unlabeled pVIP analogues to compete for these binding sites were as follows: pVIP greater than PHI greater than pVIP antagonist greater than secretion greater than pVIP (10-28) greater than chicken VIP (16-28). Peptide extracts of salt glands had affinities similar to pVIP. Binding sites could be localized mainly at the apical end of the radially arranged secretory tubules, as demonstrated by receptor autoradiography. It is concluded that, in addition to the classical parasympathetic transmitter acetylcholine, VIP serves as neuromodulator/transmitter in cranial parasympathetic control of avian salt-gland secretion by acting on both the arteriolar network and the secretory tubules of the gland.

The anatomy, histology, ultrastructure and ATPase activity of the intramural rectal gland of the chondrichthyean Hydrolagus colliei, are described. The cells of the rectal gland of Hydrolagus demonstrate the same well developed lateral and basal cisternae, elongate mitochondria and luminal border as those of their elasmobranch counterparts. ATPase activity within the rectal gland of Hydrolagus is as intense as that in a number of elasmobranchs examined in the course of the study. Despite its primitive intramural location the rectal gland of Hydrolagus respresents a homolog of the more specialized and better known elasmobranch gland and appears as well suited for cation excretion.

The duct system of the nasal salt gland of the duck comprises central central canals, secondary ducts and main ducts. The secondary and main ducts consist of a layer of columnar cells overlying a layer of small cuboidal cells. The columnar cells have complex intercellular spaces showing evidence of Na+K+-ATPase at the apical regions. Approximately 70% of surface area of the duct system is external to the gland. During adaptation to salt water the duct system increases in size as does the gland. Although the components of the gland of adapted ducks, including the duct system within the gland, increase in size compared with normal ducks, the percentage volume densities of the components remain similar in both categories of ducks, i.e. the duct system increases in size in proportion to the glandular tissue. The volume of the duct system external to the gland is six to seven times larger than the volume within the gland. Thus, if ductal modification of secreted fluid occurs, it will be most likely to take place in the ducts external to the gland. Total surface areas of the duct system were measured from serial sections of glands and ducts from one normal and one adapted duck. These were used to calculate possible flux rates of water and sodium across the duct epithelium, assuming the occurrence of either water reabsorption of sodium secretion. Although these flux rates are high it is shown that they are similar to calculated flux rates across the luminal surface of the secretory tubules.

Both ruthenium red and dialyzed iron techniques indicated that anionic protein-carbohydrates were associated with the plasmalemma of secretory cells in mallard salt glands. Digestion of the tissue with neuraminidase prior to dialyzed iron staining provided evidence that much of the anionic nature of this surface was due to sialic acid. These results were confirmed by biochemical assays showing that the salt-gland tissue contained a relatively high sialic-acid content and that the amount of sialic acid increased with salt-water adaptation. Possible roles of these anionic sites are discussed in relation to currently accepted hypotheses of electrolyte transport.

The mechanism of plasma membrane turnover was investigated using the duckling salt gland as a model system. Feeding fresh water to salt-stressed ducklings results in a decrease in the Na, K-ATPase in salt gland to non-stressed levels in about 7 days, as measured by ATP hydrolysis and 3H-ouabain binding. Electron micrographs reveal that this is accompanied by a decrease in plasma membrane infoldings on the basal and lateral borders of gland secretory cells. Simultaneously there is an increase in filamentous material and a rise in acid phosphatase and peptidase activities in these cells. Cytochemistry shows that the acid phosphatase activity is mostly associated with the basal or basolateral regions of secretory cells. These ovservations could indicate that the removal of plasma membrane components is accomplished by internalization and digestion within the secretory cells.

Using two independent techniques, histochemistry and autoradiography, an enzyme (E.C. 3.6.1.3.) has been localized on basolateral cell membranes of salt secreting cells in the lachrymal gland of Malaclemys. This enzyme is ouabain sensitive. In addition an L-tetramisole sensitive alkaline phosphatase is found in the same sites, and an ethacrynic acid sensitive K+-stimulated p-NPPase is found on the apical membrane. The significance of these results with regard to the location of the pump responsible for net transepithelial sodium transport is discussed.

Tissue from the digitiform rectal gland of the spiny dogfish, Squalus acanthias, was fixed briefly by formaldehyde perfusion and studied for the specificity and localization of p-nitrophenyl phosphatase (NPP'ase) activity. The enzymatic activity was K+-dependent (56%) and ouabain-sensitive (67% inhibition). The electron-dense reaction product (SrPO4) of the cytochemical reaction (Ernst, 1972b) was localized along the inner surfaces of the basolateral membranes of the secretory cells. It was absent from mitochondria, nuclei, vesicles, and other organelles. The luminal surface of the secretory cells was slightly reactive. On the basis of (1) this pattern of localization for the sodium transport system, (2) the presence of extensive intercellular labyrinthine channels (Bulger, 1963) that would facilitate “standing gradients” (Diamond and Bossert, 1968), and (3) the specific distribution of the energy-providing mitochondria, we conclude that the concentration and electrochemical gradients recorded from the secreting gland (Hayslett et al., 1974) are maintained across the domains of the basolateral surfaces of the secretory cells.