Attraction and Electrophysiological Response to Identified Rectal Gland Volatiles in Bactrocera frauenfeldi (Schiner).

Bactrocera frauenfeldi (Schiner) (Diptera: Tephritidae) is a polyphagous fruit fly pest species that is endemic to Papua New Guinea and has become established in several Pacific Islands and Australia. Despite its economic importance for many crops and the key role of chemical-mediated sexual communication in the reproductive biology of tephritid fruit flies, as well as the potential application of pheromones as attractants, there have been no studies investigating the identity or activity of rectal gland secretions or emission profiles of this species. The present study (1) identifies the chemical profile of volatile compounds produced in rectal glands and released by B. frauenfeldi, (2) investigates which of the volatile compounds elicit an electroantennographic or electropalpographic response, and (3) investigates the potential function of glandular emissions as mate-attracting sex pheromones. Rectal gland extracts and headspace collections from sexually mature males and females of B. frauenfeldi were analysed by gas chromatography-mass spectrometry. Male rectal glands contained (E,E)-2-ethyl-8-methyl-1,7-dioxaspiro [5.5]undecane as a major component and (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane as a moderate component. Minor components included palmitoleic acid, palmitic acid, and ethyl oleate. In contrast, female rectal glands contained (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane and ethyl laurate as major components, ethyl myristate and ethyl palmitoleate as moderate components, and 18 minor compounds including amides, esters, and spiroacetals. Although fewer compounds were detected from the headspace collections of both males and females than from the gland extractions, most of the abundant chemicals in the rectal gland extracts were also detected in the headspace collections. Gas chromatography coupled electroantennographic detection found responses to (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane from the antennae of both male and female B. frauenfeldi. Responses to (E,E)-2-ethyl-8-methyl-1,7-dioxaspiro[5.5]undecane were elicited from the antennae of females but not males. The two spiroacetals also elicited electropalpographic responses from both male and female B. frauenfeldi. Ethyl caprate and methyl laurate, found in female rectal glands, elicited responses in female antennae and palps, respectively. Y-maze bioassays showed that females were attracted to the volatiles from male rectal glands but males were not. Neither males nor females were attracted to the volatiles from female rectal glands. Our findings suggest (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane and (E,E)-2-ethyl-8-methyl-1,7-dioxaspiro[5.5]undecane as components of a sex-attracting pheromone in B. frauenfeldi.

THE SHARK RECTAL GLAND MODEL: A CHAMPION OF RECEPTOR MEDIATED CHLORIDE SECRETION THROUGH CFTR.

The dogfish shark salt gland was predicted by Smith and discovered by Burger at the Mount Desert Island Biological Laboratory in Salisbury Cove, Maine. It is an epithelial organ in the intestine composed of tubules that serve a single function: the secretion of hypertonic NaCl. Many G protein receptors are present on the basolateral surface of these tubules, including stimulatory receptors for vasoactive intestinal peptide, adenosine A2, growth hormone releasing hormone, and inhibitory receptors for somatostatin and adenosine A1. An entirely different class of stimulatory receptors is present as C-type natriuretic peptide receptors. Each stimulatory receptor evokes powerful NaCl secretion. G protein receptors bind to Gαs to activate the catalytic unit of adenylate cyclase to form cyclic adenosine monophosphate (cAMP) and protein kinase A that phosphorylates the regulatory domain of cystic fibrosis transmembrane conductance regulator, opening the channel. The C-type natriuretic peptide receptor stimulates by activating guanylate cyclase and endogenous cyclic guanosine monophosphate which inhibits type 3 phosphodiesterase, the enzyme that breaks down cAMP, thereby elevating cAMP and activating the protein kinase A pathway.

Effects of short-term hyper- and hypo-osmotic exposure on the osmoregulatory strategy of unfed North Pacific spiny dogfish (Squalus suckleyi).

The North Pacific spiny dogfish (Squalus suckleyi) is a partially euryhaline species of elasmobranch that often enter estuaries where they experience relatively large fluctuations in environmental salinity that can affect plasma osmolality. Previous studies have investigated the effects of altered salinity on elasmobranchs over the long term, but fewer studies have conducted time courses to investigate how rapidly they can adapt to such changes. In this study, we exposed unfed (no exogenous source of nitrogen or TMAO) spiny dogfish to hyper- and hypo-osmotic conditions and measured plasma and tissue osmolytes, nitrogen excretion, and changes in enzyme activity and mRNA levels in the rectal gland over 24h. It was shown that plasma osmolality changes to approximately match the ambient seawater within 18-24h. In the hypersaline environment, significant increases in urea, sodium, and chloride were observed, whereas in the hyposaline environment, only significant decreases in TMAO and sodium were observed. Both urea and ammonia excretion increased at low salinities suggesting a reduction in urea retention and possibly urea production. qPCR and enzyme activity data for Na(+)/K(+)-ATPase did not support the idea of rectal gland activation following exposure to increased salinities. Therefore, we suggest that the rectal gland may not be a quantitatively important aspect of the dogfish osmoregulatory strategy during changes in environmental salinity, or it may be active only in the very early stages (i.e., less than 6h) of responses to altered salinity.

Osmoregulatory and metabolic costs of salt excretion in the Rufous-collared sparrow Zonotrichia capensis.

Recent experiments on shorebirds have demonstrated that maintaining an active osmoregulatory machinery is energetically expensive. This may, in part, explain diet and habitat selection in birds with salt glands. However little is known about the osmoregulatory costs in birds lacking functional salt glands. In these birds, osmotic work is done almost exclusively by the kidneys. We investigated the osmoregulatory cost in a bird species lacking functional salt glands, the passerine Zonotrichia capensis. After 20 days of acclimation to fresh water (FW) and salt water (200 mM NaCl, SW), SW birds tended to be heavier than FW birds. However, this difference was not statistically significant. Total basal metabolic rate was higher in SW birds as compared with FW birds. Renal and heart masses were also higher in the SW group. We also found greater medullary development and an increase in urine osmolality in the SW group. In spite of Z. capensis' ability to tolerate a moderate salt load in the laboratory, we hypothesize that increased cost of maintenance produced by salt consumption may significantly affect energy budget, dietary, and habitat choices in the field.

Are the glandular trichomes in Jacquinia armillaris (Theophrastoideae-Primulaceae) salt glands?

Salt stress is harmful to plants, especially for those that live under conditions of intense salt aport. For this reason, several species present alternatives to prevent or diminish the damages that high salt concentrations may cause to the cells. Salt glands are one of these alternatives once they are specialized structures that secrete salt. Here, we aimed to investigate if the glandular trichomes in the leaves of Jacquinia armillaris are salt glands. Anatomical and ultrastructural observations showed that the glandular trichomes in J. armillaris resemble the salt glands from other recretohalophytes Primulaceae, such as, their occurrence in sunken regions in the leaf epidermis, the presence of a large basal cell that acts as a collecting cell, the detachment of the cuticle from the outer periclinal walls forming a cuticular chamber, the thickness of the cuticle in the stalk portion of the trichome, and the presence of sodium and chloride ions in the secretion and in the xylem. Altogether, the gathered results support the hypothesis that the glandular trichomes in J. armillaris are adapted to salt secretion, thus characterizing as salt glands.

Characterization of muscarinic acetylcholine receptors in the avian salt gland.

Electrolyte and fluid secretion by the avian salt gland is regulated by activation of muscarinic acetylcholine receptors (R). In this study, these receptors were characterized and quantitated in homogenates of salt gland from domestic ducks adapted to conditions of low (freshwater, FW) and high (saltwater, SW) salt stress using the cholinergic antagonist [3H]-quinuclidinyl benzilate (QNB). Specific binding of the antagonist to receptors in both FW- and SW-adapted glands reveals a single population of high affinity binding sites (KdFW = 40.1 +/- 3.0 pM; KdSW = 35.1 +/- 2.1 pM). Binding is saturable; RLmaxFW = 1.73 +/- 0.10 fmol/micrograms DNA; RLmaxSW = 4.16 +/- 0.31 fmol/micrograms DNA (where L is [3H]QNB and RL the high affinity complex). Calculated average cellular receptor populations of 5,800 sites/cell in FW-adapted glands and 14,100 sites/cell in SW-adapted glands demonstrate that upward regulation of acetylcholine receptors in the secretory epithelium follows chronic salt stress. The receptor exhibits typical pharmacological specificities for muscarinic cholinergic antagonists (QNB, atropine, scopolamine) and agonists (oxotremorine, methacholine, carbachol). In addition, the loop diuretic furosemide, which interferes with ion transport processes in the salt gland, competitively inhibits [3H]QNB binding. Preliminary studies of furosemide effects on [3H]QNB binding to rat exorbital lacrimal gland membranes showed a similar inhibition, although the diuretic had no effect on antagonist binding to rat brain or atrial receptors.

An endogenous peptide stimulates secretory activity in the elasmobranch rectal gland.

Extraction and partial purification of peptide material from the intestine of the elasmobranch Scyliorhinus canicula yielded a fraction that shows potent stimulatory activity in the rectal gland. The extracted material appears to contain an endogenous peptide (or peptides) that represents the natural hormone responsible for the control of rectal gland secretion in vivo.

Adaptive strategies for post-renal handling of urine in birds.

Birds are a diverse vertebrate class in terms of diet and habitat, but they share several common physiological features, including the use of uric acid as the major nitrogenous waste product and the lack of a urinary bladder. Instead, ureteral urine refluxes from the urodeum into the more proximal coprodeum and portions of the hindgut (colon or rectum and ceca). This presents a potential problem in that hyperosmotic ureteral urine in contact with the permeable epithelia of these tissues would counteract renal osmotic work. This review describes and provides examples of different strategies used by avian species to balance renal and post-renal changes in urine composition. The strategies described include: 1. a "reptilian" mode, with moderate renal concentrating ability, but high rates of post-renal salt and water resorption; 2. the "mammalian" strategy, in which the coprodeum effectively functions like a mammalian urinary bladder, preserving the osmotic concentrating work of the kidney; 3. an interaction strategy, in which post-renal transport processes are hormonally regulated in order to optimize renal function under varying conditions of salt or water stress; 4. the salt gland strategy seen in marine or estuarine birds with functional salt glands, in which post-renal transport mechanisms are used to conserve urinary water and to recycle excess NaCl to the nasal salt glands. Finally, we also describe some features of an as-yet unstudied group of birds, the birds of prey. At least some species in this group are relatively good renal concentrators, and would be predicted to have post-renal mechanisms to preserve this work. This new synthesis illustrates the marked diversity of adaptive mechanisms used by avian species to maintain osmotic homeostasis.

Control of rectal gland secretion by blood acid-base status in the intact dogfish shark (Squalus acanthias).

In order to address the possible role of blood acid-base status in controlling the rectal gland, dogfish were fitted with indwelling arterial catheters for blood sampling and rectal gland catheters for secretion collection. In intact, unanaesthetized animals, isosmotic volume loading with 500 mmol L-1 NaCl at a rate of 15 mL kg-1 h-1 produced a brisk, stable rectal gland secretion flow of about 4 mL kg-1 h-1. Secretion composition (500 mmol L-1 Na+ and Cl-; 5 mmol L-1 K+; <1 mmol L-1 Ca2+, Mg2+, SO(4)2-, or phosphate) was almost identical to that of the infusate with a pH of about 7.2, HCO3- mmol L-1<1 mmol L-1 and a PCO2 (1 Torr) close to PaCO2. Experimental treatments superimposed on the infusion caused the expected disturbances in systemic acid-base status: respiratory acidosis by exposure to high environmental PCO2, metabolic acidosis by infusion of HCl, and metabolic alkalosis by infusion of NaHCO3. Secretion flow decreased markedly with acidosis and increased with alkalosis, in a linear relationship with extracellular pH. Secretion composition did not change, apart from alterations in its acid-base status, and made negligible contribution to overall acid-base balance. An adaptive control of rectal gland secretion by systemic acid-base status is postulated-stimulation by the "alkaline tide" accompanying the volume load of feeding and inhibition by the metabolic acidosis accompanying the volume contraction of exercise.

K+-induced swelling of the dogfish shark (Squalus acanthias) rectal gland cells is associated with changes of the cytoskeleton.

Dogfish shark (Squalus acanthias) rectal gland cells swell massively when incubated in elasmobranch media in which Na+ was equivalently replaced by K+; this swelling was abolished when the impermeant gluconate replaced Cl-, while the cell depolarization was comparable in both media. The K+-effect was associated with (a) an increase of the steady-state 42K (and 86Rb) efflux (particularly of the rate constant of the fast cellular efflux component) and a rearrangement of the respective cellular pools of K+; (b) an alteration of cell morphology and the pattern of the F-actin staining along the basolateral cell membrane as revealed with fluorescent analogs of phallacidin. These changes were independent of cell volume, being identical in KCl and K-gluconate media. The observations were specific for K+ (and Rb+): replacement of media Na+ by Li+ (which is not actively extruded by the cells), or the presence of ouabain, produced only minor swelling without affecting cell morphology and F-acting distribution. The results are consistent with the following view: as opposed to Na+ or Li+ media, the K+-induced changes of the cortical F-actin component of the cytoskeleton permit the observed massive cell swelling due to the osmotic contribution of intracellular impermeant anion(s).

Two K+ channel types, muscarinic agonist-activated and inwardly rectifying, in a Cl- secretory epithelium: the avian salt gland.

Patches of membrane on cells isolated from the nasal salt gland of the domestic duck typically contained two types of K+ channel. One was a large-conductance ("maxi") K+ channel which was activated by intracellular calcium and/or depolarizing membrane voltages, and the other was a smaller-conductance K+ channel which exhibited at least two conductance levels and displayed pronounced inward rectification. Barium blocked both channels, but tetraethylammonium chloride and quinidine selectively blocked the larger K+ channel. The large K+ channel did not appear to open under resting conditions but could be activated by application of the muscarinic agonist, carbachol. The smaller channels were open under resting conditions but the gating was not affected by carbachol. Both of these channels reside in the basolateral membranes of the Cl- secretory cells but they appear to play different roles in the life of the cell.

Cloning of sgk serine-threonine protein kinase from shark rectal gland ­ a gene induced by hypertonicity and secretagogues.

Recently, the cell-volume-regulated serine-threonine protein kinase h-sgk was cloned from a human hepatoma cell line. The sgk gene was shown to be induced by cell shrinkage in many different mammalian cell lines. In this study, two highly conserved serine-threonine protein kinases, sgk-1 and sgk-2, were cloned from rectal gland tissue of the spiny dogfish (Squalus acanthias). Both kinases showed a distinct pattern of tissue specificity, with high expression levels in kidney, intestine, liver and heart. In rectal gland slices sgk-1 transcription was induced by exposure to hypertonic solution, reduction of the extracellular urea concentration, and addition of the secretagogues vasoactive intestinal polypeptide (VIP) and carbachol. The shark sgk-1 serine-threonine protein kinase may therefore provide a link between cell volume, Cl­secretion and protein phosphorylation state in shark rectal gland cells.

Na-K-Cl cotransport in chloride-transporting epithelia.

The elasmobranch rectal gland has served as a useful model to study features of Na-K-Cl cotransport that are common to many chloride-transporting epithelia. These include: (1) dependence on a Na+ gradient created by Na-K-ATPase; (2) high intracellular Cl- concentration; (3) characteristic inhibitor profile including inhibition by loop diuretics and barium but not by amiloride, SITS, DIDS, or carbonic anhydrase inhibitors; and (4) remarkable energy efficiency of transepithelial transport (25-30 NaCl/l 02). The mechanism by which this is accomplished is clarified by kinetic analysis of experiments with isolated perfused rectal glands of Squalus acanthias in which perfusate concentrations of Na and Cl are systematically varied. These show a Hill coefficient of one for Na+ and two for Cl-, suggesting that one Na+, one K+, and two Cl- interact with the cotransport carrier. Nitrate can substitute for Cl- to some extent, and it itself weakly transported. The loop diuretic bumetanide behaves like a competitive inhibitor of Cl-. The teleological significance of the neutral cotransport of two Cl- with one Na+ and one K+ is that it enables transporting epithelia like the rectal gland, cornea, salivary gland, and thick ascending limb of Henle's loop to double the efficiency of their Na-K-ATPase pump.

Central action of nitric oxide in the saltwater-acclimated duck: modulation of extrarenal sodium excretion and vasotocin release.

Hypothalamic nuclei close to the third ventricle (VIII) represent key structures in avian osmoregulation concerned with the control of salt gland activity and release of the antidiuretic hormone [Arg8]vasotocin (AVT). Nitric oxide (NO) acting as a paracrine transmitter in the hypothalamus has been shown to contribute to the maintenance of salt and fluid balance in mammals. The saltwater-acclimated duck was used in the present study as a well-characterized osmoregulatory model to investigate the role of central NO in hypothalamic perception or integration of osmoregulatory signals in marine birds. During osmotically induced steady-state salt gland secretion, the VIII of conscious ducks was microperfused with artificial cerebrospinal fluid (aCSF) alone, aCSF containing the NO-donor SNAP or the peptide [Val5]angiotensin II (ANGII) and alterations in salt gland activity, arterial pressure and the release of AVT were continuously monitored. No changes occurred during intracerebroventricular microperfusion with aCSF. Central application of ANGII, a known inhibitory hypothalamic transmitter in the control of salt gland function, markedly blocked salt gland osmolal excretion. Central stimulation with the NO-donor SNAP significantly reduced osmolal excretion from 0.41+/-0.02 to 0. 22+/-0.04 mosmol/min. Both ANGII and SNAP caused a rise in plasma AVT at either slightly elevated (ANGII) or constant (SNAP) arterial pressure. Employing NADPH-diaphorase histochemistry in the duck hypothalamus to localize sites of NO synthesis, periventricular neurons, nerve fibers in close association to the VIII and also parvocellular neurons of the paraventricular nucleus could be labeled. These data suggest a modulatory role for hypothalamic NO within the central osmoregulatory circuitry controlling salt gland function and AVT release in marine birds.

Inhibition of chloride secretion by BaCl2 in the rectal gland of the spiny dogfish, Squalus acanthias.

In the rectal gland of the spiny dogfish (Squalus acanthias), chloride enters the cell via a cotransport system together with sodium and potassium in a 2 Cl-: 1 Na+: 1 K+ stoichiometry. The system is energized by the electrochemical potential for sodium directed into the cell. Sodium is extruded from the cell by Na-K-ATPase located on the basolateral cell membrane. Chloride leaks into the lumen following a favorable electrical gradient. Potassium is thought to recirculate across the basolateral cell membrane. Since barium ions inhibit the efflux of potassium from cells we used barium chloride to explore the role of potassium in the process of stimulated secretion of chloride by the gland. The secretion of chloride was stimulated with theophylline 2.5 X 10(-4)M and dibutyryl cyclic AMP 5 X 10(-5)M. Ba++ inhibited the secretion of chloride in a way that was reversible and dose dependent. The reduction in secretion was associated with a parallel fall in transglandular electrical potential. Inhibition was half maximal at a concentration of Ba++ of 10(-3)M. The reduction in efflux of potassium produced by Ba++ presumably decreases the potassium diffusion potential, thus reducing the electronegativity of the cell and dissipating the driving force for chloride across the apical cell membrane. Recirculation of K+ across the basolateral border of the cell would thus be essential for the maintenance of chloride secretion by the gland.

Electrophysiological properties of different cell types in the shark rectal gland.

Electrophysiological properties of different cell types were studied in single rectal gland cells of Squalus acanthias by the whole-cell voltage clamp technique. Based on electrophysiological characteristics and primary morphological observations (light microscope, X400), three cell types (named as I, II, and III) were found in isolated fresh cells and two cell types (I and II) in primary cultured cells of the shark rectal gland (SRG). Type I cells had both Cl- (I(Cl)) and the inwardly rectifying K+ channel (I(K1)). Type II and III cells only had I(Cl) Under X400 light microscope granular materials in the cytoplasm were found in Type I and II cells, but not in Type III cells. The data from this study show that 65 % of isolated fresh SRG cells strongly expressed the K+ channel with much less amount of the Cl- channel and 35% had only I(Cl). In sharp contrast, 11% had I(K1) and I(Cl), and 89% had only I(Cl) in cultured SRG cells. Extracellular application of 10 microM forskolin significantly enhanced I(Cl) in primary cultured SRG cells. This enhancement was influenced by intracellular Ca2+ and blocked by 50 microM Ni2+. Other compounds, such as vasoactive intestinal peptide (VIP) and 8-(4-chlorophenylthio)-adenosine3':5'-cyclic monophosphate (cpt-cAMP) also enhanced I(Cl). Interestingly, cAMP and forskolin significantly inhibited I(K1) in cultured and fresh SRG cells. I(K1) was blocked by micromolar concentrations of Ba2+ and significantly altered by extracellular K+ concentrations. The present data suggest that 1) the shark rectal gland contains different cell types which may play various roles in the process of salt secretion; 2) I(Cl) and I(K1) in SRG cells are strongly modulated by cAMP, forskolin, and VIP, as well as Ca2+, K+, and Na+ ions.

Effects of cadmium ingestion on plasma and osmoregulatory hormone concentrations in male and female Pekin ducks.

Effects of ingested cadmium (Cd) on body mass and plasma, urine, salt-gland secretion, and osmoregulatory hormone concentrations were assessed in male and female Pekin ducks, Anas platyrhynchos, acclimated to 450 mM NaCl over 6 wk and then held an additional 13 wk on 300 mM NaCl (prolonged saline exposure). Groups of six birds ate diets containing 0 (control), 50 (low-Cd diet), or 300 (high Cd diet) micrograms Cd/g food. Ducks that ingested Cd, especially females, lost body mass. Cadmium ingestion did not affect salt-gland secretion concentration. Control males had higher plasma osmolality and lower relative plasma volume. These increased in both sexes during saline acclimation. The high-Cd diet suppressed the increase in plasma osmolality in both sexes, but a rise in relative plasma volume occurred only in females. Following prolonged exposure to saline, plasma osmolality and relative plasma volume were reduced in control ducks but further elevated in ducks on the high-Cd diet. Cadmium ingestion suppressed the increase in urine osmolality that occurred in control ducks during saline acclimation. Neither saline acclimation nor Cd ingestion affected plasma concentrations of arginine vasotocin or prolactin. Arginine vasotocin was not correlated with plasma osmolality; prolactin was negatively correlated with plasma osmolality, but only in males. Cadmium suppressed the increase in angiotensin II that occurred at higher salinities in control and low-Cd males. This study examined the effects of gradually increasing body cadmium content on osmotic homeostasis. Cadmium affected plasma and urine, but not salt-gland secretion, concentrations and some of these responses were sexually disparate. Cadmium did not affect osmoregulatory hormones (arginine vasotocin and prolactin) by which observed changes in plasma concentration might have been influenced.

Ion secretion by salt glands of desert iguanas (Dipsosaurus dorsalis).

Unlike the NaCl-secreting salt glands of many birds and reptiles, the nasal salt glands of lizards can secrete potassium as well as sodium, with either chloride or bicarbonate as the accompanying anion. The factors responsible for initiating secretion by the gland and the rates of cation and anion secretion were studied in the desert iguana, Dipsosaurus dorsalis. Lizards were given combinations of ions for several days, and secreted salt was collected daily and analyzed for sodium, potassium, chloride, and bicarbonate. Maximum total cation secretion rate was 4.4+/-0.38 micromol/g/d. Cation secretion ranged from 24% to 100% potassium; even high NaCl loads did not abolish potassium secretion. Maximum bicarbonate secretion was about 0.5 micromol/g/d; chloride was the predominant anion. Secretion rate increased only in response to those treatments that included potassium and/or chloride; sodium ions and other osmotic loads (e.g., sucrose) did not increase secretion. This is in contrast to birds and some other reptiles with salt glands, which initiate NaCl secretion in response to any osmotic load. The specificity of the response of the salt gland of Dipsosaurus may be related to the ecological importance of dietary potassium and chloride for herbivorous desert lizards.

Renal function in freshwater and chronically saline-stressed male and female Pekin ducks.

Hematocrit (Hct) and plasma ionic and osmotic concentrations were measured in Pekin Ducks, Anas platyrhynchos, drinking freshwater (FW), during rapid acclimation to sea water (RA), and after 6 mo exposure to 180-mM NaCl (SW). Glomerular filtration rate (GFR) and extracellular fluid volume (ECFV) were measured in FW and SW ducks. Estimated renal plasma flow (ERPF) was measured in SW ducks. During RA, Hct and plasma concentration increased significantly (P less than .05) when drinking water sodium concentration ([Na]dw) was 300 mM; body mass decreased (P less than .01) when [Na]dw was 375 mM. The Hct and plasma ionic or osmotic concentrations of FW and SW ducks were the same, except that female SW ducks had lower (P less than .05) plasma chloride concentrations than FW female ducks. Relative to body mass, the FW female duck ECFV (26.88%) was larger (P less than .01) than that of the male (17.50%). The ECFV was not affected by SW in either sex. Mean (+/- SE) GFR determined using inulin and polyethylene glycol (PEG) in the same five FW ducks, were the same, 4.4 +/- .7 and 4.7 +/- .6 mL(min.kg)-1, respectively. In female FW ducks, the GFR (PEG) was 5.00 +/- .30 mL(min.kg)-1, significantly (P less than .001) greater than that of the male, which was 3.07 +/- .21 mL(min.kg)-1. Female and male SW duck GFR were 3.96 +/- .57 and 2.60 +/- .37 mL(min.kg)-1, respectively, but the decrease in GFR was significant (P less than .05) only for females. The GFR were the same, relative to kidney mass, in both sexes.(ABSTRACT TRUNCATED AT 250 WORDS)

[The physiological determinants of the parallelism (unity) of histological structures]. / Fiziologicheskie determinanty parallelizma (edinstva) gistologicheskikh struktur.

The theory of structural parallelism put forward by A. A. Zavarzin (Senior) has been supported by the analysis of cytological specificity of effector organs involved in water-salt homeostasis, and of the excretory system of vertebrates and invertebrates. The similarity in morphofunctional organization of different excretory organs (i.e. the presence of ultrafiltration apparatus and cells which make it possible to absorb all vitally important substances) is likely to result from the fact that the excretory organ should excrete not only the final products of metabolism, but also any exogenic substances in addition to those which although important, are excessive for the organism. The brush border of asymmetrical epithelial cells of excretory organs is presumably a morphological expression of the structure which accounts for the inward transport of all physiologically important substances. Specificity of the membrane mechanism of water and sodium transport accounts for the identical principles in the structure of cells and areas of cell contacts of epithelia in different organs involved in the formation of hypotonic (saliva glands, renal tubules) or hypertonic fluids (salt glands, marine teleost gills).