Comparative histochemical observations on the excretory system of helminth parasites.

The excretory canals of Ascaridia galli (Nematoda) and the protonephridial ducts of Cotylophoron cotylophorum (Trematoda) and Raillietina cesticillus (Cestoda) have been studied with regard to the histochemical localization of lipids, carbohydrates and hydrolytic enzymes. Distinct excretory organs are absent in the acanthocephalan Centrorhynchus corvi. Triglycerides, phospholipids and lipoproteins are seen in association with the wall of excretory canals of A. galli and R. cesticillus, and phospholipids and lipoproteins at the corresponding site in C. cotylophorum. The physiological significance of lipids in association with excretion of substances has been discussed. Low molecular weight glycogen is present in the lumen of excretory canal of A. galli but not in other worms. The common feature of the excretory canals is the presence of enzyme activities of nonspecific alkaline phosphatase and Mg2+-dependent ATPase. Activity of acid phosphatase is seen only in the excretory canals of A. galli. Glucose-6-phosphatase is present in A. galli and C. cotylophorum and absent in R. cesticillus. Weak reaction of 5'-nucleotidase is present in the excretory canals of helminth species studied here. The role of these enzymes in transportation of substances across the wall of excretory canals and also in ionic regulation has been discussed in detail.     

The role of GDNF in patterning the excretory system

Mesenchymal-epithelial interactions are an important source of information for pattern formation during organogenesis. In the developing excretory system, one of the secreted mesenchymal factors thought to play a critical role in patterning the growth and branching of the epithelial ureteric bud is GDNF. We have tested the requirement for GDNF as a paracrine chemoattractive factor by altering its site of expression during excretory system development. Normally, GDNF is secreted by the metanephric mesenchyme and acts via receptors on the Wolffian duct and ureteric bud epithelium. Misexpression of GDNF in the Wolffian duct and ureteric buds resulted in formation of multiple, ectopic buds, which branched independently of the metanephric mesenchyme. This confirmed the ability of GDNF to induce ureter outgrowth and epithelial branching in vivo. However, in mutant mice lacking endogenous GDNF, kidney development was rescued to a substantial degree by GDNF supplied only by the Wolffian duct and ureteric bud. These results indicate that mesenchymal GDNF is not required as a chemoattractive factor to pattern the growth of the ureteric bud within the developing kidney, and that any positional information provided by the mesenchymal expression of GDNF may provide for renal branching morphogenesis is redundant with other signals.     

A mucosal IgA-mediated excretory immune system in vivo

The capacity of mucosal IgA Abs to serve as an excretory immune system in vivo was investigated. Mice expressing a transgenic TCR were immunized intragastrically with the cognate Ag to elicit a vigorous mucosal IgA Ab response. Soon after i.v. challenge, Ag was detected within the epithelial cells of the small intestinal crypts and to a lesser degree within the epithelial cells higher up the villi, paralleling the gradient in expression of the polymeric Ig receptor and the transport of its ligand, oligomeric IgA. Uptake of Ag into the epithelial cells occurred only from the basolateral aspect and only when Ag complexed to IgA Ab could be present in the lamina propria. The results support the concept that local IgA Abs can excrete Ags from the body by transporting them directly through mucosal epithelial cells, using the same mechanism that transports free IgA into the mucosal secretions.     

Development of the excretory system in a polyplacophoran mollusc: stages in metanephridial system development

ABSTRACT: BACKGROUND: Two types of excretory systems, protonephridia and metanephridial systems are common among bilaterians. The homology of protonephridia of lophotrochozoan taxa has been widely accepted. In contrast, the homology of metanephridial systems -- including coelomic cavities as functional units -- among taxa as well as the homology between the two excretory systems is a matter of ongoing discussion. This particularly concerns the molluscan kidneys, which are mostly regarded as being derived convergently to the metanephridia of e.g. annelids because of different ontogenetic origin. A reinvestigation of nephrogenesis in polyplacophorans, which carry many primitive traits within molluscs, could shed light on these questions. RESULTS: The metanephridial system of Lepidochitona corrugata develops rapidly in the early juvenile phase. It is formed from a coelomic anlage that soon achieves endothelial organization. The pericardium and heart are formed from the central portion of the anlage. The nephridial components are formed by outgrowth from lateral differentiations of the anlage. Simultaneously with formation of the heart, podocytes appear in the atrial wall of the pericardium. In addition, renopericardial ducts, kidneys and efferent nephroducts, all showing downstream ciliation towards the internal lumen, become differentiated (specimen length: 0.62 mm). Further development consists of elongation of the kidney and reinforcement of filtration and reabsorptive structures. CONCLUSIONS: During development and in fully formed condition the metanephridial system of Lepidochitona corrugata shares many detailed traits (cellular and overall organization) with the protonephridia of the same species. Accordingly, we suggest a serial homology of various cell types and between the two excretory systems and the organs as a whole. The formation of the metanephridial system varies significantly within Mollusca, thus the mode of formation cannot be used as a homology criterion. Because of similarities in overall organization, we conclude that the molluscan metanephridial system is homologous with that of the annelids not only at the cellular but also at the organ level.     

Renal vasculature and excretory system of the agamid lizard,Ctenophorus ornatus

The structure and ultrastructure of the vasculature and nephric tubules of the kidney of the Ornate Dragon Lizard, Ctenophorus (=Amphibolurus) ornatus, was investigated by light microscopy and scanning electron microscopy of resin casts. Compared with other agamid lizards, the arterial supply of only two arteries per kidney is small. The number of glomeruli per kidney in C. ornatus, at between 400 and 600, is low by reptilian standards and very low for lizards. The glomeruli are not only comparatively few in number but are also simple in the nature of their capillary configuration. These features are suggestive of a greatly reduced surface area for arterial filtration. In contrast to the small arterial supply, the afferent venous supply, the renal portal system (RPS), is substantial and forms an extensive capillary network throughout the kidneys. No venous shunts were found in the kidneys, suggesting that the venous network is functioning as a true portal system. Valves were not identified within the RPS, implying that neural control of general vascular tone could alter velocity and perhaps the direction of blood flow by changing pressure profiles. The nephroi are comparatively short and display features consistent with the production of urate precipitates as the primary nitrogenous waste product. A close association between the distal tubule (DT) and the glomerular hilus may demonstrate a simple form of a juxtaglomerular apparatus. The finding of aglomerular tubules indicates an important role for tubular secretion. The results of this study indicate that these lizards may have a reduced reliance on filtration for homoiostasis and a greater reliance on tubular secretion. © 1993 Wiley-Liss, Inc.     

Antigenic profile of the human lacrimal gland.

The antigenic profile of 13 normal formalin-fixed, paraffin-embedded human main and accessory lacrimal glands, biopsied from patients aged 11 to 78 years, was studied using a panel of 27 polyclonal and monoclonal antibodies. Secretory cells of lacrimal acini reacted with antibodies to S-100 protein and simple epithelium-type cytokeratins CK 7, CK 8, CK 18, and CK 19. Their luminal membranes were labeled with antibodies to carcinoembryonic antigen, epithelial membrane antigen, and epithelial glycoproteins recognized by Ber-EP4. Myoepithelial cells were often immunopositive for S-100 protein, vimentin, glial fibrillary acidic protein (GFAP), and alpha-smooth muscle actin. More rarely, they reacted with antibodies recognizing CK 5, CK 13, and CK 14, which consistently labeled the basal cells of lacrimal ducts. Unlike myoepithelial cells, basal ductal cells were immunopositive for CK 7, CK 8, CK 18, and CK 19. In main excretory ducts, dendritic melanocyte-like cells co-expressing vimentin and S-100 protein intermingled with ductal epithelial cells. The luminal cells of lacrimal ducts basically paralleled secretory cells in their antigenic profile, although they lacked Ber-EP4 and were immunopositive for CK 4. Antibodies to neuron-specific enolase and synaptophysin reacted with nerve fibers among negatively reacting secretory acini. This antigenic profile closely parallels that of salivary glands and provides a basis for studies of lacrimal gland pathology.     

Properties of the V-type ATPase from the excretory system of the usherhopper,Poekilocerus bufonius

The bafilomycin A(1) and N-ethylmaleimide (NEM)-sensitive (V-type) ATPase was partially purified from the apical membrane-rich fractions of excretory system (Malpighian tubules and hind gut) of P. bufonius. Enzymatic activity was inhibited by bafilomycin A(1) (IC(50) = 1.3 nM) and NEM (IC(50) = 10.1 microM). The V-type ATPase activity is confined to the apical membrane fraction, while the activity of Na(+)/K(+) -ATPase forms the major part of the basal membrane fraction. The optimal pH required for maximal activity of V-type ATPase was pH 7.5. The effect of 30 mM of various salts on ATPase activity was investigated. NaCl and KCl caused increases of 175% and 184%, respectively. Other chloride salts also caused an increase in activity in the following ascending order: RbCl, LiCI, choline Cl, NaCI, KCl and tris-HCl. The activity of V-type ATPase was stimulated by a variety of different anions and cations, and HCO(3)(-) was found to be the most potent cationic activator of ATPase activity. The present results show that the properties of V-type ATPase of P. bufonius are similar to those reported for other insect tissues.     

The structure of the excretory system of the infective larva of Haemonchus contortus

The excretory system of the infective larva of Haemonchus contortus consists of a tubular H-system with two excretory cells. The excretory cells contain electron-dense granules which may be a source of exsheathing fluid. Video microscopy indicates that the pulsation of the excretory ampulla is due to a cycle of filling and emptying controlled by the excretory valve. The apparent functional similarity between this system and the contractile vacuole complex of protozoa is discussed.