Immunohistochemical localization of tonin in rat salivary glands and kidney

Secretion by striated ducts of mammalian major salivary glands: review from an ultrastructural, functional, and evolutionary perspective

In addition to their role in electrolyte homeostasis, striated ducts (SDs) in the major salivary glands of many mammalian species engage in secretion of organic products. This phenomenon usually is manifested as the presence of small serous-like secretory granules in the apical cytoplasm of SD cells. The composition of these granules is largely unknown, except in the case of the cat and rat submandibular gland, where the granules have unequivocally been shown to contain kallikrein. In some species, the apical cytoplasm of SD cells contains variable numbers of vesicles, both spherical and elongated, that vary in appearance from 'empty' to moderately dense. In the rat parotid gland, lucent vesicles transport glycoproteins to the luminal surface where they are incorporated into the apical plasmalemma and the glycocalyx. There is a strong possibility that in various species some of these vesicles are involved in transcytosis of antibodies to the saliva from their source (plasma cells) in the surrounding connective tissue. In addition, vesicles may engage in transfer of growth factors from the saliva to the interstitium. In a few species, conventional SDs have been replaced by ducts that are wholly given over to secretion, i.e., they entirely lack basal striations; although such ducts occupy the histological position of conventional SDs, it is not clear whether they represent a new type of duct or merely are modifications of SDs. Broad-based comparisons of ultrastructural and other data about SDs offer some insight into evolutionary history of salivary glands and their role in the adaptive radiation of mammals. Evolutionary patterns emerged when we made interspecific comparisons across mammalian orders. Among the bats, there is a clear relationship between SD secretion and general categories of diet.

Comparative study of renin-containing cells. Histological approaches

The juxtaglomerular apparatus is known to be the functional unit of renin control. In the present review, the author will describe the comparative characteristics of renin-containing (RC) cells as well as extrarenal distribution, paying special attention to developmental and topographical approaches. The characteristic locality of RC cells suggests that the secretion of renin is performed at a site beside the adventitia or via the glomerular capillaries. Ontogenetical and phylogenetical investigations of RC cells have provided interesting findings on their morphogenesis. Analysis of the endocrine kidney after unilateral obstruction of the ureter provides some findings about the origin of RC cells and the processing of renin granules. Observation of developing adrenal renin suggests that there is important involvement of angiotensin II produced by renin synthesis in the morphogenesis of the adrenal gland in the fetal stage. Coagulating gland (CG) renin is characterized by testosterone-regulated and exocrine mechanisms. Recently, all or some of the components of the renin-angiotensin system (RAS) have been reported to be synthesized and secreted outside of classical organs or tissues. In the future, the real function of local RAS will be clarified by using gene targeting in mice.

Comparisons of the densities of NADPHd reactive and nNOS immunopositive neurons in the hippocampus of three age groups of young nonhandled and handled rats

The complete absence of handling of male rats during neonatal development (from birth to postnatal day 21) correlates with an impairment of latent inhibition [J. Feldon, I. Weiner, From an animal model of an attentional deficit towards new insights into the pathophysiology of schizophrenia, J. Psychiatr. Res. 26 (1992) 345-366.]. Such nonhandling of rats reportedly also correlates with a decreased expression of reduced nicotinamide adenine dinucleotide phosphate-diaphorase (NADPHd) reactivity in the hippocampus in adult rats (6 months of age) when compared with rats of the same age that were handled during the same neonatal period [R.R. Vaid, B.K. Yee, U. Shalev, J.N. Rawlins, I. Weiner, J. Feldon, S. Totterdell, Neonatal nonhandling and in utero prenatal stress reduce the density of NADPH-diaphorase-reactive neurons in the fascia dentata and Ammon's horn of rats, J. Neurosci. 17 (1997) 5599-5609.]. The present study investigated whether such a decrease in NADPHd activity would be detectable at earlier ages. Therefore, the present study assessed the density of nitric oxide (NO) producing neurons in the fascia dentata and Ammon's horn in 28-, 54-, and 118-day-old nonhandled and handled male rats using NADPHd histochemistry and immunohistochemical localization of neuronal isoform of nitric oxide synthase (nNOS), a NADPHd. This showed that in these three age groups, the numbers of NADPHd positive neurons per unit area throughout the hippocampus of rats that received no handling during neonatal development did not differ significantly from those of rats that received regular daily handling. In addition, we found in the rats of 118 days of age that the areal density of nNOS immunopositive neurons in the hippocampus also did not differ significantly between nonhandled and handled rats. Nevertheless, in a parallel study, rats from the same experimental group receiving identical treatments showed the expected impairment of latent inhibition at 4 months of age [R. Weizman, J. Lehmann, S. Leschiner, I. Allmann, T. Stoehr, C. Heidbreder, A. Domeney, J. Feldon, M. Gavish, Long-lasting effect of early handling on the peripheral-type benzodiazepine receptor, Pharmacol. Biochem. Behav. in press.]. These results suggest that nonhandling of rats during the early neonatal period, that does result in impairment in latent inhibition, does not affect the numbers of NO producing neurons in the hippocampus in rats of young ages, including the age of observed impairment of latent inhibition.

Distribution of tonin- and kallikrein-like activities in rat brain

Tonin- and kallikrein-like activities were investigated in different regions of the rat brain. The highest values of specific tonin activity, expressed as picomoles of angiotensin II liberated per minute per milligram of protein, were found in the neurohypophysis (359 +/- 190) and in the archicerebellum (200 +/- 68). The highest level of total tonin activity (picomoles of angiotensin II liberated per minute) was observed in the archicerebellum (902 +/- 308) which retained 97% of total tonin activity of whole cerebellum. Tonin activity was not detected in the cortex of cerebellum and in the choroid plexus. Low to intermediate values of specific (1.09 +/- 0.33 to 5.32 +/- 2.37) and total (1.38 +/- 0.55 to 93.00 +/- 49.30) tonin activity were observed in adenohypophysis, cerebellar nuclei, hypothalamus, thalamus, midbrain, pons, medulla and neurohypophysis. The lowest values of specific (0.11 +/- 0.05) and total (0.69 +/- 0.31) activities were observed in the hippocampus. Kallikrein-like activity was expressed as picomoles of p-nitroaniline liberated per minute per milligram of protein. No activity was detected in the neurohypophysis. For other regions, the values of the specific activity ranged between 72 +/- 18 and 282 +/- 14 except for the choroid plexus which was 5 +/- 2. The total kallikrein activity was also homogeneous ranging from 330 +/- 100 to 1870 +/- 112. For the choroid plexus and adenohypophysis the total kallikrein activity was 2.0 +/- 0.8 and 27 +/- 11, respectively.

Identification of tonin in brain and exocrine tissues and in the cell-free translation products encoded by the mRNA of these tissues

Tissue-specific expression of the esteropeptidase tonin [EC 3.4.99.-] was investigated in rat brain, submandibular gland, pancreas and kidney. Specific polyclonal and monoclonal antibodies to purified rat tonin from the submandibular gland have been developed and characterized and have been purified via a tonin-agarose affinity column. Immunoreactive tonin was measured by a recently developed tonin direct radioimmunoassay using a rabbit tonin antiserum. Resulting tonin levels were found to be 105.27 +/- 2.71 micrograms/mg (of protein) in submandibular gland, 3.18 +/- 0.32 ng/mg in pancreas, 1.35 +/- 0.08 ng/mg in kidney and 0.12 +/- 0.01 ng/mg in brain (means +/- S.E.M.). Western-blot analysis shows that affinity-purified anti-tonin antibody binds to a 32,000-Mr protein from brain and submandibular-gland extracts. The protein, a tonin precursor, was identified from cell-free translation products directly by polyadenylated [Poly(A)+]mRNA species in a wheat-germ system. After the translation products were subjected to immunoprecipitation with affinity-purified tonin antibody, SDS/polyacrylamide-gel electrophoresis of these precipitates revealed two precursors of tonin, with Mr values of 30,000 and 29,000, which are encoded by brain and submandibular-gland mRNA; however, only the 30,000-Mr preprotonin was encoded by pancreas and kidney mRNA. Collectively, the data show that tonin exists in brain, submandibular gland, pancreas and kidney, and can be synthesized by the mRNA of these tissues.

Rat urinary kallikrein localization in kidney: effects of fixation

The influence of fixation on the immunocytochemical localization of tissue kallikrein in the kidney has been evaluated using both monoclonal and polyclonal antibodies. These studies have provided several results relevant to kallikrein localization in kidney: (1) the intensity and distribution of immunostaining with both polyclonal and monoclonal anti-kallikrein antibodies is fixation-dependent; (2) the most intense and consistent localizations of kallikrein are in the connecting tubule and the cortical collecting duct of the nephron; (3) kallikrein-like immunoreactivity is seen in proximal tubules with polyclonal but not with non-cross-reactive monoclonal antibodies; and (4) fixatives which disrupt membranes reveal a kallikrein-like antigen in straight tubules of the outer medulla. However, immunostaining with monoclonal antibodies indicates that much of the observed immunostaining at this site probably represents cross-reactivity with another member of the kallikrein family of enzymes.

Rat submaxillary gland serine protease, tonin. Structure solution and refinement at 1.8 A resolution

Tonin is a mammalian serine protease that is capable of generating the vasoconstrictive agent, angiotensin II, directly from its precursor protein, angiotensinogen, a process that normally requires two enzymes, renin and angiotensin-converting enzyme. The X-ray crystallographic structure determination and refinement of tonin at 1.8 A resolution and the analysis of the resulting model are reported. The initial phases were obtained by the method of molecular replacement using as the search model the structure of bovine trypsin. The refined model of tonin consists of 227 amino acid residues out of the 235 in the complete molecule, 149 water molecules, and one zinc ion. The R-factor (R = sigma Fo - Fc/sigma Fo) is 0.196 for the 14,997 measured data between 8 and 1.8 A resolution with I greater than or equal to sigma (I). It is estimated that the overall root-mean-square error in the coordinates is about 0.3 A. The structure of tonin that has been determined is not in its active conformation, but one that has been perturbed by the binding of Zn2+ in the active site. Zn2+ was included in the buffer to aid the crystallization. Nevertheless, the structure of tonin that is described is for the most part similar to its native form as indicated by the close tertiary structural homology with kallikrein. The differences in the structures of the two enzymes are concentrated in several loop regions; these structural differences are probably responsible for the differences in their reactivities and specificities.

Anatomy of the renin-angiotensin system in the normal and pathological kidney

In this review we describe the contributions made by immunocytochemistry to our knowledge of the renin-angiotensin system in the normal and the pathological kidney. Most of the renin-secreting cells appear to be on the outer aspect of the vessel wall, supporting the view that renin is secreted mainly into the interstitium of the kidney rather than into the lumen of the vessel. Angiotensin II immunoreactivity is present within renin-secreting cells. The angiotensin II appears to be present in high concentration in the renin storage granules and is therefore presumably secreted from the cell with renin. The pathways by which renin is secreted from the cell have also been clarified. In pathological kidneys, the reactions of renin-secreting cells to variation in functional demand have been confirmed. Renin-containing cells have also been found in most types of renal tumours and occasional cases probably secrete renin or prorenin into the blood. In renal tumours and in the developing kidney (in all species studied) the renin-containing cells are also intimately associated with blood vessels.

Comparative studies on the localization of esteroproteases and kallikrein-like activity in primate organs

Various organs of three species of monkey were screened histochemically for esteroproteases using N-acethyl-L-methionine-alpha-naphthylester (alpha N-O-met) as the substrate and also for enzymes with kallikrein-like activity using D-Val-Leu-Arg-4-methoxy-2-naphthylamide as the substrate. Characteristic differences were found in the localization of the reaction products obtained with both substrates. In the main salivary glands, esteroproteases (alpha N-O-met reactivity) were found in mucous cells (submandibular gland), intercalated duct cells (parotid gland), acinar cells (sublingual gland), striated and interlobular duct cells (all glands). They were also localized in superficial lining epithelial cells of the digestive system, in liver cells, and acinar cells of the pancreas. Enzymes with kallikrein-like activity were found only in the striated and interlobular duct cells of salivary glands, in acinar cells of the pancreas, and in proximal tubular cells of the kidney. Free cells (including mast cells) normally distributed in the connective tissue of various organs showed reactivity towards alpha N-O-met. Some of these cells were also reactive against Val-Leu-Arg-4-MNA.

Immunohistochemistry of tonin in rat submandibular gland during development, lactation and secretion

Tonin is a serine protease found in high concentrations in the submandibular gland (SMG) of the adult rat where it has been localized by immunohistochemistry in the granular ducts. The present study examined the development of tonin in the SMG, the effect of lactation and of stimulation of tonin release, using the peroxidase-antiperoxidase technique and antitonin. Tonin-like immunoreactivity first appeared in the primitive striated duct of the SMG on day 19 foetal and increased in intensity as the ducts developed into granular ducts. Reaction product in granules was seen on day 17 postpartum. Its localization within granules was established by immunochemistry of Sepharose beads to which had been coupled the contents of granules isolated from adult rats. The granular ducts of female rats, which are less developed than in the male, showed a marked increase in tonin-immunoreactivity during lactation. Stimulation of tonin secretion by isoprenaline caused massive discharge of tonin-like immunoreactivity into the lumen of the granular ducts during in vitro incubation. However, within one hour complete regranulation was apparent. The secretion was prevented by propranolol. The results indicate that tonin or a tonin-like substance appears in the rat submandibular gland late in gestation in ducts that presumably develop into granular ducts where it is found in abundance in granules in the adult, that the amount in females is increased during lactation, and that most of the granules are discharged during stimulation, only to be rapidly replaced.

Extrarenal angiotensin-forming enzymes

There are two types of enzymes in tissues leading to angiotensin formation: a) those resulting in the formation of angiotensin I, such as renin and cathepsin D, the presence of which is now well established for brain tissue and b) Those leading to the direct formation of angiotensin II without the angiotensin I step, such as cathepsin G and tonin. Recent findings concerning tonin, a serine protease, are described: a) 80% of its amino acid sequence, b) its different characteristics from other serine proteases, from renin, cathepsin D and the angiotensin I converting enzyme, c) the activation of inactive renin, d) its involvement in the 1K-1C hypertensive rats, e) the demonstration of its presence in the distal tubular cells of the rat kidney, and finally, f) its presence in urine and the influence of age and of sodium intake on its urinary excretion.