Normal human macula densa morphology and cell turnover: A histological, ultrastructural, and immunohistochemical investigation.

The aim was to analyze the morphology of normal human macula densa (MD), evaluate the cells that may be responsible for its turnover, and collect quantitative data. Of four samples of normal human renal tissue, two were embedded in resin to measure the longitudinal extension and examine the ultrastructure of the MD, the other two were embedded in paraffin to study apoptosis and cell proliferation. The MD is composed of a monolayer tissue about 40 µm long, which includes 35-40 cells arranged in overlapping rows. Ultrastructurally, MD cells show two polarized portions: an apical end, with sensory features, and a basolateral aspect, with paracrine function. MD cells are connected apically by tight junctions, with/without adherens junctions, which form a barrier between the distal tubule lumen and the interstitium. Cells in degeneration, often associated with macrophages, and undifferentiated cells were found in the MD and adjacent distal tubule. A filamentous mat previously described in proximal tubule scattered tubular cells (STCs) was detected in the basal cytoplasm in undifferentiated cells. The tissue was consistently negative for the proliferation marker Ki67 and for the apoptotic markers caspase-3 and caspase-9. This work confirms our earlier morphological findings and provides new data: (a) MD cells display both apical adherens and tight junctions, the latter forming a tubulo-mesangial barrier; (b) the MD is a monolayer made up of about 40 cells arranged in rows; (c) the simultaneous presence of degenerating (8-13%) and undifferentiated (4-13%) cells reminiscent of STCs suggests a non-negligible cell turnover.

Renin secretion: an anatomical basis for tubular control.

By means of electron microscopy of serial sections and three-dimensional reconstruction of the juxtaglomerular apparatus a quantitative study has been made of the distribution of the areas of contact between the tubular and vascular components. Of the two arterioles the efferent is the only one consistently in contact with the distal tubule. The extraglomerular mesangium is also in contact with the distal tubule in all the apparatuses examined. Two morphologically distinct types of contact are described; one is thought to be permanent and the other reversible. An analysis of the cells of the juxtaglomerular apparatus for their position, granularity, and contact has revealed that the majority of granular cells are not in contact with the distal tubule. The anatomical findings are integrated in a model of the control of renin secretion based on variations in contact between the elements of the juxtaglomerular apparatus.

The renin-angiotensin system in nonmammalian vertebrates.

The most primitive components of the RAS appeared early in the phylogenetic history of vertebrate animals. It is probable that renin granules were present in the kidneys of ancestral chordates before divergence in the evolution of actinopterygian fish and tetrapods occurred. Granulated juxtaglomerular cells similar to the renin-containing cells of the mammalian nephron are found in most extant vertebrate species although not in agnathan and elasmobranch fish. A macula densa occurs in amphibians, birds and mammals; and an extraglomerular mesangium, only in birds and mammals. Renin-like activity and angiotensin-like pressor material have been demonstrated in all classes of vertebrates. The amino acid sequences of native ANG I have been determined for representative species of teleost fish, amphibian, reptile and bird. These peptides differ from mammalian angiotensins at positions 1, 5 and 9. The RAS appears to be involved in osmoregulation, ionoregulation and the control of blood circulation. Prolonged hypovolemic hypotension or sodium depletion increases renin levels. Angiotensins elicit drinking and stimulate transepithelial ion transport. However, direct steroidogenic and antidiuretic hormone-releasing activities, which would promote mineral and fluid conservation, have not been demonstrated unambiguously in nonmammalian vertebrates. ANG II raises blood pressure by direct vasoconstrictor action on arteriolar muscles in some animals, but perhaps more generally by acting on the nervous system and adrenal paraneurons. In birds the hormone also has a hypotensive effect. ANG II stimulates the SNS in agnathans, elasmobranchs, teleosts, amphibians, reptiles, birds and mammals. Thus, modulation of sympathetic activity may be one of the most primitive and conservative functions of the RAS. For this reason, nonmammalian vertebrates are valuable models for studying the neurogenic actions of angiotensin II relevant to hypertensive disease.

Cyclooxygenase-2 is associated with the macula densa of rat kidney and increases with salt restriction.

The kidney is a rich source of prostaglandins. These eicosanoids, formed by cyclooxygenase-dependent metabolism of arachidonic acid, are important physiologic mediators of renal glomerular hemodynamics and tubular sodium and water reabsorption. Two separate isoforms of cyclooxygenase (COX) have now been identified: constitutive COX-1, encoded by a 2.8-kb mRNA, and mitogen-activated COX-2, encoded by a 4.0-4.5-kb mRNA. COX-2 expression increases during development and inflammation, but, except for brain, constitutive expression is low. It has been generally accepted that physiologic renal production of prostaglandins is mediated by COX-1. However, in the absence of inflammation, low levels of COX-2 mRNA are also detectable in the kidney. To examine the role of COX-2 in the kidney and determine its intrarenal localization, we used a 1.3-kb cDNA probe specific for the 3' untranslated region of rat COX-2 and COX-2-specific antiserum. The COX-2-specific cDNA probe hybridized with a 4.4-kb transcript in total RNA from adult rat kidney. Immunoblots of microsomes isolated from kidney cortex and papilla indicated immunoreactive COX-2 in both locations. In situ hybridization and immunohistochemistry indicated that renal cortical COX-2 expression was localized to the macula densa of the juxtaglomerular apparatus and to adjacent epithelial cells of the cortical thick ascending limb of Henle. In addition, COX-2 immunoreactivity was detected in interstitial cells in the papilla. No COX-2 message or immunoreactive protein was detected in arterioles, glomeruli, or cortical or medullary collecting ducts. When animals were chronically sodium restricted, the level of COX-2 in the region of the macula densa increased threefold (from 0.86 +/- 0.08 to 2.52 +/- 0.43/mm2) and the total area of the COX-2 immunoreactive cells in cortex increased from 34 microns2/mm2 of cortex to 226 microns2/mm2 of cortex. The intrarenal distribution of COX-2 and its increased expression in response to sodium restriction suggest that in addition to its proposed role in inflammatory and growth responses, this enzyme may play an important role in the regulation of salt, volume, and blood pressure homeostasis.

Anatomical relationship between kallikrein-containing tubules and the juxtaglomerular apparatus in the human kidney.

Current evidence suggests a functional and biochemical link between the renin and the kallikrein systems. The purpose of this work was to study the localization of kallikrein along the human nephron to elucidate whether there exists an anatomical base for such interrelation. Serial sections of human kidney tissue were stained by immunocytochemical methods with antisera against kallikrein. Kallikrein immunostaining was observed exclusively in segments of the distal nephron lying in the cortical labyrinths and forming arcades in its distal portion. Consistently the tubules containing kallikrein established a close anatomical relationship with the afferent arteriole of the juxtaglomerular apparatus providing an anatomical base for an interaction between the renin and kallikrein systems in the human kidney.

Mammalian renal modifications in dry environments.

The literature on the role of the kidney and renal morphological modifications in places of limited water supply is reviewed. The anatomical structures for urine concentration found in animals living in desert or arid environments, although not all occurring in one particular animal, are wide medullae, long loops of Henle, long proximal tubules, long collecting tubules, small renal corpuscles, extension of the renal pelvis, well developed elongated papillae, occurrence of giant vascular bundles, specialized ultrastructure of Henle's loops, epithelial changes in the collecting tubule, zonation of the vasa recta and peculiarity of the arterial supply to the kidney. The renal renin content is moderately high in these species. The renin-angiotensin-aldosterone system is very active, retaining Na+ with water. The urine is concentrated at the expense of other electrolytes. Both the renal blood and urinary flow rates are lower than in species with access to unlimited water supply. The juxtaglomerular apparatus components are topographically intimate for effective tubuloglomerular autoregulation of renal blood flow.

[Modification of Bowie's method of demonstrating specific granules in cells of the human renal juxtaglomerular apparatus fixed in neutral formalin]. / Modifikatsiia metoda Bovi dlia vyiavleniia spetsificheskikh granul v kletkrakh iukstaglomeruliarnogo apparata pochek cheloveka, fiksirovannykh v neitral'nom formaline

A modification of Bowie's method for detection of specific granules of the juxtaglomerular apparatus of the human kidneys, fixed in 10% neutral formalin, is suggested. In order to achieve better staining, sections of material fixed in formalin are additionally treated with Helly's liquid and, following the removal of sublimate deposit, with a 2.5% solution of potassium bichromate. After this the sections are stained by Bowie's method in accordance with Pitcock and Hartroft's prescription.

[Morphometric study of the normal kidney and in pathology: the possibilities and limitations]. / Morfometricheskoe izuchenie pochki v norme i pri patologii: vozmozhnosti i ogranicheniia.

The possibilities of morphometry in the study of normal and pathologically altered kidney at the macroscopical, light optical and ultrastructural levels are considered. Morphometrical approaches to the examination of the glomeruli, nephron canaliculi and collecting tubules, blood and lymph vessels, juxtaglomerular apparatus, interstitial medulla cells, intraorgan nerves are analysed. Some practical recommendations for quantitative analysis of the renal structure are given, the causes of possible errors are indicated.