The juxtaglomerular apparatus in the avian kidney

Summary The domestic fowl has two types of glomerulus (mammalian and reptilian type). 30 of each were studied morphometrically in semi thin and PAS-stained sections. The juxtaglomerular apparatus was larger in the mammalian type, but complete in both, containing macula densa, Goormaghtigh (lacis) cells and hilar arterioles. Granular epithelioid cells were occasionally found in the afferent arterioles and within the glomerulus in the mammalian type only.All glomeruli studied had a prominent mesangial cell mass (MCM), which was larger in mammalian type glomeruli. Hilar arterioles often penetrated the mesangial cell mass and regularly ramified within it. There was always extensive direct contact between the Goormaghtigh cell mass and the macula densa on the one side and the MCM on the other. In mammalian type glomeruli, the afferent arterioles were invariably found centrally within the MCM, but in the reptilian type no distinct pattern was found. The close relationship between the MCM and the hilar arterioles, especially in mammalian type glomeruli, suggests that the MCM regulates the glomerular filtration rate.     

Development and fate of the secretory granules of juxtaglomerular epithelioid cells

Summary The development and fate of the secretory granules in murine, rat and human juxtaglomerular epithelioid cells were examined using ultrastructural and immunocytochemical methods. The formation of mature renin granules occurs by fusion of rhomboid protogranules followed by coalescence of their paracrystalline contents, and by the fusion of roundish juvenile granules having an amorphous internum. Protogranules with paracrystalline contents are prominent in animals with stimulated renin synthesis, indicating an overcharge in processing and/or packaging of the secretory product, renin, under these conditions. Various similarities between lysosomes/multivesicular bodies (MVBs) and juvenile renin granules have been observed. With the exception of small MVBs, no renin-negative organelles that could be regarded as lysosomes were found in epithelioid cells of mice and rats. Therefore, we suggest that renin granules are modified lysosomes. Immunocytochemical findings indicate that juvenile secretory granules of epithelioid cells represent the converting and activating compartment for prorenin. Endocytosed foreign tracers such as HRP or cationized ferritin are preferentially internalized by juvenile renin granules, which hence appear to be outstanding by their fusogeneity. Consequently, juvenile granules are probably responsible for the secretion of prorenin, and mature granules for that of active renin.These studies were supported by the German Research Foundation within the Forschergruppe Niere/Heidelberg     

Ultrastructural changes associated with renin secretion from the juxtaglomerular apparatus of mice

Summary Thin sections and freeze-fracture replicas were used to investigate the ultrastructural changes associated with renin secretion from the juxtaglomerular part of the afferent arteriole of male mice. Adrenalectomized animals in which renin secretion was stimulated by furosemide application and bleeding were also studied. Exocytosis of mature electron-dense granules was found in all experimental groups. Before extrusion, the region of granule facing the cell membrane changed, with vesicular and/or stacked membrane-like profiles and a small local protrusion of the granule membrane appearance of. Concomitantly, punctuate sites of fusion between the cell and granule membranes were observed. Later, unaltered amorphous, and altered membrane-like granule content was released from omega-shaped cavities into the extracellular space. In stimulated animals the alteration and extrusion of several closely apposed granules was reminiscent of compound exocytosis. Coated pits were frequently seen, suggesting specific retrieval of the former granule membrane. The collapsing silhouette of a depleted granule very rarely took the form of a saccule whose narrow membrane-bounded neck was continuous with the extracellular space.Observed were two additional events by which active and inactive renin may be released. Small electron-lucent vacuoles of undetermined origin fused with the cell membrane and, in stimulated kidneys, some epithelioid cell processes disintegrated. However, the interpretation of the related ultrastructural phenomena was uncertain.These studies were supported by the German Research Foundation within the SFB 90 Cardiovasculäres System     

Studies on the juxtaglomerular apparatus

The vascular pole of the juxtaglomerular apparatus in Tupaia belangeri was studied with special reference to the intercellular contacts of the periendothelial cells and the endothelium of the vas afferens. The periendothelial cells of the vascular pole of the glomerulum are connected by numerous gap junctions; and the granulated epithelial cells are suggested to form a functional unit. Probably there is a continuity of this system throughout the entire vascular pole including (1) all granulated cells, (2) all lacis cells, (3) the mesangium cells and (4) the adjacent smooth muscle cells of the vas afferens and vas efferens. Analysis of the endothelial junctions shows a zonular arrangement of tight junctions indicating a rather tight blood-tissue barrier next to the glomerular vascular pole; The ultrastructure of the different cell types of the vas afferens is also described, emphasizing the granulated epithelial cells and their innervation.     

Ultrastructural and morphometric aspects of the juxtaglomerular apparatus in the monkey kidney

Summary The authors describe the ultrastructure of the juxtaglomerular apparatus in five adult male Cebus apella monkeys and communicate morphometric data of the macula densa.In comparison with several species of rodents examined before, the macula cells of the monkey contain many more mitochondria and possess a particularly thick basal membrane. The relative volume of the nuclei is slightly smaller than in rodents.The Goormaghtigh cells of the monkey resemble those of the other animals investigated.The epithelioid (or juxtaglomerular) cells do not contain secretory granules. This observation reminds one of the behavior of the epithelioid cells of guinea pigs.Dedicated to Professor Dr. med. G. Petry (Marburg/Lahn) on the occasion of his 65th birthdayThe authors wish to thank Professor Dr. G. Peters, Head of the Institute of Pharmacology, and Professor Dr. F. Roch-Ramel for kindly having provided the monkey kidneys     

Morphogenesis of the renal juxtaglomerular apparatus and peripolar cells in the sheep

Summary The morphogenesis of the juxtaglomerular apparatus and peripolar cells was studied in the metanephros of fetal sheep (from 24 to 147 days of gestation) using light and electron microscopy. The first juxtaglomerular apparatus was detected at 45 days of gestation, following constriction of the edges of Bowman's capsule and formation of the vascular pole of the renal corpuscle. Mesenchymal cells gave rise to lacis cells and to smooth muscle and epithelioid cells of the juxtaglomerular arterioles. Epithelioid cells developed only sparse cytoplasmic granulation, first detectable at 92 days. The macula densa developed from tubular cells at the junction of the middle and upper limbs of the S-shaped body of the developing nephron. Peripolar cells arose from epithelial cells in the lower limb of the S-shaped body, at the constricting edges of Bowman's capsule, and formed a cuff around the origin of the glomerular tuft. Cytoplasmic granules were first detected in peripolar cells at 53 days, and remained more prominent than epithelioid cell granulation throughout gestation.     

Processing endopeptidase deficiency in neurohypohysial secretory granules of the diabetes insipidus (Brattleboro) rat

The homozygote Brattleboro rat exhibits a hereditary diabetes insipidus due to a deficiency of vasopressin, the antidiuretic hormone. It has previously been shown that in this animal a single nucleotide deletion in the provasopressin gene leads to a mutant precursor with a C-terminal amino acid sequence different from that of the wild-type. However the N-terminal region including the hormone moiety, the processing signal as well as the first two-thirds of the neurophysin is entirely preserved and absence of maturation has to be explained by an additional cause. We show here that the neurohypophysis of the homozygote Brattleboro rat, in contrast to the adenohypophysis, displays a significant decrease in the Lys-Arg processing endopeptidase activity when compared to the heterozygote or the wild-type Wistar. It is suggested that hypothalamic vasopressinergic neurons of the homozygote Brattleboro rat display a deficiency in the processing enzyme in contrast to the oxytocinergic neurons in which processing of prooxytocin is normal.     

The morphology of the juxtaglomerular apparatus in the toad,Bufo bufo

Summary In a light microscopic study the course of the tubule in the kidney of the toadBufo bufo was studied. The distal tubule returning to the glomerulus of its origin appears to enclose the afferent arteriole. In that area, from which a three dimensional graphic reconstruction is made, there is an intimate contact between tubular and vascular wall. The latter contains granulated media cells. In the part of the tubule adjacent to the afferent arteriole an accumulation of nuclei is present. It is suggested that this structure is similar to the macula densa of the mammalian juxtaglomerular apparatus. The functional significance of a stricture in the tubule distally from the macula densa-like structure is discussed.The authors wish to thank Mrs. Ineke van de Mee-Wienen and Miss Ans Rouwenhorst for their technical assistance and Mr. J. J. M. de Bekker for the realization of the graphic reconstruction.     

Subcellular distribution of neurophysin in rats subjected to haemorrhage,salt-loading and lactation and in rats with hereditary diabetes insipidus (brattleboro strain)

Summary The subcellular distribution of radioactive neurophysin and the release of neurophysin from isolated neurosecretory granules (NSG) from the posterior pituitary gland were studied at various time intervals after injection of (³⁵S) cysteine into the supraoptic nucleus under various functional conditions. In consistency with previous findings (Norström, 1972), increased amounts of radioactive neurophysin were recovered extra-granularly at longer time intervals after isotope injection. Increased quantities of free labelled neurophysin were found in lactating rats and homozygous diabetes insipidus (DI) rats 7 and 1 day after injection, respectively. Salt-loading for 4 days did not affect the subcellular distribution of radioactive neurophysin 1 day after injection of (³⁵S) cysteine. 8.5 days after isotope injection acute haemorrhage was followed by augmented amounts of radioactive neurophysin among the soluble proteins, but at 1 day no difference was observed between bled animals and controls. The spontaneous release of neurophysin form NSG was higher in stimulated animals and increased with time after isotope injection in controls as well as in experimental animals. The absolute increase in release of neurophysin in response to ATP was higher in stimulated rats whereas NSG from DI rats did respond poorly to ATP.The present work was supported by grants from Svenska Livförsäkringsbolags nämnd för medicinsk forskning, Wilhelm och Martina Lundgrens fond, Albert Wallins fond and the University of Göteborg. I am indebted to Miss Gull Grönstedt for careful secretarial work.     

The morphological basis of fluid balance in the interstitium of the juxtaglomerular apparatus

Summary The morphological basis of fluid balance in the interstitium of the juxtaglomerular apparatus (JGA) was reevaluated in rats, mice and Tupaia. Three ultrastructural features in the region of the vascular pole of the renal corpuscle are described that may be important for the fluid balance in this region: (1) podocyte foot processes in the parietal layer of Bowman's capsule, (2) endothelial fenestrations in the wall of the incoming afferent arteriole, both facing Goormaghtigh and epithelioid cells, and (3) the mesangial type lining of the glomerular stalk. With respect to the relevant pressure gradients, this morphology may provide the basis of bulk-fluid flow directed to the interstitium of the JGA including the Goormaghtigh cell field. Thus, the fluid balance in the lacis area and, consequently, the tubulo-glomerular feedback mechanism, probably does not solely depend upon the reabsorptive transport of the macula densa. Similar considerations may be valid for the humoral control of renin secretion from juxtaglomerular epithelioid cells.These studies were supported by the German Research Foundation within the SFB 90 Cardiovasculäres System     

Ultrastructural studies on the secretory process in the epithelioid cells of the juxtaglomerular apparatus

The epithelioid cells of the juxtaglomerular apparatus have been studied with respect to the release mechanism of the secretory granules. Invaginations of the plasma membrane into the interior of the epithelioid cells are interpreted as stages before or after an exocytotic process. Granules are sometimes observed in close contact with the plasma membrane, and material with electron density similar to that of the granules can also be observed in the invaginations. These morphological features suggest that the granular material of the epithelioid cells is extruded into the texture of the basal lamina. Furthermore, a dense network of microtubules and microfilaments is described and the functional role of this system in exocytosis is discussed.     

Microtubular number in the tractus hypophyseus of newborn normal rats and newborn rats with congenital diabetes insipidus

Summary Evidence has already been adduced suggesting that an increase in microtubular number occurs in the tractus hypophyseus of rats stressed by the administration of hypertonic saline, and of rats with congenital diabetes insipidus (CDI). Since the tractus hypophyseus in these animals shows high secretory activity, it seems likely that the microtubular increase reflects the participation of microtubules in axoplasmic transport. To exclude, however, a congenital microtubular abnormality in CDI, affected newborn rats were examined. In these, the microtubular number was normal, thus suggesting that the increase in microtubular number seen in adult animals was not a congenital morphological abnormality. However, by 4 days of age there was a slight but statistically significant increase in microtubular number in affected rats, a change probably attributable to increased secretory activity.This project was supported by the Medical Research Council     

The juxtaglomerular apparatus in the mesonephros of Newt (Triturus cristatus)

Summary 1)As in mammals, the juxtaglomerular apparatus of the Newt (Triturus cristatus) is composed by cells of the media of the afferent glomerular arteriole and by cells of the intermediary tubule. 2) The cells of the media of the glomerular arteriole are of two different types: granular and agranular cells. 3) The intermediary tubule is formed by dark and light cells. 4) Part of interrenal body is located close to glomerular arteriole and intermediary tubule.This work was supported by grant of Consiglio Nazionale delle Ricerche of Italy (C.N.R.) N. 115/815/04677.     

Vasopressin and ethanol preference. II. Altered preference in two strains of diabetes insipidus rats and nephrogenic diabetes insipidus mice

In the first paper of this series, the influence of a single gene (di) for vasopressin deficiency on ethanol intake in rats was demonstrated. We studied preference for concentrations of ethanol between 2.2 and 10 percent versus tap water in Brattleboro rats homozygous for diabetes insipidus (di/di), heterozygous (di/+) or normal (+/+). The di/di rats, totally lacking in vasopressin, had greatly reduced preference scores for all concentrations of ethanol. Their intake of ethanol (g/day) was higher than heterozygotes or normals, but only when 2.2 percent ethanol was offered as a choice. Treatment with vasopressin or related peptides restored ethanol drinking to normal but also corrected water balance. In the experiments reported here, Roman High Avoidance (RHA) rats of three genotypes (+/+, di/+, and di/di) were also tested for ethanol intake and preference with similar but not identical results. Thus, the effects of the di gene are independent of the genetic background on which it is placed to at least some extent. Chlorothiazide, a drug unrelated to vasopressin, also normalized ethanol drinking and corrected water balance in di/di rats. In nephrogenic diabetes insipidus mice, there was a strong negative correlation between severity of polydipsia and preference for ethanol. Thus, no paradigm tested was effective in dissociating polydipsia from reduced ethanol preference and increased ethanol intake. While these results cannot exclude a possible regulatory role for endogenous vasopressin in ethanol preference drinking, they more strongly suggest that reduced preference for ethanol and increased ethanol intake are epiphenomena secondary to a polydipsic state.     

Immunohistochemical demonstration of renin in the juxtaglomerular apparatus of three Bufo species

Summary The cellular localization of renin was examined in the kidneys of some amphibians of the genus Bufo by immunoperoxidase and immunofluorescence techniques with an antiserum to renin isolated from the submandibular gland of the mouse. Immunoreactivity could be demonstrated in the media cells of the afferent arterioles (juxtaglomerular cells) close to as well as at great distance from the glomeruli. Occasionally, media cells of larger arterial vessels were also stained. The immunohistochemical data seem to be in accordance with earlier results obtained with a modified silver impregnation technique (Movat's staining procedure) used for the visualization of juxtaglomerular cells in non-mammalian vertebrates. Mouse kidney tissue, studied for purposes of comparison, showed renin-immunoreactivity as described by earlier investigators, i.e., immunoreactive staining in the afferent arterioles near the glomeruli and in the proximal tubule cells.     

Peripolar cell hypertrophy in the renal juxtaglomerular region of newborn sheep

Summary In the renal juxtaglomerular region of newborn sheep, it was found that glomerular peripolar cells and their granules were very much larger than those found in fetal lambs or adult sheep. Similar peripolar cell hypertrophy was triggered in fetal lambs treated in utero with intraperitoneal injections of dexamethasone. Ultrastructurally, granules of peripolar cells from newborn lambs resembled closely the enlarged zymogen granules described in the pancreas of newborn rats. Such peripolar cell hypertrophy may reflect a functional adaptation of the kidney to immediate postnatal life.     

Regional analysis of brain opiate receptors in rats with hereditary hypothalamic diabetes insipidus.

The regional distribution of stereospecific ³H-dihydromorphine binding sites in Brattleboro rats with hereditary hypothalamic diabetes insipidus was studied. Control animals were homozygous normal Brattleboro rats and rats heterozygous for the vasopressin deficiency. Scatchard plots of ³H-dihydromorphine binding in a washed membrane preparation showed that rats with diabetes insipidus exhibited higher receptor concentrations in all assayed areas of the cerebral hemispheres. In the diencephalon, receptor concentrations were lower in diabetes insipidus rats. The results point to the existence of interactions between brain opioid systems and neurohypophyseal peptides.     

Histochemistry of the juxtaglomerular apparatus in the toad Bufo bufo

Summary An investigation regarding the question of whether there exists a macula densa as part of the juxtaglomerular apparatus in the kidney of amphibians has been carried out. With the aid of a histochemical reaction for glucose-6-phosphate dehydrogenase activity, the presence of a macula densa zone as a specialized part of the distal tubule in the toad Bufo bufo was demonstrated. The functional significance of the high glucose-6-phosphate dehydrogenase activity in the macula densa cells is discussed.     

Appearance of dense granules in the rough endoplasmic reticulum of the juxtaglomerular cells in mice administered with captopril

Summary Captopril [1-(D-3-mercapto-2-methyl-1-oxopropyl)-L-proline (S,S)] is now known to be an inhibitor of angiotensin-converting enzyme. In male mice, the juxtaglomerular cells were examined by electron microscopy 42 h after administration of captopril. Numerous dense granules appeared in the rough endoplasmic reticulum of these cells.     

Synthesis and migration of proteins and glycoproteins in juxtaglomerular cells of sodium-deficient rats

Summary Sections of juxtaglomerular cells from sodium-deficient rats were subjected to radioautography after a single intravenous injection of L-tyrosine3,5 ³H or of L-fucose ³H to identify the sites of synthesis and to follow the migration of newly-formed proteins and glycoproteins. As early as 2 min after injection of L-tyrosine ³H, the label was highest in the rough endoplasmic reticulum (RER), suggesting that cisternal ribosomes are sites of protein synthesis. By 60 min, much of the label had migrated from the RER to the Golgi complex. Some radioactivity was already present over specific granules by 2 min but a peak was reached at 4h. The label over myofilaments was evident at all time intervals, indicating a certain incorporation of tyrosine into their contractile and/or structural proteins. The label over the cell surface peaked at 4h. After injection of L-fucose ³H, there was an early and important relative specific radioactivity in the Golgi complex at 5 min with a peak at 20 min and a decrease thereafter. The label increased slightly but steadily in secretory granules and cell surface to reach maxima at 4 h. A low level of radioactivity was recorded in mitochondria at all time intervals. After injection of both fucose ³H and tyrosine ³H, the label was detected at relatively low levels in the cytosol. These results suggest that renin, as the major secretory glycoprotein of juxtaglomerular cells, is synthetized in the RER, packaged in the Golgi complex and found relatively rapidly in newly-formed secretory granules. Part of the fucose and tyrosine labels is also associated with the thick cell coat of these cells.Recipient of a summer fellowship from the Kidney Foundation of Canada