Localization and regulation of angiotensin II receptors in renomedullary interstitial cells.
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Angiotensin Receptor Antagonists↗
Biomedical subjects
D Alcorn
Publications and source records attributed to D Alcorn.
Renin processing and secretion in adrenal and retina of transgenic (mREN-2)27 rats.
Two extrarenal tissue sources of renin were studied using quantitative assays and immunocytochemical methods during 12 hours following binephrectomy (BNx) in anesthetized hypertensive homozygous Ren-2 transgenic (TG) rats maintained off hypotensive drugs for three weeks. Compared to normal rats, circulating active renin was depressed 50% in conscious TG rats and prorenin was 5- to 10-fold higher. Post-BNx, arterial active and prorenin increased progressively to 10-fold, at which time adrenal venous outputs were 0.1 and 20 mGU/min, respectively. The ratio of active to prorenin (3.1 +/- 0.6%) remained unchanged with increasing plasma levels. Thus, either intrinsic enzyme activity of the transgenic prorenin contributed a constant proportion to the measured active renin, or processing to mature renin was coupled to prorenin synthesis and secretion in extrarenal tissues. In the TG rat eye, renin protein labeling was localized throughout retinal Müller cells with prosequence more obvious posteriorly, consistent with directional processing. Immunogold studies are in progress. In adrenal following BNx, labeling for renin and prosequence increased uniformaly in all zones of the cortex and in scattered medullary chromaffin cells. In cortex, both renin and prosequence were strongly located in intramitochondrial dense bodies. In chromaffin cells, renin labeling was present in both cytoplasmic vesicles and electron-dense granules, while prosequence was predominantly in cytoplasmic vesicles, consistent with processing of prorenin prior to storage in chromaffin granules.
Adrenal Glands↗
Effect of maternal glucocorticoid treatment on fetal fluids in sheep at 0.4 gestation.
Treatment of nine pregnant Merino ewes (64.0 +/- 0.4 days of gestation) with dexamethasone (D; 0.76 mg/h for 48 h) resulted in significant alterations in fetal fluids compared with eight saline-infused control animals (S; 63.0 +/- 0.9 days). There was a substantial increase in allantoic fluid volume (177 +/- 18 ml, D vs. 31 +/- 6, S) but no change in amniotic fluid volume (248 +/- 12 ml, D; 305 +/- 24, S). For allantoic fluid there was a significant decrease in osmolality (213 +/- 4 mosmol/kg water, D; 230 +/- 5, S) and alterations in composition. Amniotic fluid osmolality was unchanged (292 +/- 2 mosmol/kg water, D; 293 +/- 1, S), but amniotic fluid composition was affected. In four fetuses in which bladder and amniotic cannulas were inserted at gestational age 68-75 days, fetal urine flow rate increased from a mean of 4.1 +/- 1.1 to 13.8 +/- 2.6 ml/h after 24 h and 11.8 +/- 3.0 ml/h at 48 h for a similar maternal D infusion, whereas no such increase occurred in four control fetuses. All the fetal urine voided during a 3.5- to 4-h infusion of 51Cr-labeled EDTA into the fetal bladder was directed to the allantois. The results suggest that the increase in allantoic fluid volume resulted from increased fetal urine output into the allantoic compartment, although the composition of the excess allantoic fluid differed substantially from that of fetal urine. There was a greater incidence of abnormal cotyledons in the D-infused ewes.(ABSTRACT TRUNCATED AT 250 WORDS)
Allantoin↗
Cellular distribution of 125I-endothelin-1 binding in rat kidney following in vivo labeling.
Endothelin-1 (ET-1) receptors have previously been demonstrated in the rat kidney by in vitro autoradiography and in cultured renal cell lines by radioreceptor assay, but the precise cellular localization of these receptors under in vivo conditions remains to be determined. We performed electron microscopic autoradiography on rat kidney following intravenous administration of 125I-labeled ET-1. In vivo autoradiographs revealed binding patterns identical to those previously demonstrated following in vitro labeling. Light microscopic autoradiography showed that silver grains occurred exclusively overlaying glomeruli and peritubular capillaries in the cortex, inner stripe of the outer medulla, and the inner medulla. At the electron microscopic level, ET-1 binding was specifically localized to the fenestrated endothelium of glomerular and peritubular capillaries, and to a lesser extent to the vasa recta. No significant grains were seen on mesangial or visceral epithelial cells; nor were any seen on the cells of proximal tubule, the thick and thin limbs of the loop of Henle, the medullary collecting ducts, and renal interstitial cells. These results indicate that the endothelial cells of glomerular and peritubular capillaries are the primary target for the circulating ET-1 in the rat kidney and suggest an autocrine and/or paracrine function of locally synthesized ET-1 in vivo in both physiological and pathophysiological states.
Animals↗
In vivo occupancy of angiotensin II subtype 1 receptors in rat renal medullary interstitial cells.
Angiotensin II receptor binding sites in type 1 interstitial cells in the inner stripe of the outer medulla are readily labeled in vitro by the radioligand but not in vivo after systemic radioligand administration. In anesthetized rats, we investigated if reduced vascular delivery due to angiotensin II-induced renal vasoconstriction or, alternatively, prior occupancy of these sites by endogenous angiotensins modulates angiotensin II subtype 1 receptor binding to renal medullary interstitial cells in vivo using electron microscopic autoradiography. Using 125I-angiotensin II, administered systemically, as a radioligand, binding in control rats occurred predominantly in the glomeruli and proximal tubules, while only low binding was observed in the inner stripe of the outer medulla. Pretreatment of rats with unlabeled [Sar1,Ile8]angiotensin II or with the angiotensin II subtype 1 receptor antagonist losartan before receiving the radioligand completely abolished binding to all sites. Renal vasodilatation induced by sodium nitroprusside or use of the radiolabeled antagonist analogue 125I-[Sar1,Ile8]angiotensin II did not alter binding to the inner stripe. In contrast, chronic salt loading or inhibition of angiotensin-converting enzyme by perindopril significantly increased binding not only to the cortical sites but also to the sites in the inner stripe of the outer medulla. Electron microscopic autoradiographs of the inner stripe detected binding in the interstitial cells only in rats treated with chronic salt loading or perindopril. These results suggest that endogenous angiotensins may modulate binding of circulating angiotensin II to the interstitial cells in vivo, and these angiotensin II receptor-bearing cells are more likely to be more responsive to interstitial angiotensin II than to the circulating hormone.
1-Sarcosine-8-Isoleucine Angiotensin II↗
Renal and cardiovascular effects of renal medullary damage with bromoethylamine in dogs.
Bromoethylamine (BEA, 30-40 mg/kg) was administered to dogs to determine whether damage to the inner medulla of the kidney, the putative source of a depressor hormone, causes hypertension in this species. Bromoethylamine produces hypertension in rats but this has not been confirmed in other species, although we have shown that this dose of BEA in dogs abolishes the release of a reno-medullary vasodepressor hormone in response to marked increases in renal perfusion pressure. During acute BEA administration over 1 h to conscious dogs, there were no significant effects on renal blood flow, arterial pressure or total peripheral resistance, but there was a significantly greater diuresis compared to vehicle administration. Over the first 10-14 days after BEA, daily urine output rose 5-10 fold initially and plasma creatinine concentration rose markedly. There was no significant effect on arterial pressure, cardiac output, total peripheral resistance, or renal blood flow over this period. BEA administration caused extensive damage to the thin limbs of the loops of Henle, widespread thrombosis of blood vessels and haemorrhage into the interstitium of the dog renal medulla. Reno-medullary interstitial cells were devoid of lipid droplets, were synthetic, and were associated with increased amounts of extracellular matrix. Thus extensive renal medullary damage by BEA administration to conscious dogs did not alter resting systemic haemodynamics, and these results therefore provide no evidence for a role for the medulla in the maintenance of resting arterial pressure in the dog.
Animals↗
Effects of angiotensin converting enzyme inhibition on glomerular number, juxtaglomerular cell activity and renin content in experimental unilateral hydronephrosis.
OBJECTIVE: To determine the effects of hydronephrosis on glomerular number and juxtaglomerular cell synthetic activity and the protective influence of angiotensin converting enzyme inhibition. DESIGN: A comparison of sham and contralateral kidneys with 8-week ipsilateral ureteral ligated hydronephrotic kidneys in BALB/c mice. Enalapril was administered from 5 weeks in additional sham and hydronephrotic kidney groups. METHODS: Renin and prorenin immunohistochemistry was applied to sections of perfusion-fixed kidneys at the light and electron microscope level. Glomerular number was estimated by a physical disector-fractionator stereological method. An enzyme kinetic renin assay was performed in kidney tissue and plasma. RESULTS: Glomerular number in hydronephrotic kidneys decreased significantly compared with sham and contralateral kidneys. Renin content in hydronephrotic kidneys did not change compared with sham or contralateral kidneys, but the renin content in the glomerulus was significantly greater in hydronephrotic than in contralateral kidneys and similar to in sham kidneys. Contralateral kidneys enlarged significantly and their total renin content decreased significantly compared with hydronephrotic and sham kidneys. Plasma renin was unchanged. Fewer juxtaglomerular cells were labelled for renin and prorenin in contralateral than in hydronephrotic or sham kidneys. Granulopoiesis and exocytotic profiles were markedly greater in hydronephrotic than in contralateral or sham kidneys. Following enalapril, glomerular number was significantly higher in hydronephrotic kidneys and renin content increased proportionally more in contralateral than in hydronephrotic or sham kidneys. CONCLUSION: Hydronephrosis for 8 weeks results in atrophy of 50% of glomeruli and exerts an inhibitory influence on contralateral juxtaglomerular cells while augmenting ipsilateral renin production per remaining glomerulus with maintenance of plasma renin. Enalapril preserves glomeruli and reverses the contralateral inhibitory influence, suggesting an angiotensin-related mechanism.
Angiotensin-Converting Enzyme Inhibitors↗
Scanning and transmission electron-microscopic study of peripolar cells in the newborn lamb kidney.
Scanning and transmission electron microscopy were used to study the ultrastructural characteristics and positions of granulated peripolar cells in newborn lamb kidney. Following tissue fixation by vascular perfusion in situ, the vascular pole region of the glomerulus was exposed for examination by scanning electron microscopy following removal of the glomerular tuft. Peripolar cells were recognized by their surface morphology enabling their quantification and an assessment of the relationship of their position in the renal cortex. The prominent expression of peripolar cells in this species was confirmed. Almost every vascular pole examined revealed peripolar cells (405 out of 407; 99.5%) and thus, throughout the cortex, the distribution of peripolar cells was the same as the distribution of renal corpuscles. Larger, more protruding peripolar cells were observed in the outer cortical renal corpuscles. The numbers of peripolar cells encircling each vascular pole ranged from 1 to 10. There was no correlation between number of granulated peripolar cells at the vascular pole and the position of the renal corpuscle within the renal cortex. As viewed by transmission electron microscopy, organelles of protein synthesis were abundant in the cytoplasm of peripolar cells. Exocytosis of cytoplasmic granules was observed by both scanning and transmission electron microscopy implying that a process of regulative secretion occurs from these cells. The use of ultrastructural techniques has provided evidence supporting the concept that peripolar cells are prominent in the cuff region of each renal corpuscle of the newborn lamb and furthermore that peripolar cells in this species most likely have a secretory function.
Animals↗
Renin processing in cultured juxtaglomerular cells of the hydronephrotic mouse kidney.
We examined renin processing in cultured juxtaglomerular (JG) cells of the hydronephrotic mouse kidney with immunocytochemical and biochemical techniques. Compared with JG cells in normal kidneys, there was less intense labeling for renin protein in mature granules of cultured JG cells. However, pro-renin labeling of transport vesicles and juvenile granules was maintained, suggesting incomplete passage of pro-renin through intermediate and mature granules. Immunogold evidence of exocytosis of mature granules containing renin protein was present at all stages. Labeling of transport vesicles for pro-renin, together with the absence of exocytosis of pro-renin from juvenile granules, indicated that pro-renin was exclusively released by a constitutive process. Active renin release into supernatants decreased with time, whereas the ratio of total renin to active renin increased, indicating that pro-renin synthesis and release were maintained but that the processing of pro-renin to active renin was interrupted. Angiotensin II inhibited and verapamil stimulated active renin release in culture; neither substance affected pro-renin release. Application of secretagogues that act via intracellular calcium or cAMP resulted in depletion of mature granules and their deformation by myelin figures and vacuoles, findings consistent with an exocytosis from mature granules. The absence of effect of any secretagogues on pro-renin release suggests that these stimulatory mechanisms are exclusively post-Golgi. In cultured JG cells in renal explants, renin vesicular transport and granular exocytosis are maintained but a defect in pro-renin passage from juvenile to intermediate granules is apparent.
Angiotensin II↗
Thyroxine transport to the brain: role of protein synthesis by the choroid plexus.
A cell culture model for the blood-cerebrospinal fluid barrier in choroid plexus was developed. The relationship between synthesis and secretion of transthyretin across a layer of epithelial cells derived from rat choroid plexus and the transport of T4 was analyzed in a two-chamber system. Choroid plexus cells were dispersed and placed on a porous filter suspended in cell culture medium. A monolayer of polarized epithelial cells developed after 5 days in culture, separating fluid in the upper (apical) chamber from fluid in the lower (basal) chamber. Electrical resistance across the cell layer was 100 Ohm/cm2. Transthyretin was synthesized and secreted by these cells. Over 32 h, transthyretin accumulated in the fluid in the apical chamber to twice the concentration in the basal chamber. [125I]T4 added to the basal chamber permeated to the apical fluid and accumulated in the apical chamber to twice the concentration in the basal fluid. Upon inhibition of protein synthesis, T4 equilibrated to a similar concentration in the two chambers. Thus, the accumulation of T4 in the apical chamber required continuing protein synthesis. Competitive inhibition of T4 binding to transthyretin by EMD 21388 also prevented the accumulation of T4 to a higher concentration in the upper than in the lower chamber. These data suggest that T4 partitions through the choroid plexus and that transthyretin synthesis and secretion by the choroid plexus determines the concentration of T4 in the apical fluid. A model is proposed for the involvement of transthyretin secreted by the choroid plexus, in the in vivo distribution of T4 in the brain.
Animals↗
The glomerular peripolar cell.
The PPC is a distinctive granulated epithelial cell at the vascular pole of the glomerulus. It is present in a wide range of animal species. It is especially prominent in sheep, particularly the newborn lamb. To date, it has been shown that its granules contain albumin, immunoglobulins, neuron-specific enolase and transthyretin. It does not appear to contain renin. The function of the PPC awaits clarification. It has been postulated that it may play a role in the synthesis and secretion of factors involved in modulating renal tubular function.
Animals↗
Localization and properties of angiotensin II receptors in rat kidney.
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Animals↗
Immunohistochemical localization of transthyretin in glomerular peripolar cells of newborn sheep.
Purified transthyretin has been isolated from sheep serum. Antiserum raised against this protein has been used with an indirect immunoperoxidase histochemical technique to identify transthyretin in newborn lamb kidney tissue. Transthyretin was found in proximal tubule cells and in glomerular peripolar cells. Preabsorption studies using purified transthyretin protein indicate that the immunoreactivity of the antiserum is specific to transthyretin.
Animals↗
Renin processing studied by immunogold localization of prorenin and renin in granular juxtaglomerular cells in mice treated with enalapril.
Immunogold techniques were used to investigate renin processing within granular juxtaglomerular cells following short-term (6 h and 1 day) and long-term (4 weeks) enalapril treatment in female BALB/c mice. In control animals, renin protein labelling was localized to all types of granules (proto-, polymorphous, intermediate and mature) and to transport vesicles, whilst prorenin labelling was found in all these sites except mature granules, confirming that active renin is localized to mature granules only. Following short-term enalapril treatment, the exocytosis of renin protein from mature granules was increased. Long-term enalapril treatment resulted in increased numbers of transport vesicles and all types of granules, consistent with increased synthesis and storage of renin. More large intermediate granules contained discrete regions labelled for prorenin. Renin protein was exocytosed from individual and multiple granules, whilst prorenin was exocytosed from proto- and intermediate granules. It is concluded that under normal conditions prorenin is secreted constitutively by bulk flow from transport vesicles. On the other hand, active renin is secreted regulatively from mature granules. In conditions of intense stimulation (angiotensin-converting enzyme inhibition treatment), increased synthesis of prorenin leads to enhanced secretion of prorenin by both constitutive and regulative pathways. Under these conditions, the conversion of prorenin to active renin is increased, with increased secretion of active renin occurring in a regulative manner. Furthermore, the localization of prorenin to one discrete region of large intermediate granules leads us to conclude, that cleavage of the prosegment of renin occurs with the transition of intermediate to mature granules.
Animals↗
High resolution localization of angiotensin II receptors in rat renal medulla.
The cellular localization of angiotensin II (Ang II) receptors in the inner stripe of the outer medulla of the rat kidney was investigated by using high resolution light and electron microscopic autoradiography. Fresh tissue blocks from the inner stripe of the outer medulla were incubated with 125I-[Sar1, Ile8] Ang II and prepared for microscopic autoradiography. At the light microscopic level, 125I-[Sar1, Ile8] Ang II was found to penetrate into the tissue and to bind specifically to sites outlining renal tubules and vasa recta bundles. Electron microscopic autoradiography revealed that silver grains were detected over interstitial cells located between the tubules and components of the vasa recta bundles, but no silver grains were detected overlying the cells of the thin descending or thick ascending limbs of the loop of Henle, the collecting ducts, the vasa recta, or other blood vessels. These interstitial cells contained abundant endoplasmic reticulum, microfilaments, occasional lipid droplets and extensive cytoplasmic processes which closely related to the basement membranes of the vasa recta and loops of Henle. The cells therefore closely resemble type 1 interstitial cells. Since Ang II binding sites are absent in the inner medulla, the cells labelled by this technique must be a subset of type 1 interstitial cells, distinct from the typical lipid-laden interstitial cells most abundant in the inner medulla. These findings demonstrate that type 1 interstitial cells are the primary sites for a high density of Ang II receptors located in the inner stripe of the outer medulla.
Animals↗
Morphometric analysis of the actions of angiotensin II on renal arterioles and glomeruli.
To study the effects of angiotensin II on afferent and efferent arteriole diameters and on intraglomerular dimensions, angiotensin II (20 ng.kg-1.min-1) or saline vehicle was infused intravenously for 20 min into anesthetized rabbits pretreated with enalapril. Both kidneys were perfusion fixed (glutaraldehyde), and vascular casts were made of the right kidneys using methacrylate. Morphometric analysis of the left kidneys using transmission electron microscopy revealed no significant effects of angiotensin II within the glomerulus, including the degree of mesangial contraction. The diameters of the afferent and efferent arteriole casts from the right kidneys were measured at 20, 50, and 75 microns from the glomerulus by scanning electron microscopy. In the outer cortex the mean diameters of the afferent and efferent arterioles were 14.1 +/- 0.8 and 9.7 +/- 0.5 microns, respectively, in the angiotensin II-infused rabbits, significantly less than in the control (vehicle) rabbits, 17.0 +/- 0.7 microns (P less than 0.001) and 10.7 +/- 0.4 microns (P less than 0.005), respectively. Calculation of the relative changes in vascular resistance, however, indicated that the effects of angiotensin II on efferent arteriole resistance (average difference 2.4 +/- 1.2 units/microns) were significantly greater per unit length than the effects on afferent arteriole resistance (average difference 0.9 +/- 0.3 units/microns). Thus infused angiotensin II caused greater reduction in afferent arteriolar diameter than in efferent, but the calculated increase in vascular resistance per micron was greater in efferent vessels due to their smaller resting diameter.
Angiotensin II↗
Diagnostic criteria: tuberous sclerosis complex. Report of the Diagnostic Criteria Committee of the National Tuberous Sclerosis Association.
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Child↗
The role of the macula densa in renin synthesis.
1. The role of the macula densa in renin synthesis was studied using mice with one hydronephrotic kidney. 2. Renin synthesis was assessed by measurement of renal renin, renal mRNA for renin and plasma renin. 3. Sodium depletion stimulated mRNA and renal renin to a similar extent in the hydronephrotic and contralateral kidney. 4. Enalapril stimulated mRNA concentration in both kidneys but renal renin did not rise in the hydronephrotic kidney. 5. Propranolol did not alter the response to sodium depletion in either kidney. 6. The macula densa is not crucial for the stimulation of renin synthesis following sodium depletion. However, it may regulate renin production after mRNA synthesis, possibly by controlling the conversion of prorenin to renin.
Animals↗