Protein increases glomerular eicosanoid production and activity of related enzymes.

We examined the in vitro production of PGE2, 6-keto PGF1 alpha and TxB2 by isolated glomeruli from rats fed a low (6% casein) or a high (40% casein) protein diet for approximately eight weeks. Glomeruli from high protein-fed rats produced significantly greater amounts of PGE2, 6-keto PGF1 alpha and TxB2 under basal conditions and in response to the addition of 100 nM angiotensin II (Ang II) than glomeruli from low protein-fed rats. To elucidate the mechanisms by which greater protein intake enhanced the glomerular production of eicosanoids, we explored phospholipase (A2 and C) and cyclooxygenase activity in glomeruli isolated from low- or high-protein fed rats. PE-specific PLA2 activities were significantly increased in glomeruli from rats fed a high protein diet when compared to a low protein diet. On the other hand, PC-specific PLA2 activities were significantly decreased in glomeruli from rats fed a high protein diet. No significant difference in PIP2-PLC activities was detected between glomeruli of the two dietary groups. The cyclooxygenase content and activity was significantly greater in glomeruli from rats fed a high protein diet than in glomeruli from rats fed a low protein diet. Glomeruli of rats fed a 50/50 mixture of the diets (23% casein) had amounts and activity of cyclooxygenase and activities of PE-specific PLA2 intermediate between those of high and low protein-fed animals. In conclusion, increased synthesis of eicosanoids by glomeruli from rats fed a high protein diet may be mediated by increases in the amount and activity of cyclooxygenase coupled with enhanced activity of PE-specific PLA2.     

Eicosanoid production by isolated glomeruli of rats with unilateral ureteral obstruction

The production of PGE2 6-keto PGF1 alpha and TxB2 under basal conditions and after exposure to angiotensin II was examined in vitro in isolated glomeruli from sham-operated control rats and rats with unilateral ureteral obstruction of 24 hour duration, that were or were not pretreated with an inhibitor of the angiotensin I converting enzyme (ACE). Basal prostanoid production was greater in glomeruli from the obstructed kidney (OK) than in glomeruli from the contralateral kidney (CLK) of rats with obstruction or glomeruli from the kidneys of sham-operated rats. Glomeruli obtained from the CLK of rats with unilateral obstruction also produced more PGE2 and 6-keto PGF1 alpha than glomeruli obtained from kidneys of sham-operated rats. Administration of an ACE inhibitor to rats with unilateral obstruction in vivo returned basal prostanoid production in vitro to levels seen in glomeruli of sham-operated rats. The increase in prostanoid production in response to angiotensin II added in vitro was less in glomeruli from rats with unilateral obstruction than in glomeruli from sham-operated rats. However, the response was restored to that seen in glomeruli of sham-operated rats after blockade of angiotensin II synthesis in vivo in rats with unilateral obstruction. Blockade of angiotensin II synthesis in sham-operated rats did not affect prostanoid synthesis by their glomeruli.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glomerular prostaglandin production in diabetic rats with renovascular hypertension

A rat model combining two-kidney, one-clip (2K1C) renovascular hypertension and streptozotocin-induced diabetes mellitus was used to assess the pathogenetic significance of vasodilator prostaglandins in diabetic glomerular injury. Glomeruli isolated from normotensive diabetic rats produced greater than normal amounts of PGE2 and 6-keto PGF1 alpha under in vitro incubation conditions. In 2K1C hypertensive-diabetic rats, glomeruli from unclipped kidneys (which are prone to accelerated diabetic glomerular injury) produced similarly elevated amounts of PGE2 and 6-keto PGF1 alpha, which significantly exceeded the levels produced by glomeruli from clipped kidneys (which are relatively protected from glomerular injury), despite exposure to a similar diabetic environment. In contrast, glomeruli from both unclipped and clipped kidneys of 2K1C hypertensive-non-diabetic rats produced normal amounts of PGE2 and 6-keto PGF1 alpha. These results suggests a correlation between vasodilator prostaglandin metabolism and susceptibility to diabetic glomerular injury, and illustrate that enhanced glomerular prostaglandin production is not an invariable metabolic consequence of hyperglycemia or insulin deficiency. The data also demonstrate that hemodynamic as well as metabolic factors may influence glomerular prostaglandin metabolism in experimental diabetes mellitus.     

The effect of cyclosporine on agonist-stimulated glomerular and mesangial cell vasodilatory prostaglandin production

Cyclosporine A administration produces an increase in renal vascular resistance and a decrease in glomerular filtration rate in both human and animal models. CsA usage in humans has also been shown to alter the ability of the kidney to adapt to alterations in renal hemodynamics. CsA alters the production of prostaglandins by isolated rat glomeruli. Normally, vasoconstrictive agents stimulate the production of vasodilatory glomerular and mesangial cell PG. To determine if CsA alters glomerular and mesangial cell (MC) vasodilatory PG production in response to vasoconstrictive agents, we administered CsA, 20 mg/kg, or vehicle to rats for 7 days, or incubated mesangial cells with CsA 1 mcg/ml for 24 hr. Ex vivo glomerular PGE2 and 6-keto-PGF1a production was determined in the presence or absence of angiotensin II 10(-6) M and norepinephrine 10(-5)M. CsA administration decreased glomerular production of both eicosanoids in the basal and stimulated state. Incubation of MC with CsA markedly suppressed PGE2 and 6-keto-PGF1a production in response to stimulation with 200 nM angiotensin II. To determine if CsA inhibits angiotensin II-stimulated PG production prior to protein kinase C, we incubated glomeruli and MC with the diacylglycerol mimetic OAG. CsA depressed OAG-stimulated glomerular and MC PGE2 and 6-keto-PGF1a production. Conversely, CsA stimulated the production of PGE2 by renal medullary slices. We conclude that CsA blunts the vasoconstrictor-induced increase in glomerular and mesangial cell vasodilatory PG production, thereby removing a compensatory mechanism that maintains GFR in states of vasoconstrictor excess.     

Renal functional reserve in the early stage of experimental diabetes.

The role of renal functional reserve (RFR; increase in plasma flow and glomerular filtration rate in response to protein loading) as an indicator of increased glomerular hydrostatic pressure and flow was evaluated in recent-onset poorly controlled diabetic rats. Streptozocin-induced diabetic (STZ-D) rats were studied with micropuncture (MP) technique after 10-15 days of diabetes (daily blood glucose level 15.3-18 mmol). We also studied STZ-D rats treated with the converting-enzyme inhibitor (CEI) enalapril or the angiotensin II (ANG II) receptor antagonist DuP 753 (DuP) for 3 days before MP. Nondiabetic rats (NOR) served as controls. Glomerular hemodynamics and proximal tubular reabsorption were measured in the control period and during intravenous glycine infusion. In NOR rats, glycine increased single-nephron plasma flow (SNPF) and single-nephron glomerular filtration rate (SNGFR). Although STZ-D rats did not exhibit hyperfiltration, SNGFR and SNPF were not modified by glycine, defining loss of RFR. CEI rats responded to glycine with an increase in SNGFR due to a rise in SNPF and a rise in the ultrafiltration coefficient. Interestingly, loss of RFR in STZ-D rats was associated with a decrease in absolute proximal reabsorption. The decrease in absolute proximal reabsorption was corrected by both CEI and DuP, although glomerular vasodilation was restored only in the CEI group. In conclusion, at the early stage of diabetes mellitus, loss of RFR does not detect hyperfiltration, but rather the presence of a tubular alteration probably dependent on ANG II.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prostaglandin and thromboxane synthesis by rat glomerular epithelial cells

Isolated rat glomeruli have been shown to synthesize prostaglandin (PG) and thromboxane (Tx). In this study, we evaluated, by radioimmunoassay and radiochromatographic methods, PG and Tx synthesis by glomerular cells in culture. Transmission and scanning electron microscopy showed polygonal cells, attached by desmosomes, with surface microvilli. These features are typical of glomerular epithelial cells. Incubation of these glomerular epithelial cells with arachidonic acid (C20:4) resulted in an array of endproducts with concentrations of PGE2 greater than TxB2 greater than PGF2 alpha greater than 6-keto-PGF1 alpha . Addition of angiotensin II (AII) to the cultured glomerular cell produced almost exclusive stimulation of PGE2 with PGE2 much much greater than PGF2 alpha greater than TxB2 = 6-keto-PGF1 alpha . AII and AIII (100 micrometer to 1 micrometer ) stimulated PGE2 in glomerular epithelial cells, and the increments of PGE2, as a function of the concentration of AII or AIII, were similar. The sar1-thr8-AII analog inhibited both AII- and AIII-stimulated PGE2 synthesis. The divalent cation ionophore A23187 in concentrations of 0.2 to 2.0 micrometer increased primarily PGE2 and TxB2 synthesis with smaller increases of PGF2 alpha and 6-keto-PGF1 alpha . The relative concentrations of PG and Tx produced by rat glomerular epithelial cells, incubated with C20:4 or A23187, were similar. Our results demonstrate that: (1) the predominant cell grown in culture from the rat glomerulus, after 9 days, is the epithelial cell; (2) this cell is capable of PG and Tx synthesis; (3) stimulation of PG by AII and AIII may be mediated by the same cellular receptor, AII and AIII increase primarily the synthesis of a vasodilatory PG, PGE2; (4) exogenous substrate C20:4 or release of endogenous C20:4 by the divalent cation ionophore A23187 not only stimulates PGE2 but also the vasoconstrictor TxA2; and (5) the PG and Tx endproducts synthesized by epithelial cells may be determined by an intracellular coupling of the specific synthetic enzymes with different pools of C20:4.     

Urinary excretion and glomerular synthesis of prostaglandin E2 and prostaglandin F2 alpha in cirrhotic, non-ascitic rats: the effects of sodium overload

The urinary excretion of aldosterone, kallikrein and prostaglandin E2 (PGE2) was studied in sodium-retaining (RC) and nonretaining (NRC), nonascitic cirrhotic rats, under basal conditions and after an oral sodium load (5 mmol). The glomerular synthesis of PGE2 was measured in RC rats under the same conditions. Both groups of cirrhotic animals showed a decreased urinary excretion of PGE2. Isolated glomeruli of RC rats produced less PGE2 than those of the control animals, both under basal conditions and after the sodium load. The NRC group was the only one able to increase the urinary excretion of kallikrein in response to the sodium load. These findings could contribute to explain the early physiopathological events of hepatic cirrhosis.     

Up-regulation of glomerular COX-2 by angiotensin II: role of reactive oxygen species

BACKGROUND: Prostaglandins such as prostaglandin E(2) (PGE(2)) and prostaglandin I(2) (PGI(2)) counteract the angiotensin II (Ang II)-induced vasoconstriction in the glomerular microcirculation. We have shown that Ang II promotes mesangial cell hypertrophy via reactive oxygen species (ROS), which originate from nicotinamide adenine dinucleotide phosphate and its reduced form (NADH/NADPH) oxidase. It has been reported that conditions associated with activation of the renin-angiotensin system result in increased glomerular cyclooxygenase-2 (COX-2) expression and activity. METHODS: We designed studies to determine (1) whether Ang II induces COX-2 in the glomerulus in vivo in the glomerulus as well as in vitro in mesangial cells, (2) whether ROS originated from Ang II are involved, and (3) whether COX-2-derived prostaglandins modulate the growth promoting effects of Ang II in mesangial cells. Rats were infused with Ang II (0.7 mg/kg/day) for 5 days and glomerular COX-2 expression and activity assessed in isolated glomeruli. RESULTS: Ang II increased glomerular PGE(2) production (100%) accompanied by a concomitant increase in glomerular COX-2 expression at the mRNA (1.7-fold) and protein level (sixfold). In mesangial cells, Ang II significantly increased mesangial cell PGE(2) (200%) and PGI(2) (100%) production as well as COX-2 mRNA that was prevented by the angiotensin type 1 (AT1) receptor blocker irbesartan and the COX-2 inhibitor NS-398. The NADPH oxidase inhibitor diphenyleneiodonium (DPI), the ROS scavenger tiron as well as catalase, inhibited Ang II-induced PGE(2) production suggesting that Ang II-induced ROS mediate COX-2 up-regulation. Strikingly, COX-2 inhibition as well as blockade of the type 1 PGE(2) receptor (EP1) prevented Ang II-induced mesangial cell hypertrophy suggesting that COX-2-derived prostaglandins, and specifically PGE(2), importantly contribute to the growth promoting effects of Ang II. CONCLUSION: These studies suggest that blockade of specific PGE(2) receptors may be a novel strategy to modulate the pathologic effects of COX-2-derived prostaglandins without simultaneously affecting protective vasodilatory mechanisms.     

Decreased glomerular proteinase activity in the streptozotocin diabetic rat.

Decreased glomerular proteinase activity may contribute to matrix accumulation in diabetes. Male Sprague-Dawley rats were rendered diabetic by injection of streptozotocin (STZ) 65 mg/kg i.v.; age-matched, sham-injected rats served as controls. Glomeruli from diabetic rats 1 month after STZ injection demonstrated significant decreases in collagenase and cathepsin B activities compared to control glomeruli. Treatment with insulin resulted in a slight (but not significant) increase in collagenase activity and normalized cathepsin B activity. We conclude that decreased glomerular collagenase and cathepsin B activities are present in STZ diabetes. These alterations may contribute to mesangial matrix accumulation.     

Mechanism of the decreased eicosanoid production in vitro in response to angiotensin II in glomeruli of rats with bilateral ureteral obstruction

Summary: Glomeruli isolated from rats with bilateral ureteral obstruction (BUO) of 24 h duration synthesized significantly greater amounts of prostaglandin (PG)E₂, 6-keto PGF_1a, thromboxane (Tx)B₂ and leukotriene (LT)B₄ than glomeruli isolated from sham-operated control (SOC) rats. Glomeruli isolated from SOC rats produced increased amounts of these four eicosanoids compared to basal conditions when 100 nmol/L angiotensin II (AII) was added in vitro to the preparations. However, no significant increases in glomerular eicosanoid production were seen under these conditions in glomeruli of rats with BUO. to examine the mechanims underlying imparied eicosanoid production in glomeruli of rats with BUO exposed to AII in vitro, we measured the activities of phosphatidylethanolamine (PE)-specific phospholipase A₂ (PLA₂), 5-lipoxygenase and the cyclo-oxygenase pathway enzymes including cyclo-oxygenase, PGE₂ isomerase and PGI₂ and Tx synthases under basal conditions and after addition of 100 nmol/L AII in vitro in glomeruli isolated from SOC rats and rats with BUO of 24 h duration. the basal activities of all of these enzymes were significantly greater in glomeruli of rats with BUO compared to SOC rats. In glomeruli of SOC rats, the activities of these enzymes were markedly increased when exposed to 100 nmol/L AII in vitro compared to basal conditions. By contrast, no significant changes in the activities of enzymes involved in eicosanoid formation above baseline were seen in glomeruli of rats with BUO exposed to AII in vitro. the production rates of eicosanoids paralleled the activities of these enzymes under basal and AII-stimulated conditions in glomeruli obtained from SOC rats and rats with BUO. Thus, the lack of increased levels of PGE₂, 6-keto PGF_1a, TxB₂ and LTB₄, when glomeruli of rats with BUO of 24 h duration are exposed to 100 nmol/L AII in vitro, maybe due mainly to either the action of PE-specific PLA₂ or the combined action of PE-specific PLA₂, cyclo-oxygenase pathway enzymes and 5-lipoxygenase set at, or near, maximum levels as a consequence of BUO.     

Effects of polyol-pathway inhibition and dietary myo-inositol on glomerular hemodynamic function in experimental diabetes mellitus in rats

Early functional disturbances in nerve, retina, and lens in diabetes mellitus appear to result from a common mechanism involving increased polyol-pathway activity with an associated effect on tissue myo-inositol metabolism. We tested the role of increased polyol-pathway activity in the early glomerular hemodynamic abnormalities in experimental diabetes in rats with dietary myo-inositol supplementation or the administration of sorbinil, an aldose reductase inhibitor. Each maneuver prevented the glomerular hyperfiltration of early streptozocin-induced diabetes and reversed the hyperfiltration of established diabetes of 10 days' duration. We also found that the abnormal response to captopril in diabetic rats was improved by dietary myo-inositol supplementation or sorbinil administration. Although nonhypotensive doses of captopril lowered glomerular filtration rate (GFR) in diabetic rats on a 0.01% myo-inositol diet, GFR increased substantially after captopril infusion in diabetic rats treated with sorbinil or myo-inositol supplementation. These data suggest that normalization of tissue myo-inositol metabolism restores normal responsiveness to angiotensin II; this may contribute to the reduction in GFR with the two experimental maneuvers. We also tested the interaction between polyol-pathway activation and high dietary protein intake. Aldose reductase inhibition and dietary myo-inositol supplementation had no effect on the component of increased GFR due to 50% dietary protein intake but specifically inhibited the hyperfiltration attributable to diabetes. These results suggest that hyperglycemia acts through increased polyol-pathway activity and its effects on tissue myo-inositol metabolism to play a fundamental role in the pathogenesis of the glomerular hyperfiltration characteristic of early diabetes.     

Angiotensin II stimulation of prostaglandin E2 and 6-keto-F1 alpha formation by isolated human glomeruli

The intrinsic in vitro production of prostaglandins (PGs) E2, F2 alpha, 6-keto-F1 alpha, and thromboxane B2 (TxB2) and the conversion of exogenous substrate to PGs and TxB2 by isolated human glomeruli was demonstrated, 6-keto-PGF1 alpha was the major product. This was observed under basal conditions and following incubation with exogenous substrate. Indomethacin (Indo; 10(-4 M) inhibited the conversion of arachidonic acid to PGs and the release of [1-14C]-labeled products from human glomeruli by about 80%. The addition of angiotensin II (AII) to the isolated glomeruli produced, under basal conditions, an almost selective stimulation of 6-keto-PGF1 alpha. Following the prelabeling of glomeruli with 1-14C-arachidonic acid, the increase of glomerular PG formation after AII was added was also only significant for 6-keto-PGF1 alpha. When glomeruli were preincubated with large amounts of non-radiolabeled substrate. AII stimulated PGE2 and 6-keto-PGF1 alpha formation significantly. The data demonstrate PG formation in isolated human glomeruli and show an interaction between AII and the prostaglandin system in this tissue. This interrelationship might have physiologic consequences in the regulation of glomerular hemodynamics.     

Fosinopril ameliorates exogenous cholesterol-induced incipient glomerular lesions in obese Zucker rats. Effects on eicosanoid secretion

Background: To date, the role of dietary cholesterol as a risk factor for some diabetic nephropathy, such as mesangial expansion and glomerular lesions, is unknown. Controversy also exists regarding the effects of prostaglandin-induced changes in glomerular haemodynamics on the appearance of glomerulo-sclerosis. Methods: We have used obese Zucker rats (OZRs) as a model of early nephropathy to evaluate the effect of hypercholesterolaemic diet on glomerular prostaglandin secretion and on the development of glomerular lesions. Due to the role of angiotensin II (Ang II) in glomerular haemaodynamics, we have also evaluated its effects on glomerular eicosanoid secretion. Furthermore, as it has been suggested recently by clinical studies that angiotensin-converting enzyme inhibitors (ACEIs) reduce serum lipids associated with proteinuria, we have also evaluated the effect of the ACEI, fosinopril, both in vivo and in vitro, using 24 h glomeruli cultures. Results: Results showed that a cholesterol-rich diet significantly increased serum cholesterol, proteinuria and glomerular eicosanoid secretion, and caused macrophage-ED1 cell deposits in the glomerular mesangium. Segmentary lesions only appeared in those rats with the highest percentage of glomerular xanthomatous (macrophage-ED1) cells. Ang II, per se, caused a marked rise in glomerular prostaglandin E2 and thromboxane B2. The inhibition of Ang II synthesis with fosinopril reduced all the parameters listed above whereas Ang II (10^-6 M) increased the secretion of TxB2 and tended to increase PGE2 secretion in glomerular culture. Conclusions: In conclusion, exogenous cholesterol per se may contribute to nephropathy by increasing eicosanoid secretion, serum lipid profile, urinary protein excretion and the development of glomerular lesions. Fosinopril reduced all these parameters probably by its effects on Ang II. Key words: angiotensin-converting enzyme inhibitors; angiotensin II; eicosanoid secretion; incipient glomerular lesion; macrophage-ED1 cells; nephropathy; xanthomatous cells      

Mesangial function and glomerular sclerosis in rats after unilateral nephrectomy

To investigate the possible relationship between disturbance of mesangial function and segmental localization of glomerular sclerosis, five uninephrectomized male Wistar rats and five sham-operated controls received colloidal carbon intravenously. At 4 months 8.4 +/- 2.5% of the glomeruli of the nephrectomized rats showed focal sclerosis. Glomeruli of nephrectomized rats contained significantly more carbon than glomeruli of controls. Glomeruli with focal sclerosis contained significantly more carbon than normal glomeruli in the same kidneys with a preferential tracer localization within the lesions. In another experiment carbon injections were given before surgery. At 4 months 12.6 +/- 4.1% of the glomeruli of the nephrectomized rats showed focal sclerosis, an incidence not significantly different from that of the first experiment. Glomerular carbon content was equal in experimental and control rats and no preferential localization of the tracer within the lesions was found. From these results we conclude that the preferential localization of carbon in the glomerular lesions in rats nephrectomized before injection of carbon is caused by the increased delivery of tracer shortly after injection to those glomerular areas where sclerosis will develop at a later time. The development of focal sclerosis may be related to the local deposition of harmful substances from the circulation.     

Mesangial function and glomerular sclerosis in rats with aminonucleoside nephrosis

The possible relationship between mesangial dysfunction and development of glomerular sclerosis was studied in the puromycin aminonucleoside (PAN) model. Five male Wistar rats received repeated subcutaneous PAN injections; five controls received saline only. After 4 weeks the PAN rats were severely proteinuric (190 +/- 80 mg/24 hr), and all rats were given colloidal carbon (CC) intravenously. At 5 months glomerular sclerosis was found in 7.6 +/- 3.4% of the glomeruli of PAN rats; glomeruli of the controls were normal. Glomeruli of PAN rats contained significantly more CC than glomeruli of controls. Glomeruli with sclerosis contained significantly more CC than non-sclerotic glomeruli in the same kidneys. CC was preferentially localized within the sclerotic areas of the affected glomeruli. Since mesangial CC clearance from the mesangium did not change during chronic PAN treatment, we conclude that this preferential CC localization within the lesions is caused by an increased CC uptake shortly after injection in apparent vulnerable areas where sclerosis will develop subsequently. Cluster analysis showed a random distribution of lesions in the PAN glomeruli in concordance with the random localization of mesangial areas with dysfunction in this model. Similar to the remnant kidney model in PAN nephrosis the development of glomerular sclerosis may be related to "mesangial overloading."     

Aldose reductase inhibition and glomerular abnormalities in diabetic rats

We examined the effects of aldose reductase inhibition (ARI) on glomerular filtration rate (GFR), albuminuria, and kidney histology in partially insulin-treated streptozocin-induced diabetic (STZ-D) rats. After 1 mo of diabetes, GFR was elevated over control values in the STZ-D rats but was not affected by treatment with statil (an aldose reductase inhibitor). In another set of rats maintained for 7 mo, albuminuria was significantly increased in the diabetic rats from 2 mo on but was also not affected by statil treatment. Similarly, histological glomerular damage and diabetes-induced kidney hypertrophy were also greater in diabetic animals but were not altered by statil treatment. The frequency of diabetic cataracts was reduced by statil, and erythrocyte and kidney sorbitol levels were normalized, confirming the efficacy of ARI. Thus, inhibition of the aldose reductase pathway with statil does not ameliorate the hemodynamic, proteinuric, histological, or growth abnormalities in this model of diabetic nephropathy.     

Do glomerular hemodynamic adaptations influence the progression of human renal disease?

Although experiments in the rat suggest that glomerular hemodynamic alterations following a reduction of renal mass may be implicated in the progression of chronic renal failure, we argue that the deleterious effects of similar adaptations in human renal disease are unproven. In the otherwise normal solitary kidney the supranormal glomerular filtration rate (GFR) remains stable over the longterm, and in early diabetic nephropathy which is also accompanied by hyperfiltration, renal deterioration cannot be dissociated from a rise in systemic blood pressure. In patients with miscellaneous renal diseases and a depressed basal GFR there is indirect evidence that hyperfiltration might occur in some of the remnant glomeruli. However, at present there is little conclusive evidence to indicate that therapies which might normalize glomerular hemodynamics, e.g., dietary protein restriction, have any effect on progression of renal disease, or that angiotensin converting-enzyme inhibitors, which lower glomerular capillary pressure, have any advantage over other antihypertensive agents which are equally efficacious in lowering systemic blood pressure.     

Morphologic and functional changes in sympathetic nerve relationships with pancreatic alpha-cells after destruction of beta-cells in rats

Insulin-dependent diabetes mellitus (IDDM) in humans is accompanied by an attenuation of the response of glucagon to hypoglycemia. To identify an animal model of IDDM with alpha-cell unresponsiveness to glucopenia in which to pursue morphologic and in vitro functional investigation of the lesion, pancreases isolated from rats with IDDM induced by streptozocin (STZ) or occurring spontaneously in BB/W rats were perfused with buffer containing 150, 25, and 150 mg/dl of glucose. In both forms of IDDM the normal glucagon rise during glucopenia was markedly impaired, suggesting an abnormality comparable to that of human IDDM. Studies of the insular sympathetic apparatus were conducted in these rat models. Electron-microscopic examination of peri-insular nerve endings disclosed no discernible abnormality in either form of rat IDDM. However, morphometric analysis of contacts between [3H]norepinephrine-labeled sympathetic nerve terminals and alpha-cells in pancreases from STZ-induced diabetic (STZ-D) rats revealed a 65-70% reduction in direct contacts. An 80% reduction in the number of nerve endings (not labeled) in direct contact with alpha-cells was also noted in the BB/W diabetic rats. Norepinephrine reuptake, studied only in the STZ-D group, was not impaired. The availability of local endogenous norepinephrine to alpha-cells and their sensitivity to exogenous norepinephrine was determined by perfusing 2, 5, or 10 micrograms/ml of tyramine, a releaser of endogenous norepinephrine, and norepinephrine at a concentration that in pancreases from nondiabetic rats gave a quantitatively similar glucagon response.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nitric oxide synthase isoforms and glomerular hyperfiltration in early diabetic nephropathy

This study tested the hypothesis that nitric oxide (NO)-mediated renal vasodilation due to the activity of the inducible nitric oxide synthase (iNOS) contributes to glomerular hyperfiltration in diabetic rats. Two weeks after induction of diabetes mellitus by streptozotocin, mean arterial BP (MAP), GFR (inulin clearance), and renal plasma flow (RPF) (para-aminohippurate clearance) were measured in conscious instrumented rats. Diabetic rats had elevated GFR (3129 +/- 309 microl/min versus 2297 +/- 264 microl/min in untreated control rats, P < 0.05) and RPF (10526 +/- 679 microl/min versus 8005 +/- 534 microl/min), which was prevented by chronic insulin treatment. Intravenous administration of 0.1 and 1 mg of L-imino-ethyl-lysine (L-NIL), an inhibitor of iNOS, did not affect MAP, GFR, or RPF, either in diabetic or control rats. A higher L-NIL dose (10 mg) increased MAP and decreased RPF in diabetic rats significantly (n = 6, P < 0.05), but not in controls (n = 6). In addition, 0.1 mg of NG-nitro-L-arginine methyl ester (L-NAME), a nonselective blocker of NOS isoforms, decreased GFR (2389 +/- 478 microl/min) and RPF (7691 +/- 402 microl/min) in diabetic animals to control levels, while renal hemodynamics in normoglycemic rats were not altered. Higher L-NAME doses (1 and 10 mg) reduced GFR and RPF in diabetic and control rats to identical levels. In glomeruli isolated from diabetic and control rats, neither iNOS mRNA nor iNOS protein expression was detected. In contrast, increased protein levels of endothelial constitutive NOS (ecNOS) were found in glomeruli of diabetic rats compared with controls. By immunohistochemistry, ecNOS but not iNOS staining was observed in the endothelium of preglomerular vessels and in diabetic glomeruli. These results support the notion that increased NO availability due to greater abundance of ecNOS contributes to the pathogenesis of glomerular hyperfiltration in early experimental diabetic nephropathy. In contrast, we found no functional or molecular evidence for increased glomerular expression and activity of iNOS in diabetic rats.     

Cause of variable therapeutic efficiency of angiotensin converting enzyme inhibitor on glomerular lesions

We tested the effect of angiotensin I converting enzyme inhibitor (ACEI) on established glomerular sclerosis. Starting eight weeks after subtotal nephrectomy (sNPX), rats were given enalapril for four weeks in a dose of 50 (Group II, N = 5) or 200 mg/liter drinking water (Group III, N = 5). A third group of sNPX rats not given ACEI served as control (Group I, N = 10). Glomerular sclerosis index (S1, 0 to 4 scale) was assessed three-dimensionally on serial thin sections for individual glomeruli at biopsy (Bx, 8 weeks), and divided into four different ranks of severity and compared to autopsy (Ax, 12 weeks). In Group I control rats, 48% of the glomeruli at Bx had SI between 0 and 1 (rank 1, average: 0.49 +/- 0.06), 36% between 1 and 2 (rank 2, average: 1.53 +/- 0.06), 9% between 2 and 3 (rank 3, average: 2.45 +/- 0.12) and 7% between 3 and 4 (rank 4, average: 3.54 +/- 0.10). Glomeruli of the same rats at Ax were ranked according to severity of sclerosis, and then divided into percentile groups, corresponding to the percent of distribution at Bx. The 48% least sclerotic glomeruli at Ax had average SI of 0.69 +/- 0.08, the next 36% 2.58 +/- 0.11, and next 9% 3.97 +/- 0.02 and the most sclerotic 7% 4.00 +/- 0.00. Thus, sclerosis advanced during the last four weeks after biopsy in all glomeruli, with more accelerated progression occurring toward later stages of sclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)