Targeted overexpression of protein kinase C beta2 isoform in myocardium causes cardiomyopathy

Increased cardiovascular mortality occurs in diabetic patients with or without coronary artery disease and is attributed to the presence of diabetic cardiomyopathy. One potential mechanism is hyperglycemia that has been reported to activate protein kinase C (PKC), preferentially the beta isoform, which has been associated with the development of micro- and macrovascular pathologies in diabetes mellitus. To establish that the activation of the PKCbeta isoform can cause cardiac dysfunctions, we have established lines of transgenic mice with the specific overexpression of PKCbeta2 isoform in the myocardium. These mice overexpressed the PKCbeta2 isoform transgene by 2- to 10-fold as measured by mRNA, and proteins exhibited left ventricular hypertrophy, cardiac myocyte necrosis, multifocal fibrosis, and decreased left ventricular performance without vascular lesions. The severity of the phenotypes exhibited gene dose-dependence. Up-regulation of mRNAs for fetal type myosin heavy chain, atrial natriuretic factor, c-fos, transforming growth factor, and collagens was also observed. Moreover, treatment with a PKCbeta-specific inhibitor resulted in functional and histological improvement. These findings have firmly established that the activation of the PKCbeta2 isoform can cause specific cardiac cellular and functional changes leading to cardiomyopathy of diabetic or nondiabetic etiology.

Characterization of protein kinase C beta isoform activation on the gene expression of transforming growth factor-beta, extracellular matrix components, and prostanoids in the glomeruli of diabetic rats

Induction of protein kinase C (PKC) pathway in the vascular tissues by hyperglycemia has been associated with many of the cellular changes observed in the complications of diabetes. Recently, we have reported that the use of a novel, orally effective specific inhibitor of PKC beta isoform (LY333531) normalized many of the early retinal and renal hemodynamics in rat models of diabetes. In the present study, we have characterized a spectrum of biochemical and molecular abnormalities associated with chronic changes induced by glucose or diabetes in the cultured mesangial cells and renal glomeruli that can be prevented by LY333531. Hyperglycemia increased diacylglycerol (DAG) level in cultured mesangial cells exposed to high concentrations of glucose and activated PKC alpha and beta1 isoforms in the renal glomeruli of diabetic rats. The addition of PKC beta selective inhibitor (LY333531) to cultured mesangial cells inhibited activated PKC activities by high glucose without lowering DAG levels and LY333531 given orally in diabetic rats specifically inhibited the activation of PKC beta1 isoform without decreasing PKC alpha isoform activation. Glucose-induced increases in arachidonic acid release, prostaglandin E2 production, and inhibition of Na+-K+ ATPase activities in the cultured mesangial cells were completely prevented by the addition of LY333531. Oral feeding of LY333531 prevented the increased mRNA expression of TGF-beta1 and extracellular matrix components such as fibronectin and alpha1(IV) collagen in the glomeruli of diabetic rats in parallel with inhibition of glomerular PKC activity. These results suggest that the activation of PKC, predominately the beta isoform by hyperglycemia in the mesangial cells and glomeruli can partly contribute to early renal dysfunctions by alteration of prostaglandin production and Na+-K+ ATPase activity as well as the chronic pathological changes by the overexpression of TGF-beta1 and extracellular matrix components genes.

Prevention of glomerular dysfunction in diabetic rats by treatment with d-alpha-tocopherol

Because d-alpha-tocopherol (vitamin E) has been shown to decrease diacylglycerol (DAG) levels and prevent the activation of protein kinase C (PKC), which is associated with retinal and renal dysfunctions in diabetes, the study presented here characterized the effect of d-alpha-tocopherol treatment to prevent glomerular hyperfiltration and increased albuminuria as well as PKC activities in streptozotocin (STZ)-induced diabetic rats. Two weeks after the induction of diabetes, total DAG content and PKC activity in glomeruli were significantly increased in diabetic rats by 106.4 +/- 16.8% and 66.4 +/- 8.4%, respectively, compared with control rats. Intraperitoneal injection of d-alpha-tocopherol (40 mg/kg of body weight) every other day prevented the increases in total DAG content and PKC activity in glomeruli of diabetic rats. Glomerular filtration rate (GFR) and filtration fraction (FF) were significantly elevated to 4.98 +/- 0.34 mL/min and 0.36 +/- 0.05, respectively, in diabetic rats, compared with 2.90 +/- 0.14 mL/min and 0.25 +/- 0.02, respectively, in control rats. These hemodynamic abnormalities in diabetic rats were normalized to 2.98 +/- 0.09 mL/min and 0.24 +/- 0.01, respectively, by d-alpha-tocopherol. Albuminuria in 10-wk diabetic rats was significantly increased to 9.1 +/- 2.2 mg/day compared with 1.2 +/- 0.3 mg/day in control rats, whereas d-alpha-tocopherol treatment improved albumin excretion rate to 2.4 +/- 0.6 mg/day in diabetic rats. To clarify the mechanism of d-alpha-tocopherol's effect on DAG-PKC pathway, the activity and protein levels of DAG kinase alpha and gamma, which metabolize DAG to phosphatidic acid, were examined. Treatment with d-alpha-tocopherol increased DAG kinase activity in the glomeruli of both control and diabetic rats, by 22.6 +/- 3.6% and 28.5 +/- 2.3% respectively, although no differences were observed in the basal DAG kinase activity between control and diabetic rats. Because immunoblotting studies did not exhibit any difference in the protein levels of DAG kinase alpha and gamma, the effect of d-alpha-tocopherol is probably modulating the enzyme kinetics of DAG kinase. These findings suggest that the increases in DAG-PKC pathway play an important role for the development of glomerular hyperfiltration and increased albuminuria in diabetes and that d-alpha-tocopherol treatment could be preventing early changes of diabetic renal dysfunctions by normalizing the increases in DAG and PKC levels in glomerular cells.

Differential inhibition of mesangial MAP kinase cascade by cyclic nucleotides

The agents which increase intracellular cyclic AMP (cAMP) or cyclic GMP (cGMP) have been found to counteract the effects of the vasoconstrictive agents such as endothelin-1 (ET-1). To clarify the mechanism of this interaction, we evaluated the activities of mitogen-activated protein kinase (MAPK) cascade, one of the important signal transduction system of ET-1. Beraprost sodium, an analogue of PGI2, and adrenomedullin, a cAMP-raising agent, inhibited ET-1-induced activation of MAPK. Dibutyryl cAMP (Bt2-cAMP) and 8-bromo-cGMP (8-Br-cGMP), cell permeable analogues of cAMP and cGMP, were also able to inhibit the activation of MAPK and MAPK kinase (MAPKK) by ET-1 without interfering basal activities. In contrast, phorbol 12, 13-dibutylate (PDBu)-induced activation of MAPK and MAPKK was inhibited by Bt2-cAMP but not by 8-Br-cGMP. Interestingly, atrial natriuretic peptide (ANP) partially inhibited PDBu-induced activation of MAPK and MAPKK. These results indicate that cAMP and cGMP inhibit ET-1-induced activation of MAPK in cultured mesangial cells at different steps; the former might inhibit at a step downstream of PKC and the latter prior to PKC. The data also suggest that ANP might have cGMP-independent effect on MAPK.

Amelioration of vascular dysfunctions in diabetic rats by an oral PKC beta inhibitor

The vascular complications of diabetes mellitus have been correlated with enhanced activation of protein kinase C (PKC). LY333531, a specific inhibitor of the beta isoform of PKC, was synthesized and was shown to be a competitive reversible inhibitor of PKC beta 1 and beta 2, with a half-maximal inhibitory constant of approximately 5 nM; this value was one-fiftieth of that for other PKC isoenzymes and one-thousandth of that for non-PKC kinases. When administered orally, LY333531 ameliorated the glomerular filtration rate, albumin excretion rate, and retinal circulation in diabetic rats in a dose-responsive manner, in parallel with its inhibition of PKC activities.

Endothelin-1 stimulates tyrosine phosphorylation of p125 focal adhesion kinase in mesangial cells

Endothelin-1 (ET-1) is known to induce the contraction and proliferation of glomerular mesangial cells. Because ET-1 was found to stimulate the tyrosine phosphorylation of unidentified cellular proteins in cultured mesangial cells, protein tyrosine kinase might serve as one of the important signals leading to various functions of ET-1. Focal adhesion kinase (p125FAK) is a newly identified cytoplasmic protein tyrosine kinase that is activated by the phosphorylation of its own tyrosine residue. Because p125FAK was found to play a role in the signal transduction of not only integrins but also various neurotransmitters, including bombesin, endothelin, and vasopressin in Swiss 3T3 cells and Rat-1 fibroblasts, whether ET-1 could stimulate the tyrosine phosphorylation of p125FAK in glomerular mesangial cells was examined. ET-1 stimulated the tyrosine phosphorylation of p125FAK by threefold to fourfold in cultured mesangial cells. This effect of ET-1 was detected at 1 min and reached a maximum within 5 min and was blocked by BQ-123, an antagonist for ETA receptor. A23187, a calcium ionophore, failed to stimulate the tyrosine phosphorylation of p125FAK, and ET-1 was able to stimulate the tyrosine phosphorylation of p125FAK, even in a calcium-free medium. The activation of protein kinase C (PKC) by phorbol 12, 13-dibutyrate resulted in a stimulation of the tyrosine phosphorylation of p125FAK, and an inhibition of PKC by calphostin C or staurosporine significantly reduced the effect of ET-1. Furthermore, prolonged treatment of the cells with phorbol 12, 13-dibutyrate markedly inhibited the ET-1-induced tyrosine phosphorylation of p125FAK. These results indicate that p125FAK might play a role in a signal transduction system of ET-1 in glomerular mesangial cells and that the ET-1-induced tyrosine phosphorylation of p125FAK is largely dependent on the PKC pathway.

Abnormalities in protein kinase C and MAP kinase cascade in mesangial cells cultured under high glucose conditions

In order to clarify the mechanism of mesangial cell dysfunction in diabetes, we examined the activities of protein kinase C (PKC) and mitogen-activated protein kinase (MAPK), important kinases in various cellular functions, and also evaluated the isoenzymes of PKC in mesangial cells cultured under high glucose conditions. Exposure of cells to high concentrations (27.8 mM) of glucose for 5 days resulted in a significant elevation of PKC activities in the membrane fraction. MAPK was also activated in cells cultured under high glucose conditions. Of the PKC isoenzymes, the levels of PKC alpha and zeta were significantly increased in the membrane fraction after 5 days of exposure to high concentrations of glucose. These results indicate that the translocation of PKC alpha and zeta and the activation of MAPK under high glucose conditions might be underlying mechanisms of the functional disturbance of mesangial cells in diabetes.

Microalbuminuria cannot predict cardiovascular death in Japanese subjects with non-insulin-dependent diabetes mellitus

In order to examine whether the existence of microalbuminuria can predict the development of overt proteinuria and cardiovascular death in Japanese subjects with non-insulin-dependent diabetes mellitus (NIDDM), we investigated 47 patients for a 10-year follow-up period. Patients were divided into two groups by the initial values of urinary albumin excretion rates. The percentage of patients who developed overt proteinuria during the follow-up period was significantly higher in patients who were initially classified as microalbuminuric group (63.6%) than in normoalbuminuric group (17.4%). During the follow-up period, one of the patients with normoalbuminuria had died of congestive heart failure, while four of those with microalbuminuria had died; one of stroke and three from noncardiovascular diseases. These results indicate that the existence of microalbuminuria had the predictive power for the development of overt proteinuria, but not for cardiovascular death in Japanese subjects with NIDDM.

Identification and characterization of a gene regulating enzymatic glycosylation which is induced by diabetes and hyperglycemia specifically in rat cardiac tissue

Primary cardiac abnormalities have been frequently reported in patients with diabetes probably due to metabolic consequences of the disease. Approximately 2,000 mRNA species from the heart of streptozotocin-induced diabetic and control rats were compared by the mRNA differential display method, two of eight candidate clones thus isolated (DH1 and 13) were confirmed by Northern blot analysis. The expression of clone 13 was increased in the heart by 3.5-fold (P < 0.05) and decreased in the aorta by twofold (P < 0.05) in diabetes as compared to control. Sequence analysis showed that clone 13 is a rat mitochondrial gene. DH1 was predominantly expressed in the heart with an expression level 6.8-fold higher in the diabetic rats than in control (P < 0.001). Insulin treatment significantly (P < 0.001) normalized the expression of DH1 in the hearts of diabetic rats. DH1 expression was observed in cultured rat cardiomyocytes, but not in aortic smooth muscle cells or in cardiac derived fibroblasts. The expression in cardiomyocytes was regulated by insulin and glucose concentration of culture media. The full length cDNA of DH1 had a single open-reading frame with 85 and 92% amino acid identity to human and mouse UDP-GlcNAc:Gal beta 1-3GalNAc alpha R beta 1-6 N-acetylglucosaminyltransferase (core 2 GlcNAc-T), respectively, a key enzyme determining the structure of O-linked glycosylation. Transient transfection of DH1 cDNA into Cos7 cells conferred core 2 GlcNAc-T enzyme activity. In vivo, core 2 GlcNAc-T activity was increased by 82% (P < 0.05) in diabetic hearts vs controls, while the enzymes GlcNAc-TI and GlcNAc-TV responsible for N-linked glycosylation were unchanged. These results suggest that core 2 GlcNAc-T is specifically induced in the heart by diabetes or hyperglycemia. The induction of this enzyme may be responsible for the increase in the deposition of glycoconjugates and the abnormal functions found in the hearts of diabetic rats.

Cyclic nucleotides attenuate endothelin-1-induced activation of mitogen-activated protein kinase in cultured rat mesangial cells

In order to clarify the mechanisms of interaction between endothelin-1 (ET-1) and cyclic AMP (cAMP) or cyclic GMP (cGMP), we examined the effects of cAMP or cGMP on ET-1-induced activation of mitogen-activated protein kinase (MAPK), one of the key enzymes in the signal transduction of ET-1, in cultured rat mesangial cells. ET-1 was able to activate both p42 and p44 MAP kinases in a dose-dependent manner. Cell permeable analogues of cAMP and cGMP, dibutylyl cAMP (BT2-cAMP) and 8 bromo cGMP (8br-GMP), significantly inhibited ET-1-induced activation of MAPK. Atrial natriuretic peptide (ANP), which increased cellular cGMP, was able to inhibit ET-1-induced activation of MAPK in a dose-dependent manner, while c-ANP, an analogue specific to the clearance receptors of ANP, exerted no effect. These results indicate that cAMP and cGMP could modulate the action of ET-1 in mesangial cells at a step of the activation of MAPK.

Translocation of protein kinase C alpha and zeta in rat glomerular mesangial cells cultured under high glucose conditions

The activities and expression of protein kinase C isoenzymes were examined in glomerular mesangial cells cultured under high glucose conditions. Exposure of cells to high glucose concentrations (27.8 mmol/l) for more than 3 days resulted in a significant elevation of protein kinase C activities in the membrane fraction. Of the protein kinase C isoenzymes, the levels of protein kinase C alpha significantly increased in the membrane fraction after 3 days of exposure to glucose, and protein kinase C zeta increased after 5 days of exposure. Levels of protein kinase C delta and epsilon remained unchanged and protein kinase, C beta and gamma were not detected. These results indicate that protein kinase C alpha and zeta are translocated under high glucose conditions possibly through different mechanisms.

[A case of pulmonary sarcoidosis associated with severe hypercalcemia]

A 71-year-old man with a history of sarcoidosis was admitted to our hospital because of polyuria and polydipsia. On admission, the serum calcium concentration was elevated to 12.7mg/dl, and the creatinine clearance was 28.3ml/min. The initial serum 1,25-dihydroxyvitamin D concentration was 55.0pg/ml, while angiotensin-converting enzyme activity and serum PTH-rP concentration were within the normal range. Radiological studies revealed enlargement of bilateral hilar lymph nodes and a nodular lesion in the right lower lung field. Transbronchial lung biopsy showed noncaseous granuloma consistent with pulmonary sarcoidosis. After oral administration of 20mg prednisolone daily, the serum calcium and 1,25-dihydroxyvitamin D concentration returned to normal, and creatinine clearance was raised to 55ml/min. In conclusion, low dose glucocorticoid administration successfully reduced serum 1,25-dihydroxyvitamin D level with a prompt decrease in serum calcium level in a patient with sarcoidosis.

Alteration of mesangial response to ANP and angiotensin II by glucose

To test the hypothesis that the function of glomerular mesangial cells is impaired in diabetes, we examined the responsiveness of mesangial cells cultured under high concentrations of glucose to atrial natriuretic peptide (ANP1) and angiotensin II (Ang II). The ANP-induced accumulation of cGMP was enhanced in mesangial cells cultured under high glucose conditions, possibly due to the activation of particulate guanylate cyclase. Ang II action in mesangial cells was evaluated by measuring the ability of Ang II to inhibit ANP-induced cGMP accumulation through both activating phosphodiesterase (initial phase) and inhibiting guanylate cyclase (maintenance phase). The inhibition of both ANP-induced cellular cGMP accumulation and particulate guanylate cyclase activity by Ang II was significantly reduced in mesangial cells cultured under high concentrations of glucose. Moreover, in the cells exposed to high concentrations of glucose, both basal and Ang II-stimulated levels of inositol 1,4,5-trisphosphate (IP3) were significantly reduced. These results indicate that, in high glucose conditions, the actions of ANP and Ang II are modulated differently, resulting in the impairment of contractile responsiveness of mesangial cells.

Antagonist for atrial natriuretic peptide receptors ameliorates glomerular hyperfiltration in diabetic rats

To evaluate the possible contribution of atrial natriuretic peptide (ANP) to the development of glomerular hyperfiltration, we examined the effect of non-peptide competitive antagonist for biological receptors of ANP, HS-142-1, on glomerular filtration rate (GFR) and renal plasma flow (RPF) in diabetic rats. Increased GFR and RPF in diabetic rats were significantly ameliorated by the injection of HS-142-1, while blood pressure remained unchanged. Urinary cyclic GMP excretion was significantly higher in diabetic rats than in control rats and HS-142-1 decreased urinary cGMP excretion significantly. These results indicate that atrial natriuretic peptide contributes to the development of glomerular hyperfiltration and hyperperfusion in diabetes and HS-142-1 might be useful in the treatment of them.

Biological receptors mediate anti-proliferative action of atrial natriuretic peptide in cultured mesangial cells

The mechanism of anti-proliferative action of atrial natriuretic peptide (ANP) was examined in cultured mesangial cells. HS-142-1, a selective antagonist for ANP biological receptors, inhibited ANP-induced cellular cGMP accumulation and prevented ANP-induced inhibition of both serum-stimulated incorporation of 3H-thymidine and cell proliferation. Des-[Gln18, Ser19, Gly20, Leu21, Gly22]-ANP4-23-NH2 (C-ANP) failed to inhibit 3H-thymidine incorporation. These results indicate that anti-proliferative action of ANP is mediated by the biological receptors in cultured mesangial cells.

Differential modulation of mitogenic and metabolic actions of insulin-like growth factor I in rat glomerular mesangial cells in high glucose culture

In order to explore the possible contribution of insulin-like growth factor I to the development of diabetic nephropathy, the effect of glucose on the mitogenic and metabolic actions of insulin-like growth factor I in cultured rat glomerular mesangial cells was examined. The stimulation of [3H]-thymidine incorporation by insulin-like growth factor I in the cells exposed to high concentrations (55 mmol/l) of glucose (4.6 +/- 1.3 fold stimulation) was significantly suppressed as compared with that in the cells cultured in 11 mmol/l glucose (17.5 +/- 0.8 fold). In contrast, [3H]-amino-isobutylic acid uptake into the mesangial cells was significantly enhanced by glucose (2.03 +/- 0.03 nmol.mg protein-1. 15 min-1 at 55 mmol/l glucose vs 0.59 +/- 0.01 at 11 mmol/l glucose), while 2-deoxyglucose uptake remained unchanged. [125I]-insulin-like growth factor I binding was slightly but significantly increased in the cells exposed to high concentrations of glucose. Thus, glucose may modulate the mitogenic and metabolic actions of insulin-like growth factor I differently in cultured mesangial cells probably at the post-insulin-like growth factor I receptor level. These results may indicate that the differential modulation of the actions of insulin-like growth factor I by glucose could result in the increase in amino acid uptake and decrease in the cell proliferation in the mesangial cells, possibly leading to enhanced mesangial matrix synthesis with a relatively small increase in mesangial cell volume as seen in diabetic nephropathy.

Nipradilol inhibits rat mesangial cell mitogenesis through the activation of soluble guanylate cyclase

Nipradilol is a beta-adrenoreceptor blocking agent, whose structure contains an NO2 group. Thus, it is possible that it modulates the function of glomerular mesangial cells through the activation of soluble guanylate cyclase. To prove this hypothesis, we examined the effect of nipradilol on soluble guanylate cyclase, intracellular cyclic guanosine monophosphate (cGMP) accumulation, and the mitogenesis of cultured rat glomerular mesangial cells. Nipradilol increased intracellular cGMP accumulation in a dose-dependent manner through the activation of soluble guanylate cyclase. Furthermore, nipradilol inhibited the incorporation of [3H]thymidine into the mesangial cells stimulated by 2.5% fetal bovine serum in a dose-dependent manner. These results indicate that nipradilol may modulate mesangial cell function through an increase in intracellular cGMP resulting from the activation of soluble guanylate cyclase.

High blood pressure is a risk factor for the development of microalbuminuria in Japanese subjects with non-insulin-dependent diabetes mellitus

In this study, 52 nonproteinuric Japanese patients with non-insulin-dependent diabetes (NIDDM) were followed from 1985 to 1990 to investigate the rate of development and progression of microalbuminuria and the factors which influence it. In 1985, 34 patients were normoalbuminuric, and 18 patients were microalbuminuric. Five years later, 11 of 34 initially normoalbuminuric patients (32.4%) developed microalbuminuria, and 6 of 18 initially microalbuminuric patients (33.3%) developed overt proteinuria. At the beginning of the study, hypertension existed more frequently in the patients who later developed microalbuminuria (8 of 11, 72.7%) than in the patients who stayed normoalbuminuric (4 of 23, 17.4%). Age-adjusted values of mean blood pressure (+/- SEM) at the beginning of the study in the patients who developed microalbuminuria (98.2 +/- 3.4 mm Hg, n = 11) were significantly higher than those in the patients who stayed normoalbuminuric (87.3 +/- 2.4 mm Hg, n = 23). In six patients who developed overt proteinuria, initial urinary albumin excretion rates (AER) were higher than those in the patients who stayed microalbuminuric, and four patients who presented with initial AER greater than 100 micrograms/min all developed overt proteinuria. These results indicate that, in Japanese patients with NIDDM, the rate of development of microalbuminuria is faster than that reported in Caucasian IDDM, and preexisting hypertension with relatively poor control of blood pressure may be a risk factor for the development of microalbuminuria.

Metabolic actions of insulin-like growth factor I in cultured glomerular mesangial cells

Glomerular mesangial cells in culture have been reported to possess a considerable number of receptors specific to insulin-like growth factor I (IGF-I), with very small number of receptors specific to insulin. To explore acute metabolic effects of IGF-I on mesangial cells, uptake of glucose and amino acid was measured in the presence of IGF-I or insulin. IGF-I stimulated D-[U-14C]glucose incorporation, 2-deoxy[1-3H]glucose uptake and alpha-[methyl-3H]aminoisobutyric acid (AIB) uptake into cultured mesangial cells by 139.8% +/- 2.1%, 116.6% +/- 1.7%, and 214.9% +/- 12.8% (percent of basal), respectively. Similar maximal stimulation was also induced by insulin, while the ED50 of IGF-I to stimulate these uptake systems (9.98 +/- 2.36, 3.45 +/- 1.86, and 3.35 +/- 0.40 ng/mL, respectively) was significantly lower than that of insulin (120.8 +/- 28.5, 61.8 +/- 7.7, and 76.3 +/- 17.5, respectively). These results indicate that, in cultured glomerular mesangial cells, IGF-I induces acute metabolic effects, possibly through its own receptors.

Reduced activity of renal angiotensin-converting enzyme in streptozotocin-induced diabetic rats

To clarify the possible role of intrarenal renin-angiotensin system (RAS) in the evolution of renal hemodynamic alteration in diabetes, we investigated the change of tissue angiotensin-converting enzyme (ACE) activity, a key enzyme of RAS, in the kidneys obtained from streptozotocin-induced diabetic rats. Tissue ACE activity was significantly reduced in both outer cortex (0.29 +/- 0.04, mean +/- SEM, n = 6) and inner cortex with outer medulla (2.43 +/- 0.28, n = 6) of the kidneys from diabetic rats 2 weeks after induction of diabetes compared with those from control rats (0.47 +/- 0.05, n = 7, in outer cortex; 3.68 +/- 0.32, n = 7, in inner cortex with outer medulla). ACE activities in the lung and aorta of diabetic rats were not different from those of control rats. ACE activities in the serum and urine were significantly elevated in diabetic rats. Treatment of diabetic rats with insulin to achieve near euglycemia completely prevented these alterations in ACE activity, except that, in the urine, the elevation of ACE was partially corrected with insulin. In contrast to ACE activity, activity of N-acetyl-beta-D-glucosaminidase (a lysosomal enzyme of the tubule) and r-glutamyl transpeptidase (a brush border enzyme) in the kidney were not reduced in diabetic rats, whereas in the urine both enzyme activities were significantly elevated in diabetic rats. It is likely, therefore, that the reduction of ACE activity in the kidneys of diabetic rats may reflect the impairment of vascular endothelial cells in the kidney, rather than tubular damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Dual mechanism of angiotensin II inhibits ANP-induced mesangial cGMP accumulation

To evaluate an interaction between vasoconstrictive (Ang II) and vasodilating (ANP) peptides, we examined the effect of Ang II on ANP-induced accumulation of cGMP in cultured glomerular mesangial cells. ANP rapidly increased intracellular cGMP levels, with a peak stimulation at one minute in the absence of IBMX and at ten minutes in the presence of IBMX. The ANP-induced cGMP accumulation was significantly inhibited when the cells were treated with Ang II simultaneously with ANP for one minute in the absence of IBMX. This inhibitory effect of Ang II was completely abolished by IBMX and significantly reduced in calcium-free media or by W7, but not affected by H7. Similar inhibitory effect was observed when cells were treated with A23187 but not with TPA for one minute. In the presence of IBMX, Ang II inhibited ANP-induced cGMP accumulation when cells were treated with Ang II for 15 minutes prior to the stimulation by ANP. This inhibition by Ang II was blocked by H7. ANP-induced increase in particulate guanylate cyclase activity was significantly reduced in the cells treated with Ang II or TPA. This reduction of enzyme activity was also prevented by H7. These results indicate that Ang II inhibits ANP-induced cGMP accumulation in cultured glomerular mesangial cells through at least two mechanisms; one is the activation of calcium-dependent, calmodulin-stimulated cyclic nucleotide phosphodiesterase in the initial phase, and the other is the inhibition of guanylate cyclase resulting from protein kinase C activation in the maintenance phase.