Thromboxane stimulation of mesangial cell fibronectin synthesis is signalled by protein kinase C and modulated by cGMP

Requirement for sphingosine kinase 1 in mediating phase 1 of the hypotensive response to anandamide in the anaesthetised mouse

In the isolated rat carotid artery, the endocannabinoid anandamide induces endothelium-dependent relaxation via activation of the enzyme sphingosine kinase (SK). This generates sphingosine-1-phosphate (S1P) which can be released from the cell and activates S1P receptors on the endothelium. In anaesthetised mice, anandamide has a well-characterised triphasic effect on blood pressure but the contribution of SK and S1P receptors in mediating changes in blood pressure has never been studied. Therefore, we assessed this in the current study.

The peak hypotensive response to 1 and 10 mg/kg anandamide was measured in control C57BL/6 mice and in mice pretreated with selective inhibitors of SK1 (BML-258, also known as SK1-I) or SK2 ((R)-FTY720 methylether (ROMe), a dual SK1/2 inhibitor (SKi) or an S1P₁ receptor antagonist (W146). Vasodilator responses to S1P were also studied in isolated mouse aortic rings.

The hypotensive response to anandamide was significantly attenuated by BML-258 but not by ROMe. Antagonising S1P₁ receptors with W146 completely blocked the fall in systolic but not diastolic blood pressure in response to anandamide. S1P induced vasodilation in denuded aortic rings was blocked by W146 but caused no vasodilation in endothelium-intact rings.

This study provides evidence that the SK1/S1P regulatory-axis is necessary for the rapid hypotension induced by anandamide. Generation of S1P in response to anandamide likely activates S1P₁ to reduce total peripheral resistance and lower mean arterial pressure. These findings have important implications in our understanding of the hypotensive and cardiovascular actions of cannabinoids.

Clarithromycin inhibits fibroblast migration

The aim of the current study was to investigate the effect of 14-membered ring macrolide clarithromycin (CAM) on migration induced by human plasma fibronectin (HFn) or on contraction of human fetal lung fibroblasts (HFL-1).

METHODS AND RESULTS

Using the blindwell chamber technique, CAM (10(-5) M) inhibited the migration of HFL-1 60.2+/-4.0% (p<0.05). Other antibiotics, such as ampicillin, minocycline or azithromycin had no effects on HFL-1 migration. The effect of CAM was concentration dependent. HFL-1 migration, stimulated by TXA(2) analog was also inhibited by CAM. Clarithromycin had no effect on HFL-1 mediated gel contraction that was another function of fibroblast at the wound area.

CONCLUSIONS

Clarithromycin may contribute to the regulation of the wound healing response following injury by inhibiting fibroblast migration. These results could represent the therapeutic benefits of CAM.

Pathogenic role of nitric oxide alterations in diabetic nephropathy

Diabetic nephropathy is the most frequent cause of terminal renal failure, requiring renal replacement therapy. Although a number of factors may contribute to the development of renal disease in diabetes, the recent past has witnessed an explosive growth in literature pertaining to the role of nitric oxide in diabetic nephropathy. However, there are significant controversies in the findings of these studies partly because of the complex metabolic pathways involved in the generation and fate of nitric oxide in the diabetic kidney. The following discussion presents a critical and balanced review of the current understanding of this subject.

From hyperglycemia to diabetic kidney disease: the role of metabolic, hemodynamic, intracellular factors and growth factors/cytokines

At present, diabetic kidney disease affects about 15-25% of type 1 and 30-40% of type 2 diabetic patients. Several decades of extensive research has elucidated various pathways to be implicated in the development of diabetic kidney disease. This review focuses on the metabolic factors beyond blood glucose that are involved in the pathogenesis of diabetic kidney disease, i.e., advanced glycation end-products and the aldose reductase system. Furthermore, the contribution of hemodynamic factors, the renin-angiotensin system, the endothelin system, and the nitric oxide system, as well as the prominent role of the intracellular signaling molecule protein kinase C are discussed. Finally, the respective roles of TGF-beta, GH and IGFs, vascular endothelial growth factor, and platelet-derived growth factor are covered. The complex interplay between these different pathways will be highlighted. A brief introduction to each system and description of its expression in the normal kidney is followed by in vitro, experimental, and clinical evidence addressing the role of the system in diabetic kidney disease. Finally, well-known and potential therapeutic strategies targeting each system are discussed, ending with an overall conclusion.

Characterization of the PGI2/IP system in cultured rat mesangial cells

Mesangial cells play an important role in glomerular function. They are an important source of cyclooxygenase (COX)-derived arachidonic acid metabolites, including prostaglandin E(2) and prostacyclin. Prostacyclin receptor (IP) mRNA was amplified from cultured mesangial cell total RNA by RT-PCR. While the prostaglandin E(2) receptor subtype EP(2) was not detected, EP(1,3,4) mRNA was amplified. Also, IP protein was noted in mesangial cells, proximal tubules, inner medullary collecting ducts, and the inner and outer medulla. But no protein was detected in whole cortex preparations. Prostacyclin analogues: cicaprost and iloprost, increased cAMP levels in mesangial cells. On the other hand, arginine-vasopressin and angiotensin II increased intracellular calcium in mesangial cells, but cicaprost, iloprost and prostaglandin E(2) had no effect. Moreover, a 50% inhibition of cicaprost- and iloprost-cAMP stimulation was observed upon mesangial cell exposure to 25 and 35 mM glucose for 5 days. But no change in IP mRNA was observed at any glucose concentration or time exposure. Although 25 mM glucose had no effect on COX-1 protein levels, COX-2 was increased up to 50%. In contrast, PGIS levels were reduced by 50%. Thus, we conclude that the prostacyclin/IP system is present in cultured rat mesangial cells, coupling to a cAMP stimulatory pathway. High glucose altered both enzymes in the PGI(2) synthesis pathway, increasing COX-2 but reducing PGIS. In addition, glucose diminished the cAMP response to prostacyclin analogues. Therefore, glucose attenuates the PGI(2)/IP system in cultured rat mesangial cells.

Protein kinase C-zeta modulates thromboxane A(2)-mediated apoptosis in adult ventricular myocytes via Akt

We hypothesized that thromboxane A(2) (TxA(2)) receptor stimulation directly induces apoptosis in adult cardiac myocytes. To investigate this, we exposed cultured adult rat ventricular myocytes (ARVM) to a TxA(2) mimetic [1S-[1alpha,2alpha(Z),3beta(1E,3S*),4alpha]]-7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (I-BOP) for 24 h. Stimulation with I-BOP induced apoptosis in a dose-dependent manner and was completely prevented by a TxA(2) receptor antagonist, SQ-29548. We further investigated the role of protein kinase C (PKC) in this process. TxA(2) stimulation resulted in membrane translocation of PKC-zeta but not PKC-alpha, -betaII, -delta, and -epsilon at 3 min and 1 h. The activation of PKC-zeta by I-BOP was confirmed using an immune complex kinase assay. Treatment of ARVM with a cell-permeable PKC-zeta pseudosubstrate peptide (zeta-PS) significantly attenuated apoptosis by I-BOP. In addition, I-BOP treatment decreased baseline Akt activity and its decrease was reversed by treatment with zeta-PS. The inhibition of phosphatidylinositol 3-kinase upstream of Akt by wortmannin or LY-294002 abolished the antiapoptotic effect of zeta-PS. Therefore, our results suggest that the activation of PKC-zeta modulates TxA(2) receptor-mediated apoptosis at least, in part, through Akt activity in adult cardiac myocytes.

Novel approaches to the treatment of progressive renal disease

Diabetes and hypertension are major contributors to the increasing incidence of progressive renal disease. In addition to more potent antihypertensive agents that block the renin-angiotensin system, drugs that modulate other pathogenetic pathways are also in development. Recent preclinical studies indicate that compounds that interfere with the formation and action of advanced glycation end products may have a role in the treatment and prevention of diabetic nephropathy, as may agents targeting the activity of protein kinase C.

Lupus nephritis: lessons from experimental animal models

Lupus nephritis is a frequent and severe complication of SLE. In the last decades, animal models for SLE have been studied widely to investigate the immunopathology of this autoimmune disease because abnormalities can be studied and manipulated before clinical signs of the disease become apparent. In this review an overview is given of our current knowledge on the development of lupus nephritis, as derived from animal models, and a hypothetical pathway for the development of lupus nephritis is postulated. The relevance of the studies in experimental models in relationship with our knowledge of human SLE is discussed.

Roles of prostaglandin E receptors in mesangial cells under high-glucose conditions

BACKGROUND

High glucose reportedly stimulates prostaglandin (PG) E2 production and DNA synthesis in mesangial cells (MCs). However, the pathophysiological significance of PGE2 in MCs has remained unclear.

METHODS

The effects of prostanoids on [3H]-thymidine uptake and cAMP production in rat MCs cultured with 5.6 mM glucose, 25 mM glucose, or 5.6 mM glucose supplemented with 19.4 mM mannitol were examined. The gene expression of PGE2 receptor (EP) subtypes in MCs was analyzed with Northern blotting techniques.

RESULTS

Northern blotting indicated EP1 and EP4 gene expression in MCs. EP1 agonists and PGE2 stimulated [3H]-thymidine uptake in MCs. EP1 antagonists dose dependently attenuated high-glucose-induced [3H]-thymidine uptake, which suggests EP1 involvement, by an increase in intracellular Ca2+, in DNA synthesis of MCs. On the other hand, forskolin, db-cAMP, and 11-deoxy-PGE1, an EP4/EP3/EP2 agonist, significantly decreased DNA synthesis in MCs. These inhibitory effects are thought to be mediated via EP4 as a result of an increase in cAMP synthesis. The effects via EP4 seem to be particularly important because PGE2-induced cAMP synthesis was significantly attenuated in the high-glucose group compared with the mannitol group, in which [3H]-thymidine uptake did not increase in spite of augmented PGE2 production.

CONCLUSION

The increase in DNA synthesis in MCs under high-glucose conditions can be explained, at least in part, by the high-glucose-induced inhibition of cAMP production via EP4, which augments EP1 function in conjunction with the overproduction of PGE2.

Thromboxane A2 modulates the fibrinolytic system in glomerular mesangial cells

We examined the effects of thromboxane A2 (TxA2) on the activities of the plasminogen-plasmin system in glomerular mesangial cells. When mesangial cells are exposed to the TxA2 agonist U-46619, a substantial increase in production of plasminogen activator inhibitor-1 (PAI-1) protein is observed that is significantly greater than that induced by 10% serum alone. This increase in PAI-1 protein production is accompanied by an increase in steady-state levels of PAI-1 mRNA. This stimulation is specifically mediated by TxA2 (thromboxane prostanoid, TP) receptors, since U-46619 also stimulates PAI-1 expression in cells that are transfected with TP receptors, and this stimulation of PAI-1 production is completely blocked by the TxA2 receptor antagonist, SQ-29,548. Despite the increase in PAI-1 production, there was net stimulation of plasmin activity in the medium of mesangial cells that had been exposed to U-46619. Furthermore, U-46619 also caused an increase in tissue plasminogen activator (tPA) mRNA levels. Thus TxA2 stimulates the production of PAI-1 and plasminogen activators by mesangial cells through a receptor-dependent mechanism. In inflammatory renal diseases, the balance of these effects may modulate glomerular thrombosis and renal fibrosis.

Glomerular mesangial cells: electrophysiology and regulation of contraction

Mesangial cells are smooth muscle-like pericytes that abut and surround the filtration capillaries within the glomerulus. Studies of the fine ultrastructure of the glomerulus show that the mesangial cell and the capillary basement membrane form a biomechanical unit capable of regulating filtration surface area as well as intraglomerular blood volume. Structural and functional studies suggest that mesangial cells regulate filtration rate in both a static and dynamic fashion. Mesangial excitability enables a homeostatic intraglomerular stretch reflex that integrates an increase in filtration pressure with a reduction in capillary surface area. In addition, mesangial tone is regulated by diverse vasoactive hormones. Agonists, such as angiotensin II, contract mesangial cells through a signal transduction pathway that releases intracellular stores of Ca2+, which subsequently activate nonselective cation channels and Cl- channels to depolarize the plasma membrane. The change in membrane potential activates voltage-gated Ca2+ channels, allowing Ca2+ cell entry and further activation of depolarizing conductances. Contraction and entry of cell Ca2+ are inhibited only when Ca2+-activated K+ channels (BK(Ca)) are activated and the membrane is hyperpolarized toward the K+ equilibrium potential. The mesangial BK(Ca) is a weak regulator of contraction in unstimulated cells; however, the gain of the feedback is increased by atrial natriuretic peptide, nitric oxide, and the second messenger cGMP, which activates protein kinase G and decreases both the voltage and Ca2+ activation thresholds of BK(Ca) independent of sensitivity. This enables BK(Ca) to more effectively counter membrane depolarization and voltage-gated Ca2+ influx. After hyperpolarizing the membrane, BK(Ca) rapidly inactivates because of dephosphorylation by protein phosphatase 2A. Regulation of ion channels has been linked casually to hyperfiltration during early stages of diabetes mellitus. Determining the signaling pathways controlling the electrophysiology of glomerular mesangial cells is important for understanding how glomerular filtration rate is regulated in health and disease.

Atrial natriuretic peptide inhibits endothelin-1-induced activation of JNK in glomerular mesangial cells

Atrial natriuretic peptide (ANP) has been shown to counteract various actions of endothelin-1 (ET-1) in mesangial cells. We have reported that both extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK) are activated by ET-1 and ET-1-induced activation of ERK is inhibited by ANP. To further clarify the action of ANP, we examined the effect of ANP on ET-1-induced activation of JNK. ANP inhibited ET-1-induced activation of JNK in a dose-dependent manner. This inhibitory effect of ANP was reversed by HS-142-1, an antagonist for biological receptors of ANP, while C-ANP, an analog specific to clearance receptors of ANP, failed to inhibit ET-1-induced activation of JNK. 8-Bromo-cGMP and sodium nitroprusside were also able to inhibit ET-1-induced activation of JNK, suggesting cGMP-dependent action of ANP. In contrast, ANP failed to inhibit interleukin-1 beta (IL-1 beta)-induced activation of JNK. Since an increase in intracellular calcium ([Ca2+]i) was shown to be necessary for ET-1-induced activation of JNK in mesangial cells, we measured [Ca2+]i using fura-2. ANP attenuated the ET-1-induced increase in [Ca2+]i in concentrations enough to inhibit ET-1-induced activation of JNK. Finally, ANP was able to inhibit ET-1-, but not IL-1 beta-induced increase in DNA-binding activity of AP-1 by gel shift assay. These results indicate that ANP is able to inhibit ET-1-induced activation of AP-1 by inhibiting both ERK and JNK, suggesting that ANP might be able to counteract the expression of AP-1-dependent genes induced by ET-1.

Antioxidant inhibition of protein kinase C-signaled increases in transforming growth factor-beta in mesangial cells

Protein kinase C (PKC)-signaled increases in transforming growth factor beta (TGF beta) have been implicated in the stimulation of matrix protein synthesis induced by high concentrations of glucose, thromboxane, angiotension II (AII), and other stimuli in cultured glomerular mesangial cells. In the present study, the effects of several antioxidants on mesangial cell responses to high glucose, thromboxane, and AII were examined. alpha-Tocopherol blocked increases in PKC, TGF beta bioactivity, collagen, and/or fibronectin synthesis induced in mesangial cells by high glucose, the thromboxane analog U46619, and AII. By contrast, alpha-tocopherol did not alter increases in matrix protein synthesis in mesangial cells in response to exogenous TGF beta, a cytokine that does not activate PKC in mesangial cells and whose actions to stimulate matrix protein synthesis in these cells are not blocked by PKC inhibition or downregulation. Taurine and N-acetylcystein similarly inhibited activation of PKC and increases in TGF beta in response to high glucose, U46619, and AII. alpha-Tocopherol but not taurine or N-acetylcysteine partially blocked increases in PKC activity in mesangial cells in response to the diacylglycerol (DAG) analog, phorbol dibutyrate (PDBu). Thus, alpha-tocopherol may have direct effects on interaction of the PKC system of mesangial cells with DAG that are not shared by N-acetylcysteine or taurine. Increases in TGF beta have been implicated in the pathogenesis of glomerulosclerosis in diabetes and other nephropathies. The capacity of antioxidants to block increases in TGF beta in mesangial cells in response to high glucose, thromboxane, and All suggests their potential therapeutic utility to attenuate glomerulosclerosis.

Enhanced synthesis of proteoglycans by vascular endothelial cells treated with phorbol ester

We investigated the biosynthesis of proteoglycans (PG) in endothelial cells following their treatment with phorbol 12-myristate 13-acetate (PMA). Confluent cultures of bovine aortic endothelial cells were incubated in the presence and absence of PMA (100 ng/ml) and then pulsed with [35S]sulfate, [3H]glucosamine, or [35S]sulfate plus [3H]leucine for varying times in the absence of PMA. Alternatively, confluent endothelial cells were simultaneously incubated with PMA and [35S]sulfate for varying times. The metabolically labeled PG in the cell layer and medium were analyzed. Both short-term and prolonged exposure of endothelial cells to PMA significantly stimulated PG synthesis, regardless of the experimental conditions. [35S]sulfate incorporation into newly synthesized PG in PMA-treated cells also increased by 1.7-fold and 3.6-fold over control cells, following a 15-min and 30-min pulse, respectively. Cycloheximide markedly inhibited the increased synthesis of PG in PMA-treated cells, while actinomycin D produced a moderate inhibition. PG secretion was increased in PMA-treated cells compared with control cells, while there was no significant difference in PG degradation between the two cultures. PG from control and PMA-treated endothelial cell cultures did not differ in composition or hydrodynamic sizes. The incorporation of [3H]leucine into total cellular proteins decreased significantly following exposure of endothelial cells to PMA. Endothelial cells exposed to PMA for 3 h had significantly more protein kinase C (PKC) activity than did control cells. Inhibition of PKC by calphostin C abolished the PMA-mediated stimulation of PG synthesis in endothelial cells. The results indicate that PMA stimulates PG synthesis in endothelial cells either directly or indirectly through a PKC dependent mechanism.

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.

Endothelin-1 induces loss of proteoglycans and enhances fibronectin and collagen production in cultured rabbit synovial cells

Endothelin-1 exerts a wide range of biological actions besides its characteristic vasoconstrictor function. The potential participation of endothelin-1 in rheumatic diseases has hardly been explored. We have studied the possible role of endothelin-1 as a modulator of extracellular matrix turnover in cultured rabbit synoviocytes. In relation to basal levels, endothelin-1 increased the mRNA levels of collagen I and fibronectin at 24 h (130 +/- 9% and 132 +/- 18%, respectively), but did not modify the expression of decorin core proteoglycan. Endothelin-1 also decreased proteoglycan metabolism (about 50% of proteoglycan synthesis inhibition and 270 +/- 32% of degradation rate vs. basal, P < 0.05 in both cases) and enhanced total collagen (1.5 +/- 0.5 vs. 0.8 +/- 0.2 microgram hydroxyproline/microgram DNA in basal, P < 0.05) and fibronectin protein synthesis (157 +/- 14% of [35S] methionine incorporation vs. basal, P < 0.05). The endothelin ETA receptor antagonist BQ-123 (Cyclo D-trp-D-asp-pro-D-val-leu) displaced [125I]endothelin-1 binding and inhibited endothelin-1 effects on extracellular matrix components. The cell incubation with indomethacin totally reversed the endothelin-1 effect. These data suggest that endothelin-1 may be an important mediator of the pathogenesis of joint damage, disturbing the extracellular synovial matrix turnover through the endothelin ETA receptors.

Atrial natriuretic peptide induces the expression of MKP-1, a mitogen-activated protein kinase phosphatase, in glomerular mesangial cells

Atrial natriuretic peptide (ANP) has been shown to inhibit the proliferation of various types of cells including glomerular mesangial cells. The activation of mitogen-activated protein kinase (MAPK) is one of the main signal transduction systems leading to cell proliferation. MAPK is tightly regulated by the activating kinase, MEK, and specific phosphatase MKP-1. Constitutive expression of MKP-1 has been shown to inhibit cell proliferation by suppressing MAPK activity. In order to understand the mechanism of the anti-proliferative effect of ANP, we examined whether ANP could inhibit MAPK by inducing MKP-1 in cultured rat glomerular mesangial cells. ANP increased the expression of MKP-1 mRNA in a dose-dependent (10 nM maximum) and time-dependent, with a peak stimulation at 30 min, manner. Receptor for ANP is a transmembrane guanylyl cyclase. Activation of guanylyl cyclase of ANP receptor by ligand plays an essential role in ANP signal transduction. 8-Bromo-cGMP, a cell permeable analogue of cyclic GMP, and sodium nitroprusside, an activator of soluble guanylyl cyclase, could mimic the effects of ANP and were able to induce the expression of MKP-1 in a similar time course as ANP. The protein expression of MKP-1 was maximally stimulated by ANP at 120 min. Treatment of the cells with ANP for 120 min resulted in an inhibition of phorbol ester-induced activation of MAPK, while the activation of MEK was not affected by ANP. These results indicate that ANP might inhibit the proliferation of mesangial cells by inactivating MAPK through the induction of MKP-1.

Protein kinase C in diabetic nephropathy

Protein kinase C is activated in numerous tissues obtained from diabetic animals and in several cultured cell systems exposed to high media glucose in vitro including glomerular mesangial cells. Several activators of protein kinase C, such as high media glucose, angiotensin II, phorbol ester, low density lipoprotein, and the thromboxane analogue U-46619, increase TGF beta bioactivity or mRNA expression and increase the synthesis of extracellular matrix proteins by mesangial cells in culture. The studies described in the present report support the hypothesis that activation of protein kinase C by thromboxane, an eicosanoid whose production is known to be elevated in diabetes, increases TGF beta production by mesangial cells in culture. TGF beta then acts to increase extracellular matrix protein synthesis through a mechanism that does not require active protein kinase C. Thus, activation of protein kinase C in the glomerulus in diabetes could contribute to mesangial expansion by stimulating active TGF beta production.

Protein kinase C signals thromboxane induced increases in fibronectin synthesis and TGF-beta bioactivity in mesangial cells

Previous studies have demonstrated that thromboxane (TX) stimulates matrix protein synthesis in mesangial cells (MC), and that this action is signalled by receptor mediated activation of protein kinase C (PKC). In the present study, we examined the hypothesis that activation of PKC by TX signals increases in transforming growth factor beta (TGF-beta) bioactivity, which in turn induces enhanced matrix protein synthesis. In cultured rat MC, the TXA2/prostaglandin endoperoxide analogue U-46619, but not exogenous human platelet TGF-beta 1, activated PKC as reflected by enhanced in situ phosphorylation of MARCKS protein, an endogenous substrate of PKC. U-46619 and TGF-beta 1 stimulated fibronectin (Fn) synthesis in MC, as shown by [35S]methionine incorporation into immunoprecipitable Fn. Pan-specific rabbit anti-TGF-beta antibody blocked the increases in Fn synthesis induced by exogenous TGF-beta and those induced by U-46619 at 24 to 72 hours after addition. Anti-TGF-beta antibody did not block the small increases in FN synthesis observed six hours after addition of U-46619, suggesting that this acute response was not dependent on TGF-beta. Anti-TGF-beta antibody also failed to block activation of PKC by U-46619. U-46619 and 50 nM of the PKC agonist phorbol dibutyrate (PDBu) significantly increased both the active fraction and total (latent plus active) TGF-beta in MC culture media, as assayed with the mink lung epithelial cell bioassay system.(ABSTRACT TRUNCATED AT 250 WORDS)

Impaired nitric oxide release by glomeruli from diabetic rats

Basal nitric oxide (NO) production and NO responses to carbamylcholine (CCh) and the Ca2+ ionophore A23187 were measured with a NO electrode in glomeruli isolated from 2 to 3-month-diabetic versus age-matched control rats. In the presence of CCh or A23187, NO production was markedly reduced in glomeruli from diabetic versus control rats. Spontaneous generation of NO by s-nitrosopenicillamine (SNAP) was also reduced in the presence of glomeruli from diabetic rats as compared with values either in control glomeruli or in buffer alone. The results demonstrate an impairment of NO generation and/or stability in glomeruli from 2 to 3-month-diabetic rats, which correlates with the previously observed suppression of NO-dependent glomerular cyclic guanosine 3',5'-monophosphate (cGMP) induced by diabetes.