PubMed Health⌕ Search

Biomedical subjects

M Ashraf

Publications and source records attributed to M Ashraf.

At least 55 records · Page 3Linked to original sources
PubMed1998

Activation of alpha1-adrenergic receptor during Ca2+ pre-conditioning elicits strong protection against Ca2+ overload injury via protein kinase C signaling pathway.

The objective was to test the hypothesis that transient activation of the alpha1-adrenergic receptor mimics the beneficial effects of Ca2+ preconditioning on the Ca2+ paradox (Ca2+ PD) injury in rat hearts, and that the protection is mediated by protein kinase C (PKC) signaling pathway. Langendorff-perfused rat hearts were subjected to the Ca2+ PD (10 min of Ca2+ depletion followed by 10 min of Ca2+ repletion). The effects of alpha1-adrenergic receptor activation and other interventions on functional, biochemical and pathological changes were assessed. In hearts pretreated with 50 micromol/l phenylephrine, left ventricular end-diastolic pressure and coronary flow were significantly preserved after Ca2+ PD; furthermore, peak loss of lactate dehydrogenase was significantly decreased while ATP was significantly preserved. A remarkable preservation of cell structure was observed in phenylephrine-treated hearts in contrast to non-treated Ca2+ PD hearts. However, pre-conditioning elicited by phenylephrine caused only a mild improvement in left ventricular developed pressure (LVDP) as opposed to its impressive recovery of left ventricular end-diastolic pressure (LVEDP), heart rate (HR), or coronary flow (CF). The salutary effects of phenylephrine on the Ca2+ PD injury were almost similar to those observed in hearts which underwent Ca2+ pre-conditioning (CPC) or were pretreated with 1-stearoyl-2-arachidonoyl-glycerol (SAG), a potent PKC activator. In phenylephrine pretreated hearts, PKC isoform-alpha was localized in the sarcolemma and nucleus, while PKC-delta and PKC-epsilon were localized in the cell membrane, and intercalated disk respectively. Prazosin, a specific alpha1-adrenergic receptor antagonist completely abolished the beneficial effects of phenylephrine on the Ca2+ PD and blocked translocation of PKC isoforms. In addition, prazosin (1 micromol/l) also reversed salutary effects of CPC. Moreover, the beta-adrenergic antagonist, propranolol, had no effect on the protection provided by phenylephrine against the Ca2+ PD injury. This study suggests that the activation of the alpha1-adrenergic receptor confers protection against the lethal injury of the Ca2+ PD via PKC-mediated signaling pathways. The protection is shared by stimuli common with calcium pre-conditioning.

Animals↗
PubMed1998

Oxidant stress with hydrogen peroxide attenuates calcium paradox injury: role of protein kinase C and ATP-sensitive potassium channel.

OBJECTIVE: We tested the hypotheses that low concentration of H2O2 attenuates the Ca2+ paradox (Ca2+ PD) injury, and that activation of protein kinase C (PKC) and/or ATP-sensitive potassium channel (KATP) are involved in the protective effects of H2O2. METHODS: Langendorff-perfused rat hearts were subjected to the Ca2+ PD (10 min of Ca2+ depletion followed by 10 min of Ca2+ repletion). Functional and biochemical effects of H2O2 and other interventions on the cell injury induced by the Ca2+ PD were assessed. RESULTS: In the Ca2+ PD hearts pretreated with 20 mumol/l H2O2, left ventricular end-diastolic pressure and coronary flow were significantly preserved. Furthermore, peak lactate dehydrogenase release was significantly decreased and ATP contents were more preserved, compared with non-treated Ca2+ PD hearts. H2O2-treated hearts also showed remarkable preservation of cell structure. Addition of a specific PKC inhibitor, chelerythrine during H2O2 treatment completely abolished the beneficial effects of H2O2 on the Ca2+ PD. Similarly, an activator of PKC. Phorbol 12-myristate 13 acetate mimicked the protection by H2O2. Furthermore, pretreatment with a KATP opener, cromakalim also provided protection similar to H2O2 against the Ca2+ PD injury. However, a specific KATP inhibitor, glibenclamide was not able to completely block the effects of H2O2. CONCLUSIONS: These findings suggest that pretreatment with low concentration of H2O2 provides significant protection against the lethal injury of Ca2+ PD in rat hearts. PKC-mediated signaling pathways appear to play a crucial role in the protection against the Ca2+ PD injury.

Adenosine Triphosphate↗
PubMed1998

Microbial transformations of hypolipemic E-guggulsterone.

Biotransformation of E-guggulsterone (pregna-4,17(20)-cis-diene-3,16-dione) (1) by Aspergillus niger resulted in the formation of four new hydroxyl derivatives identified as 7 beta-hydroxypregna- 4,17(20)-trans-diene-3,16-dione (2), 7 beta-hydroxypregna-4,17(20)-cis-diene-3,16-dione (3), 7 beta- hydroxypregn-4-ene-3,16-dione (4), and 7 beta,15 beta-dihydroxypregn-4-ene-3,16-dione (5). The biotransformation of 1 with Cephalosporium aphidicola also resulted in the formation of four new steroidal derivatives as 11 alpha-hydroxypregna-4,17(20)-trans-diene-3,16-dione (6), 11 alpha- -hydroxypregna-4,17(20)-cis-diene-3,16-dione (7), 11 alpha,15 beta-dihydroxypregna-4,17(20)-trans-diene- 3,16-dione (8), and 11 alpha,15 beta-dihydroxypregna-4,17(20)-cis-diene-3,16-dione (9). The structures of these compounds were elucidated on the basis of 1D and 2D NMR spectroscopic techniques.

Anti-Bacterial Agents↗
PubMed1998

Holmium: YAG lasertripsy for ureteric calculi: an experience of 300 procedures.

OBJECTIVE: To assess the success of holmium:YAG lasertripsy in the management of ureteric calculi and to audit the complications of the procedure, with special reference to strictures in the ureter. PATIENTS AND METHODS: A total of 300 ureteroscopic laser procedures were carried out on 265 patients (204 male and 61 female, median age 51 years, range 2-95) with ureteric calculi. At ureteroscopy, the calculi were present in the upper ureter in 44%, mid-ureter in 37% and lower ureter in 19% of patients; most calculi were > 5 mm. A 7.5 F Wolf semi-rigid ureteroscope was used and the holmium:YAG laser energy delivered using the Sharplan ML210 device at 0.8-1.0 J/pulse. The patients were followed up at approximately 6 weeks with limited intravenous urography or ultrasonography to assess clearance and the incidence of strictures. RESULTS: Stones were completely cleared in 90% of the patients, with the best results in the lower and mid-ureter (97% and 96%, respectively) followed by the upper ureter (89%). Alternative procedures were required in only 17 (7%) patients; extracorporeal shock-wave lithotripsy in 13, percutaneous nephrolithotomy in two and open pyelolithotomy in two patients. Complications with ureteric perforation in 11 patients, including laparotomy for peritonitis in one, serious sepsis in two and strictures in 10 patients. Strictures were more common in association with impacted calculi in the upper ureter early in the series. CONCLUSIONS: Holmium:YAG lasertripsy is a highly effective treatment for ureteric calculi, with strictures related to the treatment of difficult upper ureteric calculi.

Adolescent↗
PubMed1998

Metabolic effects of low cortisol during exercise in humans.

This study examined the physiological effect of reduced plasma cortisol (C) during prolonged exercise in humans. The effects of normal C (NC) were compared with metyrapone-induced low C (LC) on plasma substrate availability and the respiratory exchange ratio during 2 h of exercise at approximately 60% peak O2 consumption in nine subjects. The C responses were compared with preexercise (Pre) levels and with a rest day (Con). At rest, C was attenuated by approximately 70% for LC compared with NC. At rest, plasma glucose, lactate, glycerol, beta-hydroxybutyrate, alanine, branched-chain amino acids, insulin, glucagon, growth hormone, epinephrine, and norepinephrine were similar under LC and NC (P > 0.05). During exercise under NC, plasma C increased compared with Pre, whereas it remained unchanged during LC. During NC, plasma C was elevated at 90 min (compared with Con) and at 120 min (compared with Con and Pre). During exercise, plasma glucose decreased to the same extent and lactate was similar under both conditions, whereas plasma glycerol, beta-hydroxybutyrate, alanine, and branched-chain amino acids were higher (P < 0.01) under NC. Plasma insulin declined (P = 0.01) to a greater extent under LC, whereas growth hormone, epinephrine, and norepinephrine tended to be higher (0.05 </= P </= 0.10). Plasma glucagon increased under both conditions (P < 0.01). The respiratory exchange ratio did not differ between conditions. We conclude that, during exercise, 1) C accelerates lipolysis, ketogenesis, and proteolysis; 2) under LC, glucoregulatory hormone adjustments maintain glucose homeostasis; and 3) LC does not alter whole body substrate utilization or the ability to complete 2 h of moderate exercise.

Adult↗
PubMed1998

Identification of formulation and manufacturing variables that influence in vitro dissolution and in vivo bioavailability of propranolol hydrochloride tablets.

The purpose of this study was to evaluate the effect of formulation and processing changes on the dissolution and bioavailability of propranolol hydrochloride tablets. Directly compressed blends of 6 kg (20,000 units) were prepared by mixing in a 16-qt V blender and tablets were compressed on an instrumented Manesty D3B tablet press. A half-factorial (2(5-1), Resolution V) design was used to study the following variables: filler ratio (lactose/dicalcium phosphate), sodium starch glycolate level, magnesium stearate level, lubricant blend time, and compression force. The levels and ranges of the excipients and processing changes studied represented level 2 or greater changes as indicated by the Scale-up and Post Approval Changes (SUPAC-IR) Guidance. Changes in filler ratio, disintegrant level, and compression force were significant in affecting percent drug released (Q) in 5 min (Q5) and Q10. However, changes in magnesium stearate level and lubricant blend time did not influence Q5 and Q10. Hardness was found to be affected by changes in all of the variables studied. Some interaction effects between the variables studied were also found to be significant. To examine the impact of formulation and processing variables on in vivo absorption, three batches were selected for a bioavailability study based on their dissolution profiles. Thirteen subjects received four propranolol treatments (slow-, medium-, and fast-dissolving formulations and Inderal 80 mg) separated by 1 week washout according to a randomized crossover design. The formulations were found to be bioequivalent with respect to the log Cmax and log AUC0-infinity. The results of this study suggest that (i) bioavailability/bioequivalency studies may not be necessary for propranolol and perhaps other class 1 drugs after level 2 type changes, and (ii) in vitro dissolution tests may be used to show bioequivalence of propranolol formulations with processing or formulation changes within the specified level 2 ranges examined.

Adrenergic beta-Antagonists↗
PubMed1997

Morphological features of the retinal pigment epithelium in the toad, Bufo marinus.

BACKGROUND: The toad's (Bufo marinus) retinal pigment epithelium (RPE) has been used in many studies as a model for understanding its role and interaction with the neural retina (NR). In this study, the fine structure of the RPE is described. METHODS: In vitro RPE-chorion preparations from the toad were studied after separation from the NR. Tissues were processed for light and electron microscopy. RESULTS: The RPE consists of a single layer of cells joined by a series of tight junctions forming part of the blood-retina barrier. These cells had minimal infolding of the basal membrane and numerous microvillous processes extending from the apical surface and surrounding photoreceptor outer segments. Internally, RPE cells display a large nucleus, numerous mitochondria located at the basal membrane, extensive smooth endoplasmic reticulum, myeloid bodies, phagosomes, scattered polysomes, large lipid droplets and melanin granules. Rough endoplasmic reticulum is relatively scarce within these cells. The choriocapillaris consists of large blood vessels facing Bruch's membrane. Bruch's membrane is typical of other vertebrates, being pentalaminate over the whole retina. The endothelium of the choriocapillaris facing Bruch's membrane is typically very thin but shows few fenestrations. CONCLUSIONS: Due to the ultrastructural similarities of toad RPE with that of mammals, it can serve as an excellent model for the study of retinal detachment/reattachment and their cellular and molecular mechanisms.

Adaptation, Ocular↗
PubMed1997

Swimming training lowers the resting blood pressure in individuals with hypertension.

BACKGROUND: Despite the fact that swimming is often recommended for the prevention and treatment of hypertension, no study has examined the potential efficacy of regular swimming exercise for lowering the blood pressure in hypertensive humans. OBJECTIVE: To test the hypothesis that regular swimming exercise lowers the resting blood pressure. DESIGN: A 10-week closely supervised swimming training program compared with a non-exercising control group. PATIENTS: Eighteen previously sedentary men and women [aged 48 +/- 2 years (mean +/- SEM)] with stage 1 or 2 essential hypertension. RESULTS: The resting heart rated, an index of cardiovascular adaptation, decreased in the swimming training group from 81 +/- 4 to 71 +/- 3 beats/min (P < 0.01). The body mass and body fat percentage did not show statistically significant changes. The systolic blood pressure of patients in the seated position fell significantly (P < 0.05) from 150 +/- 5 to 144 +/- 4 mmHg. The seated diastolic blood pressure did not change significantly. A similar magnitude of reductions in systolic blood pressure (P < 0.05) was also found in patients in the supine position. No significant changes in plasma catecholamine concentrations, casual forearm vascular resistance, plasma volume and blood volume were observed. There were no significant changes in any of these variables in the control group. CONCLUSION: Swimming training elicits significant reductions in arterial blood pressure at rest in individuals with hypertension. This is a clinically important finding since swimming can be a highly useful alternative to land-based exercises for hypertensive patients with obesity, exercise-induced asthma, or orthopedic injuries.

Blood Flow Velocity↗
PubMed1997

Isoproterenol mimics calcium preconditioning-induced protection against ischemia.

We tested the hypothesis that a transient increase in intracellular calcium concentration ([Ca2+]i) before prolonged ischemia triggers the activation of protein kinase C (PKC), resulting in significant protection against ischemic injury. Ca2+ preconditioning (3 cycles of 1-min Ca2+ depletion and 5-min Ca2+ repletion) and pharmacological intervention with isoproterenol (Iso) were employed to increase the Ca2+ influx. Langendorff-perfused rat hearts were subjected to 40 min of global ischemia followed by 30 min of reperfusion (I/R). A significant functional recovery and minimal biochemical changes were observed in Ca2+-preconditioned hearts after I/R. Pretreatment with 0.1 micromol/l Iso caused a sudden increase in left ventricular contractility, a significant decrease in lactate dehydrogenase release, preservation of ATP content, and left ventricular function compared with nontreated I/R hearts. Administration of verapamil during Iso treatment blunted the salutary effects of Iso on I/R and pretreatment with BAY K 8644, an L-type Ca2+-channel opener, mimicked Iso-induced protection. Addition of propranolol or specific PKC inhibitors (chelerythrine or bisindolylmaleimide) during Iso infusion completely abolished the beneficial effects of Iso. These results demonstrate that 1) treatment with a low dose of Iso provides significant protection against ischemic injury, 2) transient elevation of [Ca2+]i is a strong activator of PKC, and 3) PKC plays a crucial role in the subcellular mechanisms of protection by activating second messenger signals during Iso-induced preconditioning.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1997

Ca2+ as a mediator of ischemic preconditioning.

We tested the hypothesis that elevation of [Ca2+]i during ischemic preconditioning (IPC) stimulates protein kinase C (PKC), which confers the protection against the ischemic injury. Langendorff-perfused rat hearts were subjected to 40-minute global ischemia followed by 30-minute reperfusion (I/R). In preconditioned groups, hearts were subjected to either IPC, consisting of 5-minute global ischemia and 10-minute reperfusion, or high-Ca2+ preconditioning (HCPC), ie, the 5-minute perfusion of higher Ca2+ perfusate (2.3 mmol/L Ca2+) followed by 10-minute perfusion of normal perfusate (1.8 mmol/L Ca2+), and then were subjected to I/R. A significant functional recovery and decreased lactate dehydrogenase release were observed in HCPC and IPC hearts compared with ischemic control hearts. ATP contents of preconditioned hearts were significantly higher than those of the ischemic control hearts. The cell structure in preconditioned hearts was preserved better than that in the ischemic control hearts. Furthermore, the activation and translocation of PKC from cytoplasm to sarcolemma were observed in the preconditioned hearts. Verapamil administered during IPC significantly attenuated the salutary effects of IPC. Administration of chelerythrine, a specific PKC inhibitor, completely abolished the HCPC- and IPC-induced cardioprotection. The translocation of PKC by IPC was blocked by verapamil or chelerythrine. Immunohistochemical study using rabbit polyclonal antibody against PKC isoforms indicated that stress induced by IPC or HCPC evoked the translocation of PKC alpha and PKC delta to the cell membrane. Translocation of PKC isoforms was attenuated by the treatment with verapamil or chelerythrine. These results demonstrate that (1) a transient increase in [Ca2+]i during IPC is an important trigger for the activation of PKC, which is responsible for cardioprotection; (2) the elevation of [Ca2+]i during IPC, at least partly, resulted from Ca2+ entry via voltage-dependent Ca2+ channel; and (3) activation and translocation of PKC alpha and PKC delta occur during IPC and HCPC and may be important in preconditioning.

Adenosine Triphosphate↗
PubMed1997

Growth of trypanosomes in vivo, host body weight gains, and food consumption in zinc-deficient mice.

This study examined the effect of zinc deficiency on food consumption and the growth of mice infected with Trypanosoma musculi or immunized with parasite products. In addition, the effects of zinc deficiency on the growth and development of parasites in vivo was studied. Infected mice consumed more food than noninfected mice, and the level of food consumption in the zinc-deficient mice was much less and showed general decline during the observation period. Also, infected mice on both full-complement and zinc-deficient diets gained more body weight than control mice. Throughout the observational period, trypanosomes from zinc-deficient mice showed considerably higher variability in size as determined by coefficient of variation. In both dietary groups, the average length of trypanosomes was not significantly different.

Animals↗
PubMed1997

Hepatic cells' mitotic and peritoneal macrophage phagocytic activities during Trypanosoma musculi infection in zinc-deficient mice.

The effects of zinc deficiency on hepatic cell mitotic and peritoneal macrophage phagocytic activities were examined in mice infected with Trypanosoma musculi or immunized with parasitic products. On a full-complement or pair-fed diet, infected and homogenate-inoculated mice showed mitotic activity gains of 7.9% to 80.3% and 6.5% to 99.0%, respectively. Infected and homogenate-inoculated mice on a zinc-deficient diet showed 21.8% to 95.7% and 17.2% to 65.2%, respectively, more dividing liver cells compared with controls. In comparison to controls, macrophages isolated from infected and homogenate-immunized mice on full-complement or pair-fed diets had phagocytized 13.4% to 31.4% more latex particles from day 50 to 80. In the zinc-deficient group, macrophages isolated from infected mice had significant numbers of phagocytized latex particles (1.8% to 38.5%) from day 20 to day 80 compared with controls. The homogenate-immunized mice also had increased numbers (18.6 to 30.8%) of phagocytized latex particles.

Animals↗
PubMed1996

Cross-linking of the high-affinity IgE receptor induces the expression of cyclo-oxygenase 2 and attendant prostaglandin generation requiring interleukin 10 and interleukin 1 beta in mouse cultured mast cells.

When mouse bone marrow-derived mast cells (BMMC) developed in interleukin (IL)-3 were activated with IgE and antigen (IgE/antigen) in the presence of both IL-10 and IL-1 beta, two sequential phases of prostaglandin (PG)D2 generation were elicited, in which the first phase occurred by 1 h and the second phase from 2 to 10 h. The delayed phase of PGD2 generation was accompanied by a marked induction of cyclo-oxygenase (COX)-2 mRNA, which reached a peak at 1-2 h, followed by that of its protein from 2-10 h, with a peak at 5 h. The immediate phase of PGD2 generation was completely abrogated by the irreversible inhibition of pre-existing COX-1 by aspirin pretreatment, whereas the delayed phase of PGD2 generation was almost undetectable in the presence of the COX-2 inhibitor NS-398. A detailed analysis of the individual effects of IgE/antigen, IL-10 and IL-1 beta on COX-2 expression revealed that IgE/antigen and IL-10 each initiated and stabilized COX-2 mRNA expression, leading to an increase in the expression of its protein. Conversely, IL-1 beta stabilized the COX-2 protein without affecting its mRNA level. The induction of COX-2 by IgE/antigen with IL-10 and IL-1 beta preceded the induction of transcripts for endogenous cytokines such as IL-6, IL-1 beta and IL-10. The inhibition of PGD2 generation by indomethacin did not affect the induction of COX-2 or these cytokines. Thus the two major delayed-phase responses of BMMC after IgE-dependent activation, namely COX-2-dependent PGD2 generation and cytokine production, are regulated independently.

Animals↗
PubMed1996

Late ischemic preconditioning is mediated in myocytes by enhanced endogenous antioxidant activity stimulated by oxygen-derived free radicals.

The primary objective of the study was to test the hypothesis that oxygen radical during initial anoxia stimulate endogenous antioxidant activity in late preconditioning in myocytes. Isolated rat myocytes were preconditioned in one group with two cycles of 5 minutes of anoxia and 5 minutes of reoxygenation and in another group with exogenous superoxide anion (.O2-) generated by reaction of xanthine oxidase with xanthine. Myocytes were kept for 24 hours, after which they were exposed to 60 minutes of anoxia and 60 minutes of reoxygenation. Preconditioned myocytes exhibited decreased LDH release, reduced malondialdehyde formation, increased cell viability, and well-preserved cell structure. .O2- production was increased in myocytes immediately after treatment with repetitive anoxia (1.65 +/- 0.08 nmol/mg protein) or exogenous .O2- (1.42 +/- 0.11 nmol/mg protein). Allopurinol, a xanthine oxidase inhibitor, abolished .O2- production during the initial preconditioning period. Twenty-four hours later, Mn SOD activity declined in anoxic control myocytes (0.38 +/- 0.06 U/mg protein), whereas it increased significantly in myocytes preconditioned with repetitive anoxia (3.25 +/- 0.15 nmol/mg protein) or with exogenous .O2- (2.27 +/- 0.10 nmol/mg protein). The increase in Mn SOD activity and myocardial protective effects observed in preconditioned myocytes were totally blocked by allopurinol. These results indicate that oxygen radicals generated during the initial preconditioning period activate endogenous antioxidant defense (increased Mn SOD activity) 24 hours later, which contributes to the late cardioprotection of preconditioning.

Animals↗
PubMed1996

Direct evidence that initial oxidative stress triggered by preconditioning contributes to second window of protection by endogenous antioxidant enzyme in myocytes.

BACKGROUND: We tested the hypothesis that late preconditioning is associated with increased antioxidant enzyme activity induced by initial oxidative stress. METHODS AND RESULTS: Isolated rat myocytes were preconditioned either with two cycles of 5 minutes of anoxia and 5 minutes of reoxygenation or with exogenous superoxide anion (O2-) generated by reaction of xanthine oxidase with xanthine. Myocytes were allowed to recover for 60 minutes or 24 hours, after which they were subjected to 60 minutes of anoxia and 60 minutes of reoxygenation. After 60 minutes or 24 hours, the protection was evidenced by decreased O2- production, increased Mn superoxide dismutase (Mn-SOD) activity, increased call viability, decreased LDH release, reduced malondialdehyde formation, high-energy phosphate preservation, and improved call morphology in preconditioned and O2(-)-treated myocytes. Immediately after treatment with O2- or repetitive, brief anoxia, O2- production was increased in myocytes. Longer anoxia resulted in loss of Mn-SOD activity in anoxic controls 24 hours later, whereas it was significantly increased in preconditioned and O2- -treated myocytes. O2- production was inhibited in preconditioned and O2(-)-myocytes. Myocytes treated with Mn-SOD during short, intermittent anoxia exhibited decreased activity of Mn-SOD and increased O2- production 24 hours later. Mn-SOD activity in late preconditioning was considerably higher than that in classic preconditioning. CONCLUSIONS: These results suggest that a burst of oxygen free radicals generated during the initial periods of brief, repetitive anoxia increases myocardial antioxidant activity 24 hours later and that it contributes to the late cardioprotective effect of preconditioning.

Adenosine Triphosphate↗
PubMed1996

Case report: strongyloidiasis refractory to treatment with ivermectin.

Strongyloides stercoralis usually causes chronic asymptomatic infection in humans. However, in patients with AIDS, malignancy, and individuals receiving corticosteroids, disseminated infection can develop, associated with an extremely high mortality rate and frequent treatment failure with thiabendazole. Recently, ivermectin was found to be very effective in such patients. The authors report a case of strongyloidiasis in a patient with hypogammaglobulinemia in which ivermectin failed to clear Strongyloides larvae from stool, despite repeated courses of treatment throughout 14 months.

Adult↗
PubMed1996

Preconditioning of bovine endothelial cells. The protective effect is mediated by an adenosine A2 receptor through a protein kinase C signaling pathway.

We tested the hypothesis that anoxic preconditioning could protect coronary endothelial cells against anoxic and reoxygenation injury and that this preconditioning effect could be mediated by an adenosine A2 receptor via the protein kinase C (PKC) pathway. Cells were preconditioned with 10-minute anoxia and 10-minute reoxygenation and were then subjected to anoxia for 60 minutes, followed by 120 minutes of reoxygenation. In some groups, the preconditioning effect was prevented by 8-sulfophenyltheophylline (SPT [50 mumol/L], a nonselective adenosine receptor antagonist), or calphostin C (100 nmol/L, a PKC inhibitor). In other groups, 2-p-(2-carboxyethyl)phenethylamino-5'N-ethylcarboxyamido- adenosine (CGS-21680 [20 nmol/L], an adenosine A2 receptor agonist, R-(--)-N6-(2-phenylisopropyl)-adenosine (R-PIA [50 nmol/L], an adenosine A1 receptor agonist), or 4 beta-phorbol 12-myristate 13-acetate (PMA [100 nmol/L], a PKC activator) was given as a pretreatment to mimic the preconditioning effect. Endothelial cells were also pretreated with 100 nmol/L calphostin C to confirm whether inhibition of PKC can block the effects of adenosine A2 receptor activation by CGS-21680 on anoxia and reoxygenation injury. Preconditioning reduced LDH release, increased adenosine release, promoted translocation of PKC from cytosol to membrane, increased cell viability, and preserved ATP content and cell morphology. Pretreatment with either CGS-21680 or PMA resulted in protection similar to that seen with anoxic preconditioning. The protection was totally abolished by SPT or calphostin C. The results suggest that (1) preconditioning protects coronary endothelial cells against anoxia and reoxygenation injury, (2) the protection is probably mediated by activation of adenosine A2 receptors through the PKC pathway, and (3) the preservation of endothelial cells may be one of the mechanisms of myocardial preconditioning.

Adenosine↗