Pathophysiological actions of protease activated receptors (PARs).

Serine proteases such as thrombin, mast cell tryptase, trypsin, or cathepsin G, for example, are highly active mediators with diverse biological activities. So far, proteases have been considered to act primarily as degradative enzymes in the extracellular space. However, their biological actions in tissues and cells suggest important roles as a part of the body's hormonal communication system during inflammation and immune response. These effects can be attributed to the activation of a new subfamily of G protein-coupled receptors, termed protease-activated receptors (PARs). Four members of the PAR family have been cloned so far. Thus, certain proteases act as signaling molecules that specifically regulate cells by activating PARs. After stimulation, PARs couple to various G proteins and activate signal transduction pathways resulting in the rapid transcription of genes that are involved in inflammation. For example, PARs are widely expressed by cells involved in immune responses and inflammation, regulate endothelial-leukocyte interactions, and modulate the secretion of inflammatory mediators or neuropeptides. Together, the PAR family necessitates a paradigm shift in thinking about hormone action, to include proteases as key modulators of biological function. Novel compounds that can modulate PAR function may be potent candidates for the treatment of inflammatory or immune diseases.

Effect of coenzyme Q10 on catalase activity and other antioxidant parameters in streptozotocin-induced diabetic rats.

Although coenzyme Q10 (CoQ10) is a component of the oxidative phosphorylation process in mitochondria that converts the energy in carbohydrates and fatty acids into ATP to drive cellular machinery and synthesis, its effect in type I diabetes is not clear. We have studied the effect of 4 wk of treatment with CoQ10 (10 mg/kg, ip, daily) in streptozotocin (STZ)-induced (40 mg/kg, iv in adult rats) type I diabetes rat models. Treatment with CoQ10 produced a significant decrease in elevated levels of glucose, cholesterol, triglycerides, very-low-density lipoprotein, low-density lipoprotein, and atherogenic index and increased high-density lipoprotein cholesterol levels in diabetic rats. CoQ10 treatment significantly decreased the area under the curve over 120 min for glucose in diabetic rats, without affecting serum insulin levels and the area under the curve over 120 min for insulin in diabetic rats. CoQ10 treatment also reduced lipid peroxidation and increased antioxidant parameters like superoxide dismutase, catalase, and glutathione in the liver homogenates of diabetic rats. CoQ10 also lowered the elevated blood pressure in diabetic rats. In conclusion, CoQ10 treatment significantly improved deranged carbohydrate and lipid metabolism of experimental chemically induced diabetes in rats. The mechanism of its beneficial effect appears to be its antioxidant property.

Effect of Manilkara hexandra (Roxb.) Dubard against experimentally-induced gastric ulcers.

Effects of the flavonoid rich fraction of the stem bark of Manilkara hexandra (Roxb.) Dubard, have been studied on ethanol, ethanol-indomethacin and pylorus ligated gastric ulcers in experimental animals. Oral administration of the ethyl acetate extract (extract A3) inhibited the formation of gastric lesions induced by ethanol in a dose dependent manner. The protective effect of extract A3 against ethanol induced gastric lesions was not abolished by pretreatment with indomethacin (10 mg kg(-1)). Further, extract A3 inhibited increase in vascular permeability due to ethanol administration. Extent of lipid peroxidation was significantly reduced in animals treated with extract. Extract A3 also inhibited the formation of gastric ulcers induced by pylorus ligation, when administered both orally and intraperitoneally. Moreover, pretreatment with extract A3 increased mucus production and glycoprotein content, which was evident from the rise in mucin activity and TC: PR ratio.

Evaluation of the effects of nicorandil on experimentally induced gastric ulcers.

The present study was designed to evaluate the effects of a potassium channel opener, nicorandil, and to elucidate its possible mechanism of action in aspirin plus pylorus ligation induced and ethanol-induced gastric ulcers in rats. In an attempt to ascertain the involvement of K(ATP) channels in the modulation of gastric ulcers, the effects of nicorandil alone as well as in the presence of the K(ATP) channel blocker glibenclamide were studied. Nicorandil and glibenclamide were administered orally at a dose of 2 mg/kg throughout the study. Nicorandil showed significant protection in all the selected models that was evident from a significant reduction in the ulcer index. The results of nicorandil treatment were comparable with those of cimetidine treatment in both models. Glibenclamide was found to inhibit this effect of nicorandil. Further, glibenclamide showed proulcerogenic potential in ethanol and aspirin plus pylorus ligation models. In the aspirin plus pylorus ligation model, nicorandil showed a significant reduction in total acidity, pepsin activity, and protein content and a significant rise in mucin activity. The effect of nicorandil was also studied on gastric mucosal blood flow (GMBF). The GMBF was found to be more increased in the test group than in the control group, indicating enhancement of GMBF by nicorandil. Glibenclamide reversed this effect of nicorandil as well. It is concluded from our study that nicorandil possesses antiulcer activity in the models employed in the present study. This may be attributed to the opening of K(ATP) channels, inhibition of acid secretion, enhancement of mucin activity, and improvement in GMBF.

Antiulcer activity and the mechanism of action of magaldrate in gastric ulceration models of rat.

The present study was undertaken to investigate the mechanism of cytoprotective effects of magaldrate in aspirin plus pylorus-ligation model and ethanol-induced gastric ulcer model in rats. Magaldrate (60 mg/kg, p.o.) produced a significant reduction in the ulcer index and significant increase in mucus content in ethanol-induced gastric ulceration in rats. In aspirin plus pylorus-ligation model magaldrate produced significant decrease in ulcer index, total acidity and protein content (PR). It did not produce any significant change in volume of gastric secretion. However, it produced significant increase in total carbohydrate (TC) level but not in ratio between TC and proteins. It also produced a significant decrease in lipid peroxidation (as expressed by thiobarbituric acid reactive substance). Our data suggests the cytoprotective action of magaldrate on gastric mucosal cells which may be due to protection of gastric mucosa from lipid peroxidation.

Effect of nifedipine and enalapril on insulin-induced glucose disposal in spontaneous hypertensive and diabetic rats.

Hypertension and diabetes mellitus are associated with hyperinsulinemia and insulin resistance. The present work was undertaken to study the effects of enalapril and nifedipine on insulin sensitivity in spontaneously hypertensive (SH) rats and diabetic rats. Insulin sensitivity was measured by insulin tolerance test using K(ITT) as an index of insulin mediated glucose metabolism. The time to produce 50% fall in initial blood sugar level (T1/2) was significantly higher in non-insulin dependent diabetes mellitus (NIDDM) and SH rats as compared to Wistar control. The mean K(ITT) values were significantly lower in NIDDM and SH rats as compared to Wistar control. Treatment with nifedipine (10 mg/kg) and enalapril (5 mg/kg) for 15 days produced a significant reduction in T1/2. Further, K(ITT) value was found to be significantly increased in SH rats treated with nifedipine or enalapril as compared to control. Our data indicate that NIDDM and SH rats are not only hyperinsulinemic but also insulin resistant. Nifedipine and enalapril treatment produced increase in insulin sensitivity in these animals.

Effect of chronic treatment with amlodipine in non-insulin-dependent diabetic rats.

We have investigated the effects of amlodipine on streptozotocin-(STZ) induced neonatal non-insulin-dependent diabetes mellitus (NIDDM) rats. NIDDM was induced by intraperitoneal injection of STZ (70 mg kg-1) to 5-day-old rat pups. The animals were weaned at 30 days and maintained with food and water ad libitum for 3 months. Amlodipine (5 mg kg-1 p.o.) was administered for 6 weeks after the animals were confirmed diabetic (3 months after the STZ injection). A group of control animals were also maintained and this group received citrate buffer 5 days after birth. Fasting- and fed-glucose levels in NIDDM rats were significantly higher than control rats. Treatment with amlodipine reduced the elevated fasting- and fed-glucose levels significantly. Results of the oral glucose tolerance test (OGTT) revealed the glucose tolerance is impaired in the NIDDM rats. There was a marked increase in glucose levels after oral administration of glucose in the control NIDDM rats. Increased glucose levels were found to be associated with increased insulin levels. Treatment with amlodipine in the NIDDM rats caused a decrease in insulin release, however, glucose levels were found to be lowered significantly indicating that amlodipine causes an increase in insulin sensitivity. In conclusion, our data indicated that amlodipine increases insulin sensitivity in neonatal-STZ NIDDM rats.

Evidence for alpha 2-adrenoceptor agonist activity of minoxidil.

The present investigation was undertaken to study the mechanism of action of minoxidil using various smooth muscle preparations. Minoxidil (4.7 x 10(-6) M to 4.7 x 10(-4) M) produced a concentration-dependent inhibition of field stimulation-evoked responses in rat anococcygeus muscle and vas deferens. The inhibition produced by minoxidil was antagonized by yohimbine (2.5 x 10(-7) M). Minoxidil (1.4 x 10(-5) M to 4.7 x 10(-4) M) also produced a concentration-dependent relaxation in oestrogen-primed potassium chloride-depolarized rat uterus. These responses were blocked not only by yohimbine but also by glibenclamide (2.02 x 10(-8) M). Our results suggest that minoxidil possesses alpha 2-adrenoceptor agonist activity in addition to potassium-channel-opening activity.

Effects of chronic treatment with amlodipine in streptozotocin-diabetic and spontaneously hypertensive rats.

Calcium antagonists have been reported to alter insulin secretion and insulin sensitivity. However, there still exists a controversy over the benefits of calcium antagonists in the conditions when diabetes mellitus and hypertension coexist. In the present study the effects of six-week chronic amlodipine treatment (5 mg kg-1 p.o.) on insulin sensitivity and serum lipid levels in streptozotocin (STZ)-diabetic and spontaneously hypertensive (SH) rats were investigated. Intravenous injection of STZ produced glucosuria (> 2%). hyperglycaemia, hypoinsulinemia, polydipsia, polyphagia, loss of body weight, hypercholesterolemia, hypertriglyceridaemia, hypertension and bradycardia. SH rats were found to have significantly higher insulin levels compared to their Wistar controls. Treatment of rats with amlodipine in diabetic and diabetic-hypertensive animals significantly prevented STZ-induced loss of body weight, hypertension and bradycardia. It also significantly prevented STZ-induced hyperglycaemia in both STZ-diabetic Wistar and SH rats. The insulin levels were decreased in the non-diabetic treated Wistar rats but were unaltered in the non-diabetic SH and the diabetic Wistar and SH rats. There was a significant reduction in cholesterol levels in diabetic Wistar and SH rats. In conclusion the present study revealed beneficial effects of amlodipine treatment in hyperinsulinemic, diabetic and/or hypertensive rats.

Effect of chronic treatment with spirapril on biochemical parameters in streptozotocin-diabetic and spontaneously hypertensive rats.

Present investigation was undertaken to study the effects of 6 week treatment with spirapril (2 mg/kg po) on insulin sensitivity, and serum lipid levels in streptozotocin (STZ)-diabetic and spontaneously hypertensive (SH) rats. Treatment of rats with spirapril in diabetic and diabetic with hypertensive animals significantly prevented STZ-induced loss of body weight, hypertension, and bradycardia. It also partially but significantly prevented STZ-induced hyperglycaemia in both diabetic Wistar and SH animals. Insulin level was not altered by spirapril treatment. There was significant reduction in cholesterol levels in the diabetic rats. In conclusion, the present investigation presents a number of beneficial effects of spirapril treatment in diabetic and/or hypertensive rats. Spirapril may be considered as one of the drugs of choice in treatment of hypertension when associated with diabetes

Investigation into the possible mechanisms involved in altered digoxin levels in diabetic patients.

The present study was undertaken to investigate the possible factors which may contribute to the altered digoxin levels in diabetic patients. The digoxin levels were found to be significantly higher in diabetics (1.74 +/- 0.09 ng/ml) as compared to non-diabetics (0.76 +/- 0.07 ng /ml). There was a positive correlation between digoxin levels and glycosylated haemoglobin levels. All diabetic patients had serum creatinine, urea and potassium levels within normal limits. However, serum TSH levels were found to be significantly higher in diabetics as compared to controls. Serum tri-iodo-1-thyronine (T3) levels were found to be lower in diabetics as compared to non-diabetics. Our data suggests that diabetes-mellitus causes alteration of digoxin levels. One of the causes of this increase in digoxin levels may be a tendency towards mild hypothyroidism associated with diabetes mellitus.

Pharmacokinetics of gentamicin in rabbits pretreated with nonsteroidal anti-inflammatory drugs: an interaction study.

Interaction between nonsteroidal anti-inflammatory drugs (NSAIDs) and other drugs occurs relatively frequently because of the wide use of NSAIDs. Such interactions with drugs of narrow therapeutic index used in serious disease states may lead to toxicity. Gentamicin toxicity is based on its concentration in serum, and any alteration in pharmacokinetic parameters may lead to gentamicin accumulation in the body and subsequently to severe nephrotoxicity and ototoxicity. To test this hypothesis, the effect of pretreatment with NSAIDs on gentamicin pharmacokinetics was examined in rabbit. Gentamicin sulfate (5 mg/kg) was administered to rabbits pretreated with aspirin (300 mg/kg), ketorolac tromethamine (3 mg/kg), ibuprofen (20 mg/kg), and piroxicam (2 mg/kg) twice a day for 1 week. The pretreatment with NSAIDs had significant effects on the body clearance and maximum concentration. Aspirin, piroxicam and ketorolac tromethamine pretreatment had significant effects on the area under the curve of gentamicin versus time. Aspirin and ketorolac tromethamine pretreatment had significant effects on the half-life of gentamicin. Aspirin had a significant effect on the volume of distribution of gentamicin. These results suggest that pretreatment with NSAIDs alters the pharmacokinetics of gentamicin and leads to accumulation inside the body, which could result in toxicity.