Bioaccumulation of Polychlorinated Biphenyls (PCBs) in Atlantic Sea Bream (Archosargus rhomboidalis) from Kingston Harbour, Jamaica.

Multiple sizes of Sea bream were collected from Kingston Harbour, Jamaica, to assess steady state bioaccumulation of polychlorinated biphenyls (PCBs) in a tropical fish. Sea beam fork lengths ranged from 7.3 to 21.5 cm (n = 36 fish) and tissue lipids decreased with body length. Larger fish had lower δ13C isotopes compared to smaller fish, suggesting a change in diet. Linear regressions showed no differences in lipid equivalent sum PCB concentrations with size. However, differences in individual congener bioaccumulation trajectories occurred. Less hydrophobic PCBs decreased with increasing body length, intermediate PCBs showed no trend, whereas highly hydrophobic (above log KOW of 6.5) PCBs increased. The different congener patterns were interpreted to be a result of decreases in overall diet PCB concentrations with increased fish length coupled with differences in PCB toxicokinetics as a function of hydrophobicity yielding dilution, pseudo-steady state and non-steady state bioaccumulation patterns.

The effects of S-nitrosoglutathione and S-nitroso-N-acetyl-D, L-penicillamine in a rat model of pre-eclampsia.

BACKGROUND: Pre-eclampsia (PE) complicates approximately 5-7% of all pregnancies. This study investigates the effects of S-nitroso-N-acetylpenicillamine (SNAP) and S-nitrosoglutathione (GSNO) on the classical features of PE. MATERIALS AND METHODS: On day 14 of gestation, female Sprague-Dawley rats were separated into five groups and treated intravenously for 7 days as follows: (i) 0.3 mL 0.9% saline (control, n = 11); (ii) 50 mg/kg Body Weight (BW) N-nitro-L-arginine methyl ester (L-NAME) in 0.3 mL saline (n = 10); (iii) 50 mg/kg BW L-NAME and 8 mg/kg BW GSNO in 0.15 mL saline (n = 6); (iv) 50 mg/kg BW L-NAME in 0.15 mL saline and 8 mg/kg BW SNAP in 0.15 mL DMSO (n = 9); and (v) 0.15 mL DMSO and 0.15 mL saline (SNAP control, n = 7). Blood pressures were measured on day 14 through day 20, a 4-h urine sample was taken on day 20, and animals were sacrificed on day 21. Pups were counted and weighed individually. RESULTS: SNAP and GSNO significantly decreased systolic, diastolic, and mean arterial pressures in PE-induced rats from day 14 through day 20 (P < 0.05). Pup weights in SNAP and GSNO groups were higher than in L-NAME group but lower than in controls (P ≤ 0.001). SNAP and GSNO partially reversed growth retardation. CONCLUSION: Elevated blood pressure, proteinuria, and intrauterine growth restriction associated with PE were induced in Sprague-Dawley rats using L-NAME. These were partially reversed with the use of GSNO and SNAP. The mechanism of action of these S-nitrosothiols (RSNOs) should be further explored.

Acrylamide in Caribbean foods - residual levels and their relation to reducing sugar and asparagine content.

The acrylamide levels in commercial and homemade Caribbean foods were determined by pre-derivatisation of acrylamide to 2-bromopropenamide and analysed by gas chromatography with mass spectrometric (GC/MS) detection. Over 100 Caribbean food samples were analysed for the presence of acrylamide. These samples include: biscuits, breakfast cereals, banana chips and home-prepared foods: breadfruit; Artocarpus altilis, banana fritters, and dumplings. The limit of detection (LOD) for the GC/MS method was found to be dependent on the type of column used for the GC/MS analysis. The DB-1701 and the DB-VRX columns gave LODs of 20 and 4 µg/kg, respectively. Acrylamide has not been found in raw foods or foods which have been cooked by boiling. Its content in all other foods had concentrations in the range, 65-3,640 µg/kg. The relationship between acrylamide levels and precursor concentration as well as the health implications of our findings are discussed.

The effect of nitric oxide inhibitors and Snitroso-Nacetylpenicillamine on glucose concentration in an animal model.

BACKGROUND: Nitric oxide (NO) is becoming an increasingly important signaling molecule implicated in a growing number of physiological and pathophysiological processes. Research on the effect of NO donors on glucose metabolism in peripheral tissues have grown rapidly in the last decade. This study examined the effects of N(G)methyl-L-arginine acetate (L-NMMA) and N(G)methyl-L-arginine ester (L-NAME) on fasting and postprandial blood glucose concentrations. The study also investigated if L-NMMA and L-NAME decrease the hyperglycemic effect caused by the NO donor S-nitrosoN-acetylpenicillamine (SNAP) in normoglycemic rats. RESULTS: L-NAME and L-NMMA significantly lowered the postprandial blood glucose concentrations. Mean postprandial blood glucose concentrations in rats treated with L-NAME were 5.04 ± 0.07 mmol/L at 120 min, 4.62 ± 0.19 mmol/L at 150 min and 4.36 ± 0.17 mmol/L at 180 min time points compared with 5.46 ± 0.14 (P = 0.029), 5.20 ± 0.17 mmol/L (P = 0.036), and 4.89 ± 0.14 mmol/L (P = 0.015) at the same time points respectively for saline control. Mean blood glucose concentrations in rats treated with L-NMMA were 4.35 ± 0.23 mmol/L (P = 0.0018) at 120 min, 4.60 ± 0.14 mmol/L (P = 0.090) at 150 min and 3.88 ± 0.16 mmol/L (P 0.001) at 180 min. There were significant differences in mean postprandial blood glucose concentrations in rats treated with SNAP, compared with those treated with L-NAME and SNAP at 90 min (P = 0.012), 180 min (P = 0.013) and 210 min (P < 0.0001). In addition, there were significant differences in mean postprandial blood glucose concentrations in rats treated with SNAP compared with those treated with L-NMMA and SNAP at 90 min (P = 0.0011), 180 min (P = 0.015) and 210 min (P = 0.0077). CONCLUSION: The nitric oxide synthase [NOS] inhibitors were effective in reducing postprandial blood glucose concentration in rats treated with SNAP. This suggests that although SNAP is an effective antihypertensive agent it decreases glucose tolerance which can be improved by the use of NOS inhibitors such as L-NMMA or L-NAME. These drugs could be beneficial in controlling blood glucose tolerance in rats administered with SNAP, and possibly in humans.

Dynamic studies of transnitrosation of thiols of biological importance by the nitrosated 4,4',4'',4'''-tetrasulfophthalocyaninecobaltate(III) anion in aqueous solution.

The kinetics of interaction of Co(III)TSPcNO (TSPc = 4,4',4'',4'''-tetrasulfophthalocyanine) with various thiols of biological relevance, e.g., reduced glutathione (GSH), captopril (CapSH), N-acetyl-L-cysteine (NALC), and L-cysteine ethyl ester (LCEE) have been investigated spectrophotometrically. The observed rate constants for transnitrosation are all first-order with respect to the respective thiols. The second-order rate constants which were determined at physiological temperature, 37 degrees C are 258+/-8, 159+/-3, 66.7+/-1.3 and 37.4+/-0.6 M(-1) s(-1), respectively. The second-order rate constants decreased according to the sequence LCEE > CapSH > GSH > NALC. The activation parameters (DeltaH(not equal) and DeltaS(not equal)) were derived from the Eyring's equation. The experimental activation parameters were then correlated by an isokinetic plot, for the reduction of [Co(III)TSPc(NO(-))](4-) by the thiols, making use of the expression: DeltaH(double dagger) = DeltaG(0)(double dagger) + beta(0)DeltaS(double dagger) where DeltaG(o)(double dagger) is the intrinsic free energy of activation, and beta(o) the isokinetic temperature. The plot which showed very good linearity (R(2) = 0.997), gave values of DeltaG(o)(double dagger) (61+/-1 J K(-1) mol(-1)) from the intercept, and beta(o) (260+/-11 K) from the slope. It is concluded that a common mechanism is adhered to in the reduction of Co(III)TSPcNO, irrespective of the type of thiol being used, to give the corresponding S-nitrosothiol, which is further confirmed by high performance liquid chromatography with mass spectrometric detector.

Transfer of nitric oxide from nitrovasodilators to free thiols--evidence of two distinct stages.

Two distinct stages, which can be monitored spectrophotometrically, have been observed for the first time in multiple reactions between thiol, such as l-cysteine and some well-known nitrovasodilators, namely S-nitroso-N-acetyl-d,l-penicillamine (SNAP), S-nitrosoglutathione (GSNO), and S-nitrosocaptopril (SNOCap) in aqueous solution (in the presence of EDTA). The first part of the reaction occurs at stopped-flow time scale ( approximately 10(-2)s(-1)) in one single step and has been found to be transnitrosation; followed by a slow decomposition of the products of the transnitrosation reaction with the formation of a variety of nitrogen products. Reactivity with regard to the first stage occurs in the order GSNO>SNAP>SNOCap. The second stage shows first-order rate constants of the order 10(-4)s(-1), although some degree of complexity exists in elucidating an accurate rate equation with which a comparative study could be done.

The reaction of S-nitroso-N-acetyl-D,L-penicillamine (SNAP) with the angiotensin converting enzyme inhibitor, captopril--mechanism of transnitrosation.

Kinetic studies involving the use of both stopped-flow and diode array spectrophotometers, show that the reaction between SNAP and captopril in the presence of the metal ion sequestering agent, EDTA, occurs in two well-defined stages. The first stage is a fast reaction while the second stage is slow. The first stage has been postulated to be transnitrosation, and the second stage involves the decay of the newly formed RSNO to effect nitric oxide (NO) release. Both stages are found to be dependent on captopril and H+ concentration. The rates of the transnitrosation increased drastically with increasing pH in the first stage, signifying that the deprotonated form of captopril is the more reactive species. In the case of the second stage the variation in pH showed an increase in rate up to pH 8 after which the rate remained unchanged. Both stages were clearly distinguishable and easily monitored separately. Transnitrosation is a reversible reaction with the tendency for the equilibrium to break down at high thiol concentration. Second-order rate constants were calculated based on the following derived expressions: -d[SNAP]/dt=k(f)((K(SHCapSH)[CapSH](t))/(K(SHCapSH)+[H+]))[SNAP]. k(f) is the second-order rate constant for the forward reaction of the reversible transnitrosation process. At 37 degrees C, k(f)= 785 +/- 14 M(-1) s(-1), activation parameters [Delta]H(f)++= 49 +/- 2 kJ mol(-1), (Delta)S(f)++=-32 +/- 2 J K(-1) mol(-1). The activation parameters demonstrate the associative nature of the transnitrosation mechanism. The second stage has been found to be very complex, as a variety of nitrogen products form as predicted before. However, the following expression was derived from the initial kinetic data: rate =k1K[SNOCap][CapS-]/(K[CapS-]+ 1) to give k1= 13.3 +/- 0.4 x 10(-4) s(-1) and K= 5.59 +/- 0.53 x 10(4) M(-1), at 37 degrees C, where k1 is the first-order rate constant for the decay of the intermediate formed during the reaction between SNOCap and the remaining excess CapSH present at the end of the first stage reaction. Activation parameters are (Delta)H1++= 37 +/- 1 kJ mol(-1), (Delta)S1++=-181 +/- 44 J K(-1) mol(-1).

The effect of nitric oxide on glucose metabolism.

Nitric oxide (NO) is an important bioactive signaling molecule that mediates a variety of normal physiological functions, which, if altered, could contribute to the genesis of many pathological conditions, including diabetes. In this study, we examined the possible diabetogenicity of NO by noting differences in the cellular binding of insulin in dogs treated with the NO donor, S-nitrosoglutathione (GSNO) compared to captopril-treated controls. GSNO administration resulted in an abnormality in glucose metabolism which was attributed to decreased binding of insulin to its receptor on the cell membrane of mononuclear leucocytes, 11.60 +/- 0.60% in GSNO-treated dogs compared with 18.10 +/- 1.90% in captopril-treated control (p < 0.05). The decreased insulin binding was attributed to decreased insulin receptor sites per cell, 21.43 +/- 2.51 x 10(4) in GSNO-treated dogs compared with 26.60 +/- 1.57 x 10(4) in captopril-treated controls (p < 0.05). Average affinity analysis of the binding data demonstrated that this decrease in insulin binding was also due to a decrease in average affinity of the receptor on mononuclear leucocytes for insulin. This was evident by a decrease in empty and filled site affinities in GSNO-treated dogs compared with that of captopril-treated dogs (p < 0.05). It appears that GSNO is exerting its effect by decreasing the number of insulin receptor sites and/or decreasing the average receptor affinity. These results provide evidence for a novel role of NO as a modulator of insulin binding and the involvement of NO in the aetiology of diabetes mellitus.

Dynamics of interaction of vitamin C with some potent nitrovasodilators, S-nitroso-N-acetyl-d,l-penicillamine (SNAP) and S-nitrosocaptopril (SNOCap), in aqueous solution.

The reductive decomposition of both SNAP and SNOCap by ascorbate in aqueous solution (in the presence of EDTA) was thoroughly investigated. Nitric oxide (NO) release from the reaction occurs in an ascorbate concentration and pH dependent manner. Rates and hence NO release increased drastically with increasing pH, signifying that the most highly ionized form of ascorbate is the more reactive species. The experiments were monitored spectrophotometrically, and second-order rate constants calculated at 37 degrees C for the reduction of SNAP are k(b)=9.81+/-1.39 x 10(-3) M(-1) s(-1) and k(c)=662+/-38 M(-1) s(-1) and for SNOCap are k(b)=2.57+/-1.29 x 10(-2) M(-1) s(-1) and k(c)=49.7+/-1.3 M(-1) s(-1). k(b) and k(c) are the second-order rate constants via the ascorbate monoanion (HA-) and dianion (A2-) pathways, respectively. Activation parameters were also calculated and are DeltaHb++ =93+/-7 kJ mol(-1), DeltaSb++ =15+/-2 J K(-1) mol(-1) and DeltaHc++ =51+/-5 kJ mol(-1), DeltaSc++ =-28+/-3 J K(-1) mol(-1) with respect to the reactions involving SNAP. Those for the reaction between SNOCap and ascorbate were calculated to be DeltaHb++ =63+/-11 kJ mol(-1), DeltaSb++ =-71+/-20 J K(-1) mol(-1) and DeltaHc++ =103+/-7 kJ mol(-1), DeltaSc++ =118+/-8 J K(-1) mol(-1). The effect of Cu2+/Cu+ ions on the reductive decompositions of these S-nitrosothiols was also investigated in absence of EDTA. SNOCap exhibits relatively high stability at near physiological conditions (37 degrees C and pH 7.55) even in the presence of micromolar concentrations of Cu2+, with decomposition rate constant being 0.011 M(-1) s(-1) in comparison to SNAP which is known to be more susceptible to catalytic decomposition by Cu2+ (second-order rate constant of 20 M(-1) s(-1) at pH 7.4 and 25 degrees C). It was also observed that the reductive decomposition of SNAP is not catalyzed by alkali metal ions, however, there was an increase in rate as the ionic strength increases from 0.2 to 0.5 mol dm(-3) NaCl.

The effect of nitric oxide on glucose metabolism.

Nitric oxide (NO) is an important bioactive signaling molecule that mediates a variety of normal physiological functions, which, if altered, could contribute to the genesis of many pathological conditions, including diabetes. In this study, we examined the possible diabetogenicity of NO by noting differences in the cellular binding of insulin in dogs treated with the NO donor, S-nitrosoglutathione (GSNO) compared to captopril-treated controls. GSNO administration resulted in an abnormality in glucose metabolism which was attributed to decreased binding of insulin to its receptor on the cell membrane of mononuclear leucocytes, 11.60 ± 0.60% in GSNO-treated dogs compared with 18.10 ± 1.90% in captopril-treated control (p < 0.05). The decreased insulin binding was attributed to decreased insulin receptor sites per cell, 21.43 ± 2.51 × 10(4) in GSNO-treated dogs compared with 26.60 ± 1.57 × 10(4) in captopril-treated controls (p < 0.05). Average affinity analysis of the binding data demonstrated that this decrease in insulin binding was also due to a decrease in average affinity of the receptor on mononuclear leucocytes for insulin. This was evident by a decrease in empty and filled site affinities in GSNO-treated dogs compared with that of captopril-treated dogs (p < 0.05). It appears that GSNO is exerting its effect by decreasing the number of insulin receptor sites and/or decreasing the average receptor affinity. These results provide evidence for a novel role of NO as a modulator of insulin binding and the involvement of NO in the aetiology of diabetes mellitus. (Mol Cell Biochem 263: 29-34, 2004).

The enhancement of the hyperglycemic effect of S-nitrosoglutathione and S-nitroso-N-acetylpenicillamine by vitamin C in an animal model.

BACKGROUND: S-nitrosoglutathione (GSNO) and S-nitroso-N-acetlypenicillamine (SNAP) are two of the most common sources of nitric oxide (NO) in the biomedical field. Vitamin C has been known to accelerate the decomposition of GSNO and SNAP increasing the release and availability of NO which is cytotoxic at non-physiological concentrations. The study investigates any potential detrimental effect of vitamin C and GSNO, vitamin C and SNAP on glucose metabolism in normotensive and normoglycemic dogs. RESULTS: The results showed that administration of vitamin C (50 mg/kg) and GSNO (35 mg/kg & 50 mg/kg), or vitamin C (50 mg/kg) and SNAP (10 mg/kg) to overnight fasted dogs resulted in significant elevation of the blood glucose levels, attaining maximum level at the 2.0 or 2.5 h time point postprandially. The elevated blood glucose levels were due to significant reduction in plasma insulin levels in the dogs treated with vitamin C and GSNO, or vitamin C and SNAP (P < 0.05). The decreased insulin response was associated with significant elevation of nitric oxide produced from GSNO and SNAP co-administered with vitamin C, as assessed by plasma nitrate/nitrite levels. CONCLUSIONS: The results indicate that enhanced NO release by vitamin C affects postprandial blood glucose and plasma insulin levels and the reduced glucose tolerance is mainly due to impaired insulin release. The clinical relevance of the findings of this study suggest that hypertensive diabetic patients treated with GSNO or SNAP, who are on vitamin C supplements may be more predisposed to further decrease in their glycemic control.

Decreased insulin binding to mononuclear leucocytes and erythrocytes from dogs after S-nitroso-N-acetypenicillamine administration.

BACKGROUND: Nitric oxide (NO) and oxygen free-radicals play an important part in the destruction of beta-cells in auto- immune diabetes although the precise mechanism of interaction is still not known. This study was designed to examine any possible diabetogenic effect of NO by investigating any differences in cellular binding of insulin to its receptor on the cell membranes of erythrocytes and mononuclear leucocytes of dogs treated with the NO donor, S-nitroso-N-acetylpenicillamine (SNAP) and controls treated with captopril. RESULTS: The result obtained showed decreased binding of insulin to its receptor on the cell membranes of erythrocytes and mononuclear leucocytes. Mononuclear leucocytes from SNAP-treated dogs had decreased ability to bind insulin (16.30 +/- 1.24 %) when compared to mononuclear leucocytes from captopril-treated controls (20.30 +/- 1.93 %). Similar results were obtained for erythrocytes from dogs treated with SNAP (27.20 +/- 1.33 %) compared with dogs treated with captopril (34.70 +/- 3.58 %). Scatchard analysis demonstrated that this decrease in insulin binding was accounted for by a decrease in insulin receptor sites per cell, with mononuclear leucocytes of SNAP-treated dogs having 55 % less insulin receptor sites per cell compared with those of captopril-treated controls (P < 0.05). Average affinity and kinetic analysis revealed a 35 % decrease in the average receptor affinity, with mononuclear leucocytes from captopril-treated controls having an empty site affinity of 12.36 +/- 1.12 x 10(-8) M(-1) compared with 9.64 +/- 0.11 x 10(-8) M(-1) in SNAP-treated dogs (P < 0.05). CONCLUSION: These results suggest that acute alteration of the insulin receptor on the membranes of mononuclear leucocytes and erythrocytes occurred in dogs treated with S-nitroso-N-acetylpenicillamine. These findings suggest the first evidence of the novel role of NO as a modulator of insulin binding and the involvement of NO in the aetiology of diabetes mellitus.

The effects of chronic S-nitrosoglutathoine adminstration on glucose tolerance in dog animal model

The nitric oxide donor S-nitrosoglutathione (GSNO) has been used to prevent platelet activation in patients with severe pre-eclampsia. The study assesses the chronic administration of GSNO on glucose metabolism in the dog animal model. GSNO (10 mg/kg) was administered intravenously for 14 days and the blood glucose concentration was determined by the glucose oxidase method. Oral glucose tolerance tests revealed an impaired glucose tolerance in the GSNO-treated dogs as reflected by elevated postprandial blood glucose concentrations at the 1.0 hour to 2.5 hour time interval (p < 0.05). The elevated blood glucose concentration was associated with a statistically significant decrease in plasma insulin concentration. The plasma insulin concentration at 1.0 hour in captopril-treated controls was 41.00 uIU/ml compared with 27.33 uIU/ml in GSNO-treated dogs (p < 0.05). In contrast, the plasma glucagon concentration was enhanced by the chronic adminstration of GSNO, as confirmed by a concentration of 75.00 ñ 6.06 pg/ml in GSNO-treated dogs compared with 49.50 ñ 4.64 pg/ml in captopril-treated controls at the 1.0 hour time interval. Linear regression analysis of the data revealed a highly significant and positive correlation between the blood glucose concentration and the plasma glucagon concentration (r = 0.739, p < 0.01). Similarly, a positive correlation existed between the blood glucose concentration and the plasma insulin concentration (r = 0.513, p = 0.307). We conclude that chronic in vivo adminstration of GSNO impairs the parameters of carbohydrate metabolism. Patients who are on protracted treatment with GSNO could be risk for the development of diabetes mellitus.(Au)

Fate and transport of ethoprophos in the Jamaican environment

The hydrolytic half lives of ethoprophos in distilled, river, brackish and open sea water were 25, 133, 65 and 81 days, respectively. Under laboratory conditions, volatilisation of the residues after 12 h was 1.4 - 3.6, 2.3 - 4.5 and 6.5 - 20.2 percent from a sandy loam soil with 1, 10 and 20 percent moisture levels, respectively. Photolysis in soil was significantly faster (P< 0.05) in direct sunlight (T 1/2 of 12.3 days). The microbial degradation of ethoprophos from unweeded plantation soil at 23 degrees slope was significantly (P=0.015) less than at 38 degrees slope; the amounts lost after 9 weeks and 27.5 mm of rainfall were 89.4 and 91.2 percent respectively, of the applied amount from the two respective slopes. In the weeded plots, 93.6 and 92.4 percent of the applied insecticide were lost from 23 degrees and 38 degrees slopes, respectively. Under laboratory conditions, between 67.0 and 85.1 percent of ethoprophos leached through the soil columns. Under field conditions, after 9 weeks and 25 mm of rainfall, only 2.8 and 2.0 percent residues were recovered at a depth of 10-15 cm from unweeded and weeded slopes, respectively at 23 degrees slope, and 2.2 and 1.9 percent from the two respective plots at 38 degrees slope. (AU)

The effect of nitric oxide released from s-nitroso-glutathoine on glucagon and insulin in dogs

Nitric oxide (NO), a potent modulator of cellular function, and NO donors have been useful tools in both experimental and clinical setting. Low molecular weight thiols such as cysteine and glutathoine were proposed to act as NO-carriers. The study was undertaken to investigate the pharmacological activity of the NO donor, S-nitrosoglutathoine (GSNO), on the plasma glucose and on the gluco-regulatory hormones, insulin and glucagon in healthy normoglycaemic dogs. Plasma glucose levels were measured by the glucose oxidase method, while the insulin and glucagon levels were determined by radioimmunoassay. In healthy normoglycaemic dogs, administration of 50 mg/kg GSNO caused an increase in post-prandial plasma glucose levels. The plasma glucose levels were significantly (p<0.05) elevated at 1.5 hr, 2.0 hr and 2.5 hr of the oral glucose tolerance test. These values were significantly higher than those obtained for the controls. The increase in glucose level was associated with a significant decrease in insulin levels and increase in glucagon levels (p<0.05). The fasting insulin level was 8.0 ñ 0.3 IU/ml in the control. The insulin level increased to a maximum of 34.0 ñ 0.3 IU/ml 1.5 hr post-prandial, and then decreased to 12.4 ñ 0.4 IU/ml after 2.5 hr. On administration of 50 mg/kg GSNO, the insulin level increased to a maximum of 23.0 ñ 0.6 IU/,l after 1.5 hr post-prandial and then decreased to 17.0 ñ 0.4 IU/ml after 2.5 hr. The blood glucagon levels increased from 40.0 ñ 0.3 pg/ml to 53.0 ñ 0.3 pg/ml after 1 hr in controls. In dogs administered with GSNO, the blood glucagon level increases to a maximum level of 80.0 ñ 0.5 pg/ml 1.5hr post-prandial. These results suggest that in healthy normoglycaemic dogs, nitric oxide released from GSNO caused a transient increase in post-prandial plasma glucose levels, inhibited glucose stimulated insulin secretion and elevated glucagon levels.(AU)

The effect of S-nitroso-glutathione on insulin receptors on erythrocytes abd mononuclear leucocytes in dogs

This study was designed to investigate differences in cellular binding of insulin in dogs administered with the nitric oxide donor, S-nitroso-glutathione (GSNO). A time course assay of insulin binding to isolated erythrocytes and mononuclear leucocytes from dogs administered with GSNO was done during the oral glucose tolerance test (OGTT). The erythrocyte receptor assay performed was the methodology used by Ghambir et al (1977). A modification was also done for mononuclear leucocyte insulin binding assay. The plasma glucose levels were measured by the glucose oxidase method, while the insulin levels were determined by radioimmunoassay. The results of these studies show the erythrocytes and mononuclear leucocytes from dogs administered with GSNO have lesser ability to bind insulin when compared to erythrocytes and mononuclear leucocytes from the controls. In dogs administered with GSNO, there was less binding of erythrocytes and mononuclear leucocytes, 44 percent and 29 percent, respectively, when compared to the bound free ratio value of the controls.(AU)

Decreased insulin binding to erythrocytes and mononuclear leucocytes in normal dogs administered with S-nitroso- glutathione

Nitric oxide is a pathogenic factor of inflammatory islet cell death in type 1 diabetes. An early event in the pathogenesis of insulin-dependent diabetes mellitus (IDDM) is intraislet accumulation of activated macrophages. Their secretory products such as nitric oxide (NO) are found to play a crucial role in islet destruction. Macrophage activity and progressive islet cell destruction persist during a long period of chronic inflammatory events preceding diabetes, suggesting the presence of nitric oxide contributing to continued immunostimulation. It has been shown previously that the nitric oxide donor, S-nitrosoglutathione (GSNO) caused persistent postprandial hyperglycaemia in normal healthy dogs at 35 and 50mg/kg. parallel with an increase in plasma nitrate concentration and decrease in insulin secretion. This study was designed to investigate differences in cellular binding of insulin in dogs administered with the GSNO. A time course assay of insulin binding, to isolate erythrocytes and mononuclear leucocytes from dog administered with GSNO, was done during the oral glucose tolerance test (OFTT). The erthrocyte receptor assay performed was the methodology used by Ghambir et al (1977). A modification was also done for mononuclear leucocytes insulin binding assay. The plasma glucose levels were measured by the glucose oxidase method, while the insulin levels were determined by radio-immunoassay. The results of these studies show that erythrocytes and mononuclear leucocytes from dogs administered with GSNO have decreased ability to bind insulin when compared to erythrocytes and mononuclear leucocytes from the controls. In dogs administered with GSNO, there was less binding of erythrocytes and mononuclear leucocytes, 44 percent and 29 percent respectively, when compared to the bound free ratio value of the controls. The data also shows that erythrocytes and mononuclear leucocytes from dogs administered with GSNO have 256 and 10.7x10 insulin receptor sites per cell, respectively, compared with 296 and 18.4x10 per cell for the control (P<0.05). Competitive inhibition studies using unlabelled insulin indicate that the affinity of insulin for its receptor on erythrocytes from dogs administered with GSNO was also significantly different from the controls, while that of mononuclear leucocytes from both group was comparable.(AU)

The hyperglycaemic effect of s-nitroso-glutathione via the release of nitric oxide - abstract

Recent evidence suggests that nitric oxide (NO) is an important factor in both inflammatory-induced and streptozotocin-induced diabetes. In this study we investigated the pharmacological activity of S-nitroso-glutathoine (GNSO), a carrier of NO, on blood glucose level in 10 mongrel dogs, and measured their plasma nitrate concentration after the administration of GSNO. S-nitroso-glutathoine elicited a dose-dependent increase in blood glucose level (15 - 102 percent) which was paralled with an increase in nitrate production. The blood glucose levels at 2.0 and 2.5 hrs in an Oral Glucose Tolerance Test were significantly higher in dogs administered with GNSO than those of the controls (p<0.05). There was also a significant increase in plasma nitrate on administration of GSNO (35 - 100 percent). The plasma nitrate concentrations from 0.5hr to 2.5hrs were significantly higher compared to the controls (p<0.05). The hyperglycaemic effect of GSNO was enhanced with the co-adminstration of ascorbic acid. This resulted in 5 - 30 percent increase in blood glucose concentration. The blood glucose levels at 2hrs in dogs after the co-administration of 35mg kg of GSNO (P<0.05). The data from this study showed that persistent hyperglycemia can be an unwanted side effect of GSNO administration and that the glucose concentration should be closely monitored when this drug is used to treat patients(AU)

The hyperglycaemic effect of S-nitroso-glutathione via the release of nitric oxide

Nitric oxide is a pathogenic factor of inflammatoryislet cell death in Type I diabetes. Insulin-Dependent Diabetes Mellitus (IDDM) is mediated by an autoimmune mechanism or inflammatory process that is characterized by destruction of beta cells. Incubation of pancreatic islet cells with activated macrophages, which release large amounts of nitric oxide, causes the death of the islet cells. When the cells are exposed to the nitric oxide donor, sodium nitroprusside, lysis of the cells occur in a concentration and time-dependent manner. In this study we investigated the pharmacological activity of S-nitroso-glutathione (GSNO), a carrier of nitric oxide on blood glucose levels in dogs, and measured the plasma nitrate/nitrite concentration in the dog serum after the administration of GSNO using an automated method. The blood glucose level was measured using the glucose oxidase assay. S-nitroso-glutathione elicited a dose-dependent increase in blood glucose levels which was paralleled with an increase in nitrate/nitrite production. The blood glucose levels at 2.0 hrs and 2.5 hrs of the Oral Glucose Tolerance Test (OGTT) were significantly higher in dogs administered with GSNO than those of the controls (p<0.05). Post-prandial blood glucose levels in dogs administered with 35 mg per kg body weight of GSNO were 7.2 + 0.9mmol/l and 7.1 + 0.7mmol/l, compared with 4.8 + 0.2mmol/l and 4.6 + 0.2mmol/l in controls. The hyperglycaemic effect was more pronounced on adminstration of 35 mg per kg body weight of GSNO and ascorbic acid. Post-prandial blood glucose levels in the dogs after administration of 50 mg per body weight, at 2.0 hrs and 2.5 hrs were 9.2 + 0.7mmol/l and 9.3 + 0.3mmol/l, respectively. The basal nitrate/nitrite concentration was 12.4 + 0.4umol. On administration of 35 mg per kg body weight of GSNO, there was a 35 - 60 percent increase in the plasma nitrate/nitrite concentration. The plasma nitrate/nitrite concentration at 2.0 hrs to 2.5 hrs ranged from 16.8 + 1.0umol. The plasma nitrate/nitrite concentration increase by 100 percent on administration of 50 mg per kg of GSNO. This study confirms that S-nitroso-glutathione is a hyperglycaemic compound which affects the blood glucose levels in dogs. The hyperglycaemic effects can be caused by the nitric oxide action on the pancreatic islet cells (AU).