In vitro effect of dibenzyl trisulfide on the p50 of the oxygen haemoglobin dissociation curve.

OBJECTIVES: Dibenzyl trisulfide (DTS) has been reported to have cytotoxic and anti-inflammatory effects. It also affects erythrocyte deformability. We investigated the effects of DTS on the p50 of the oxygen haemoglobin dissociation curve. METHODS: Blood samples from 10 healthy male volunteers with normal haemoglobin AA were exposed to 50, 100, 200 and 400 ng/mL, respectively, of DTS. A hemox-analyzer was used to obtain the p50 values. RESULTS: The mean p50 value for the control samples was 25.89 ± 2.18 mm Hg. The values for the samples exposed to 50, 100, 200 and 400 ng/mL were 23.53 ± 1.81 mm Hg, 22.62 ± 1.61 mm Hg, 21.88 ± 1.67 mm Hg and 21.68 ± 1.88 mm Hg, respectively. CONCLUSIONS: DTS caused a significant (p<0.001) reduction in p50 values indicating a shift of the oxygen- haemoglobin dissociation curve to the left in all the samples compared with control, suggesting that the administration of DTS could result in decrease in oxygen supply to tissues.

Serotonin-2B/2C Receptors Mediate Bovine Ciliary Muscle Contraction: Role in Intraocular Pressure Regulation.

PURPOSE: To study the pharmacological profile of the serotonin (5-hydroxytryptamine [5-HT]) receptor subtype mediating contractions in bovine isolated ciliary muscles. METHODS: Ciliary muscle strips were isolated from bovine eyeballs and mounted in organ baths containing aerated (95% O2, 5% CO2) Krebs buffer solution maintained at 37°C. Each muscle strip was attached at 1 end to a Grass Force-displacement Transducer connected to a Polyview Computer System for recording changes in isometric tension. After an equilibration period, ciliary muscle strips were exposed to selective agonists and antagonists of 5-HT receptors. RESULTS: Both selective and nonselective agonists for 5-HT produced concentration-dependent contractions of isolated ciliary muscles with the following rank order of potency: BW723C86>α-methyl-5-HT>MK-212>>8-hydroxy-DPAT>quipazine>R-DOI>>5-HT>>tryptamine. The selective 5-HT2 receptor antagonists, M-100907 (5-HT2A), RS-127445 (5-HT2B), and RS-102221 (5-HT2C), produced noncompetitive inhibition of the contractile effects of selective agonists yielding antagonist potency (pKB) values of 251 ± 27.2 nM (n = 4), 52.5 ± 6.3 nM (n = 4), and 79.4 ± 9.5 nM (n = 4), respectively. CONCLUSION: On the basis of the profile of activity of selective agonists and antagonists, we conclude that the 5-HT2B and 5-HT2C receptor subtypes appear to be the predominant serotonin receptors that mediate the contractile action of this amine in bovine isolated ciliary muscles.

Pharmacology of Serotonin Receptors Causing Contraction of Isolated Bovine Posterior Ciliary Arteries: Role in Ocular Blood Flow.

PURPOSE: To determine the serotonergic (5HT) receptor subtype mediating the contraction of bovine posterior ciliary arteries (BPCAs) in vitro. METHODS: Longitudinal isometric tension was measured in BPCA strips (4-5 mm) mounted in 25 mL organ baths containing oxygenated Krebs solution at 37°C. Cumulative contractile concentration-response (C-R) curves were generated for various 5-HT agonists to assess their potencies and maximal degrees of contraction. Multiple agonist C-R curves were also constructed in the presence and absence of receptor-selective antagonists to determine antagonist potencies using Schild plots. RESULTS: Selective and nonselective agonists for 5-HT receptors elicited concentration-dependent contractile responses in BPCAs with the following rank order of potency: MK-212 > BW723C86 > α-methyl-5-HT >5-methoxy-α-5-methyl-5-HT >> R-DO1 > >5-HT >> cabergoline >> 5-methoxy-dimethyl-tryptamine >> 2-methyl-5-HT >> tryptamine. Interestingly, both 8-OH-DPAT (5HT1A agonist) and quipazine (5HT3 agonist) did not elicit contractions in BPCAs. The contractions produced by BW723C86 (5-HT2B agonist) were antagonized by 5-HT receptor blockers, RS-127445 (5-HT2B antagonist), and M-100907 (5-HT2A antagonist), yielding antagonist pA2 values of 7.5 ± 0.12 (n = 4) and 6.2 ± 0.17 (n = 4), respectively. Furthermore, contractions elicited by MK-212 (5-HT2C agonist) was blocked by RS-102221 (5-HT2C antagonist), although noncompetitively. CONCLUSIONS: On the basis of the pharmacological profile of selective agonists and antagonists, we conclude that serotonin-induced contractions of the BPCA are mediated primarily by a combination of 5HT2C and/or 5HT2B receptors. It appears that 5-HT1A and 5-HT3 receptors are not involved in the contractile action of BPCAs to serotonin.

Effect of cilostazol on the p50 of the oxygen-hemoglobin dissociation curve.

Cilostazol is a drug used for the treatment of intermittent claudication caused by narrowing of the blood vessels and reduced oxygen supply, characterized by intense pain in the leg when walking. This study was designed to investigate the effect of cilostazol on the P50 of the oxygen hemoglobin dissociation curve. A total of eight healthy adult subjects were studied. Blood samples (0.5 mL) from each subject were mixed with 5, 10, and 20 µL of the 0.5 mg/mL stock solution of cilostazol to give concentrations of 10, 20, and 40 µg/mL equivalent to adult doses of 50, 100, and 200 mg, respectively. The control sample had no drug added. The oxygen hemoglobin dissociation curve of each sample was plotted and the P50 determined with a Hemox-Analyzer (TCS, Medical Products Division, Southampton, PA). The mean P50 for the control samples was 28.27 ± 0.43 mm Hg. The values of the samples exposed to 10, 20, and 40 µg/mL cilostozol were 29.63 ± 0.66, 30.15 ± 0.77, and 31.66 ± 0.62 mm Hg, respectively. There was a statistically significant difference (p < 0.01) between the control and samples exposed to 40 µg/mL cilostazol. This study suggests that cilostazol caused an increase in the release of oxygen from hemoglobin as shown in the P50 values. This effect was significant at the highest concentration of 40 µg/mL.

Renal and Hepatic Function in Hypercholesterolemic Rats Fed Jamaican Bitter Yam (Dioscorea polygonoides).

BACKGROUND: We reported that Jamaican bitter yam (Dioscorea polygonoides) has antilipemic potential in rats; however there is limited data on the toxicological profile of the yam. We therefore investigated the effects of bitter yam consumption for 6 or 12 weeks on renal and hepatic function in rats fed a high (4%) cholesterol diet. METHODS: Twenty four rats were divided into six groups (n = 4); three of which were used for each investigation (6 or 12 weeks). One group was administered 4% cholesterol diet, while the yam group had the cholesterol diet supplemented with 5% bitter yam. The control group was fed standard rat chow. Liver and kidney function tests were performed on serum, liver and kidney. Histological studies were conducted on liver samples. Acute toxicity tests were performed in rats and mice administered a single high dose of bitter yam (10 g/kg). RESULTS: Activities of liver and kidney AST and ALT differed (p ≤ .02) between control rats and those fed cholesterol with bitter yam for 12 weeks. Albumin to globulin ratio was reduced (p = .03) in rats fed cholesterol with bitter yam for 6 weeks as compared to the control group. Serum urea concentration was higher (p < .05) in rats fed bitter yam as compared to normal chow for 6 weeks. The cholesterol diet caused extensive fat deposition in liver cells; however this was inhibited by co-administration of bitter yam. CONCLUSION: Long-term administration of Jamaican bitter yam may induce slight changes in renal and hepatic functions.

Effects of Jamaican bitter yam (Dioscorea polygonoides) and diosgenin on blood and fecal cholesterol in rats.

A sapogenin-rich preparation from Jamaican bitter yam (Dioscorea polygonoides) has been shown to reduce blood cholesterol concentrations in hypercholesterolemic rats and mice. Also, diosgenin supplementation has been reported to have antilipemic effects in several animal species. We investigated potential mechanisms of the lipid-lowering actions of bitter yam and also whether the actions were mediated by diosgenin. Sprague-Dawley rats were fed a hypercholesterolemic diet (4% cholesterol) alone or with 5% bitter yam or 1% diosgenin supplementation for 6 weeks. The control group was fed normal rat chow. The serum lipid profile, fecal cholesterol concentration, and serum lipase activity were assessed at the end of the period. The induction of hypercholesterolemia was inhibited by coadministration of 5% bitter yam or 1% diosgenin in the diet. Serum lipid profiles were similar in rats fed bitter yam or diosgenin. The fecal cholesterol concentration was significantly (P < .01) higher in rats fed diosgenin compared to the cholesterol group. However, there was no corresponding elevation in the group fed bitter yam. Administration of bitter yam or diosgenin supplement significantly increased (P < .01) the serum lipase activity compared to the normal control and cholesterol groups. The cholesterol-supplemented diet inhibited normal gain in body weight over the period. This action was potentiated by diosgenin. The effects of the respective supplements on body weight were not completely explained by food consumption. Supplementation of the diet with Jamaican bitter yam may be therapeutically beneficial in the management of hypercholesterolemia.

Inhibitory action of hydrogen sulfide on muscarinic receptor-induced contraction of isolated porcine irides.

We investigated the pharmacological actions of hydrogen sulfide (H(2)S) using sodium hydrosulfide (NaHS) and sodium sulfide (Na(2)S) as donors on isolated porcine irides in the presence of tone induced by muscarinic receptor stimulation. Furthermore, we also investigated the mechanism of action of H(2)S in this smooth muscle. Isolated porcine iris muscle strips were set up in organ baths and prepared for measurement of longitudinal isometric tension. The relaxant action of NaHS or Na(2)S on carbachol-induced tone was studied in the absence and presence of a K(+)-channel inhibitor and inhibitors/activators of enzymes of the biosynthetic pathways for H(2)S, prostanoid and nitric oxide production. In the concentration range, 10 nM to 100 microM, NaHS produced a concentration-dependent relaxation of carbachol-induced tone reaching a maximum of inhibition of 28% at 30 microM. The cyclooxygenase inhibitor, flurbiprofen (1 microM), enhanced relaxations induced by both NaHS and Na(2)S yielding IC(50) values of 7 microM and 70 microM, respectively. With exception of l-NAME (300 muM) inhibitors of cystathionine gamma-lyase, propargylglycine, (PAG) (1 mM) and beta-cyanoalanine, (BCA) (1 mM) and inhibitors of cystathionine beta-synthase, aminooxyacetic acid (AOA) (30 microM) and hydroxylamine (HOA) (30 microM) caused significant (P < 0.001) rightward shifts in the concentration-response curves to NaHS. An activator of cystathionine beta-synthase, SAM (100 microM), enhanced relaxations elicited by low concentrations of NaHS but attenuated responses caused by the higher concentrations of this H(2)S donor. The inhibitor of K(ATP) channel, glibenclamide (100 and 300 microM), blocked relaxations induced by NaHS. We conclude that the observed inhibitory action of NaHS and Na(2)S in isolated porcine irides is dependent on endogenous production of prostanoids and the biosynthesis of H(2)S by cystathionine gamma-lyase and cystathionine beta-synthase. Furthermore, relaxation induced by H(2)S is mediated, at least in part, by K(ATP) channels. Nitric oxide is not involved in the relaxation induced by this gas in the isolated porcine irides.