The plasma protein binding of drugs has been shown to have significant effects on numerous aspects of clinical pharmacokinetics and pharmacodynamics. In many clinical situations, measurement of the total drug concentration does not provide the needed information concerning the unbound fraction of drug in plasma which is available for distribution, elimination, and pharmacodynamic action. Thus, accurate determination of unbound plasma drug concentrations is essential in the therapeutic monitoring of drugs. Many methodologies are available for determining the extent of plasma protein binding of drugs, however, in the clinical evaluation of drug therapy, equilibrium dialysis and ultrafiltration are the most routinely utilised methods. Both of these methods have been proven to be experimentally sound and to yield adequate protein binding data. Furthermore, the characterisation of the interactions between drug and protein molecules is essential for the assessment of the pharmacokinetic implications of drug-protein binding. Protein binding parameters which characterise the affinity of the drug-protein association, the number of classes of binding sites, the number of binding sites per class or protein and the binding capacity are useful for predicting unbound drug concentrations. Simple graphical methods have often been used to obtain protein binding parameters, but these methods have limitations and are not useful for drugs with more than 1 class of binding site. Therefore, the fitting of protein binding models which characterise the drug-protein binding interaction for experimental data is the preferred method of calculating binding parameters. Using the appropriate model, values for binding parameters are typically estimated by using nonlinear least-squares regression analysis.

Background-Spinal cord stimulation (SCS) reduces the incidence of ventricular tachyarrhythmias in experimental models. This study investigated the effects of long-term SCS on ventricular function in a postinfarction canine heart failure model. Methods and Results-In stage 1, dogs underwent implantable cardioverter-defibrillator implantation and embolization of the left anterior descending artery followed by right ventricular pacing (240 ppm) for 3 weeks to produce heart failure. In stage 2, 28 surviving animals were assigned to the SCS (delivered at the T4/T5 spinal region for 2 hours 3 times a day), medicine (MED; carvedilol therapy at 12.5 mg PO BID), or control (CTRL; no therapy) group for the initial phase 1 study. In a subsequent phase 2 study, 32 stage 1 survivors were equally randomized to the SCS, MEDS (carvedilol plus ramipril 2.5 mg PO QD), SCS plus MEDS (concurrent therapy), or CTRL group. Animals were monitored for 5 weeks (phase 1) or 10 weeks (phase 2). In stage 3, all phase 1 animals underwent circumflex artery balloon occlusion for 1 hour. In the SCS group, left ventricular ejection fraction was 65Ϯ5% at baseline, 17Ϯ3% at the end of stage 1, and 47Ϯ7% at the end of stage 2. In the MED group, left ventricular ejection fraction was 61Ϯ4% at baseline, 18Ϯ3% at the end of stage 1, and 34Ϯ4% at the end of stage 2. In the CTRL group, left ventricular ejection fraction was 64Ϯ5% at baseline, 19Ϯ5% at the end of stage 1, and 28Ϯ3% at the end of stage 2. Left ventricular ejection fraction was significantly improved in the SCS compared with the MED and CTRL groups (PϽ0.001 for both). The mean number of spontaneous nonsustained ventricular tachyarrhythmias during stage 2 and the occurrence of ischemic ventricular tachyarrhythmias during stage 3 also were significantly decreased in the SCS (27Ϯ17 and 27%, respectively; PϽ0.03) and MED (58Ϯ42 and 33%; PϽ0.05) versus CTRL (88Ϯ52 and 76%) group. After 10 weeks in the phase 2 studies, the greatest recovery in ejection fraction was noted in the SCS (52Ϯ5%) and SCSϩMEDS (46Ϯ4%) groups compared with the MEDS (38Ϯ2%) and CTRL (31Ϯ4%) groups. Conclusion-SCS

Abstract-This study assessed the effect of metformin treatment on insulin, mean arterial pressure (MAP), and endothelial function in insulin-resistant (IR) rats. In addition, we assessed the direct effect of metformin in vitro. Sprague-Dawley rats were randomized to control (nϭ28) or IR (nϭ28) groups. Rats were further randomized to receive metformin (300 mg/kg) or placebo for 2 weeks. MAP and insulin were measured. Subsequently, a third-order branch of the superior mesenteric artery was isolated, and endothelial function was assessed. Specifically, dose-response experiments of acetylcholine (ACh) with or without N-nitro-L-arginine (LNNA) were performed. For in vitro experiments, mesenteric arteries were removed from untreated control and IR rats and treated with metformin (100 mol/L) before AChϮLNNA. MAP and insulin levels were improved in IR-metformin compared with IR-placebo rats. Maximal relaxation (E max ) to ACh was enhanced in IR-metformin (92Ϯ2%) compared with IR-placebo rats (44Ϯ4%) (PϽ0.05). Relaxation in response to AChϩLNNA was greater in IR-metformin (33Ϯ4%) than in IR-placebo rats (12Ϯ4%) but remained depressed compared with control rats (E max ϭ68Ϯ5%). The control group was not affected by metformin. In vitro treatment of arteries with metformin in response to ACh produced results similar to those in the experiments with metformin-treated rats. Although metformin improves metabolic abnormality in IR rats, this action does not appear to mediate its effect on vascular function. Both in vivo and in vitro metformin improved ACh-induced relaxation in IR rats to control levels, apparently through nitric oxide-dependent relaxation. These data suggest that metformin improves vascular function through a direct mechanism rather than by improving metabolic abnormalities. Key Words: insulin resistance Ⅲ relaxation Ⅲ metformin Ⅲ nitric oxide Ⅲ blood pressure E xcess cardiovascular morbidity and mortality in patients with type 2 diabetes mellitus (non-insulin-dependent diabetes mellitus) is not explained by the presence of traditional cardiovascular risk factors. 1,2 In addition, glucose control with traditional agents, such as sulfonylureas or insulin, does not alter the risk of macrovascular complications. 3 Epidemiological and observational studies suggest that insulin resistance (IR) may play a role in the development of vascular disease in type 2 diabetes mellitus. 4 -6 Moreover, a recent study has shown that treatment of obese type 2 diabetes mellitus patients with metformin, an insulinsensitizing agent, improves cardiovascular sequelae. 7 Taken together, these data suggest that IR is an important risk factor for the development of cardiovascular disease. Unfortunately, the underlying mechanism(s) by which IR promotes vascular disease remains unknown. Previous data from our laboratory and others suggest endothelial dysfunction as a possible mechanism linking IR to vascular disease. 8,9 Specifically, we have shown that endothelium-dependent relaxation is impaired in IR rats because of a defect in nitric o...