Brain ischemia was induced for 10 or 30 min by clamping the common carotid arteries in rabbits whose vertebral arteries had previously been electrocauterized. EEG and tissue content of high energy phosphates were used to verify the ischemic state and to evaluate the degree of postischemic recovery. Extracellular levels and total contents of amino acids were followed in the hippocampus during ischemia and 4 h of recirculation. At the end of a 30-min ischemic period, GABA had increased 250 times, glutamate 160 times, and aspartate and taurine 30 times in the extracellular phase. The levels returned to normal within 30 min of reflow. A delayed increase of extracellular phosphoethanolamine and ethanolamine peaked after 1–2 h of reflow. Ten minutes of ischemia elicited considerably smaller but similar effects. With respect to total amino acids in the hippocampus, glutamate and aspartate decreased to 30–50% of control while GABA appeared unaffected after 4 h of reflow. Alanine, valine, phenylalanine, leucine, and isoleucine increased severalfold. The importance of toxic extracellular levels of excitatory amino acids, as well as of high extracellular levels of inhibitory amino acids, are considered in relation to the pathophysiology of neuronal cell loss during cerebral ischemia.

Fulminant hepatic failure was induced in rabbits by intravenous administration of galactosamine hydrochloride. The animals were sacrificed after 45 h and the hippocampus analyzed for free amino acids. In addition, free amino acids were measured in plasma and in the extracellular fluid of the hippocampus 20, 30 and 45 h after galactosamine injection. The extracellular fluid compartment was analyzed by slow perfusion of a thin dialysis tube which was implanted in the hippocampus one day prior to galactosamine administration. The amino acid concentration in the extracellular fluid agreed fairly well with that of the cerebrospinal fluid in the control situation. During development of hepatic failure, the plasma concentration of all amino acids increased. The changes in extracellular amino acids were smaller, except for phosphoethanolamine and glutamate. The concentration ratio intra/extracellular amino acids decreased in the hippocampus for amino acids with a normally high concentration gradient.

Aims/hypothesisRecent evidence suggests that reduced synthesis of nitric oxide in endothelial cells, i.e. endothelial dysfunction, contributes to the impaired action of insulin in the vasculature of patients with type 2 diabetes. We investigated whether selective inhibition of phosphodiesterase-5 by tadalafil has beneficial effects on peripheral microcirculation and glucose uptake in these patients.MethodsWe enrolled seven postmenopausal women with type 2 diabetes and ten age-matched healthy women as controls in a placebo-controlled study to evaluate the acute metabolic effects of tadalafil. We performed microdialysis and blood flow measurements in muscle, and sampled arterial and deep venous blood before and after a single dose of tadalafil 20 mg or placebo. Circulating glucose and insulin levels, muscle capillary recruitment as reflected by permeability surface area for glucose (PSglu) and forearm glucose uptake were measured.ResultsIn women with type 2 diabetes, but not in the control group, tadalafil induced increases in the incremental AUC for PSglu (tadalafil vs placebo 41 ± 11 vs 4 ± 2 ml [100 g]−1 min−1, p < 0.05) and forearm glucose uptake (46 ± 9 vs 8 ± 4 µmol [100 g]−1 min−1, p < 0.05). The variable that best predicted forearm glucose uptake was PSglu, which explained 70% of its variance. However, fasting glucose and insulin concentrations were similar following treatment with placebo or tadalafil in the two groups.Conclusions/interpretationThis study suggests that tadalafil evokes positive metabolic effects in insulin-resistant women with type 2 diabetes.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-010-1819-4) contains supplementary material, which is available to authorised users.

Abstract— The uptake of the neurotransmitter candidates glutamate and aspartate into synaptosomes and bulk‐isolated glia was considerably more rapid than the uptake of the suspected transmitter‐precursor glutamine at low concentrations (10 μM). Glial uptake in all cases was one‐fifth to one‐third of synaptosomal, whereas isolated neurons attained very low tissue: medium ratios, probably reflecting damage to the neurons sustained during isolation. The glial and synaptosomal uptakes of glutamate both obeyed dual high‐ and low‐affinity kinetics and were negligible in the absence of external sodium, whereas glutamine was taken up in either case by an exclusively low‐affinity transport system exhibiting no sodium‐dependence. Glutamine was considerably metabolized to glutamate following transport by both glia and synaptosomes whereas glutamate remained unmetabolized

The aim of the study was to evaluate how implantation of a dialysis probe influences the blood-brain barrier. Leakage of endogenous serum albumin was evaluated by Evans blue/albumin staining and by immunohistochemistry . The passage from blood to dialysate of two substances that normally do not pass into the brain, [3H]inulin and glutamate, was studied 3 and 24 h after insertion of a dialysis probe. Evans blue, given 20 min before rats were killed, was observed around the probe and surrounding brain tissue . Albumin immunoreactivity was seen at considerable distance from the probe with larger spread at 24 h than at 3 h after probe insertion . Glutamate and [3H]inulin were detected in the dialysate with no significant further increase of radioactivity after intracarotid infusion of protamine sulfate that enhances the permeability over the blood-brain barrier. When protamine was followed by infusion of glutamate, the concentrations of taurine increased in the dialysate in four of eight rats . That plasma constituents have access to the brain around the dialysis probe is essential to consider, particularly in studies using substances and drugs that do not pass an intact blood-brain barrier. Key Words: Microdialysis-Blood-brain barrier-Amino acids-Protamine sulfate-Glutamate-Inulin.Abbreviations used : ßBß, blood-brain barrier ; MAP, mean arterial pressure .