Hazard/Risk Assessment of Pyridaben: II. Outdoor Aquatic Toxicity Studies and the Water-Effect Ratio

Outdoor acute aquatic toxicity studies with pyridaben and bluegill sunfish (Lepomis macrochirus) and mysid (Mysidopsis bahia) showed that the 96-h LC50s in site-specific water were significantly greater than in classical laboratory studies. In addition, outdoor acute studies showed that pyridaben degrades rapidly in water, in hours, which supports other laboratory and field studies on the fate of pyridaben in aquatic systems. Chronic toxicity to aquatic organisms is not an issue after application in the field because exposures will be brief. The water-effect ratio (WER) of site-specific to laboratory-water 96-h LC50s for L. macrochirus and M. bahia were 18.5 and 24.5, respectively. The lowest WER was used as an application factor with the laboratory LC50 values of several other aquatic organisms to develop adjusted site-specific LC50 values. Comparison of the distribution of adjusted LC50 values with a distribution of potential environmental exposure concentrations for pyridaben in water indicates minimal acute risk to aquatic organisms. When only acute laboratory data are available, the WER approach is a relevant and realistic means for determining an application factor and for estimating the aquatic hazard/risk assessment of non-persistent pesticides, because it considers a host of factors that affect bioavailability and subsequent toxicity.     

Psychosocial effects of jejunoileal bypass for obesity: six-month follow-up.

The authors present the six-month results of a planned five-year follow-up study of 68 patients who underwent jejunoileal bypass for obesity. Eating behaviors changed remarkably, in the direction of conventional eating patterns. Patients generally became more active physically and socially and less embarrassed and socially avoidant. Nearly half showed changes–some better, some worse–in mental status. These changes were not related primarily to operative results, but to a complex set of interpersonal and situational factors.     

Depressor responses to spinal stimulation in the pithed rat

1. Electrical stimulation of the spinal nerves in the pithed rat preparation produces a pressor response due to sympathetic vasoconstriction.2. When the vasoconstrictor effect of sympathetic stimulation is abolished by guanethidine or hexamethonium and the blood pressure is raised by noradrenaline infusion, spinal stimulation produces depressor responses or complex responses containing depressor components.3. Contractions of skeletal muscle caused by stimulation of motor nerves result in complex changes in blood pressure consisting of a pressor component due to clamping of muscle blood vessels and a secondary depressor phase due to functional hyperaemia.4. The depressor response is partly due to stimulation of cholinergic postganglionic fibres. The acetylcholine released, which causes vasodilatation, may be the overflow from neuromuscular junctions or ganglionic synapses.5. Stimulation of the nerves to the adrenal medulla causes release of adrenaline which has a vasodilator effect during noradrenaline infusion.     

Dexamethasone normalizes brain tumor hemodynamics as indicated by dynamic susceptibility contrast MRI perfusion parameters

The purpose of this study is to demonstrate the utility of dynamic susceptibility contrast (DSC) MRI-derived perfusion parameters to characterize the hemodynamic effects of dexamethasone in a 9L gliosarcoma tumor model. Twenty-four rats underwent intracerebral inoculation with 9L tumor cells. Fifteen were treated with a total of 3mg/kg of dexamethasone on days 10-14 post-inoculation, while the remaining 9 rats served as controls. Fourteen days post-inoculation, MRI images, sensitive to total and micro-vascular cerebral blood flow (CBF), mean transit time (MTT), and intravoxel transit time distributions (TTD)s were obtained using a simultaneous gradient-echo(GE)/spin-echo(SE) DSC-MRI method. Dexamethasone-treated animals had a microvascular (SE) tumor CBF that was 45.9% higher (p = 0.0008) and a MTT that was 47.8% lower (p = 0.0005) than untreated animals. With treatment, there was a non-significant 91.3% increase in total (GE) vascular CBF (p = 0.35), and a significant decrease in MTT (49.1%, p = 0.02). The total vascular and microvascular TTDs from the treated tumors were similar to normal brain, unlike the TTDs in the untreated tumors. These findings demonstrate that DSC-MRI perfusion methods can be used to non-invasively detect the morphological and functional changes in tumor vasculature that occur in response to dexamethasone treatment.