Effect of alpha-trinositol on carrageenan-induced rat paw edema and lowering of interstitial fluid pressure.

Alpha-trinositol attenuates edema formation and capillary albumin extravasation and lowering of interstitial fluid pressure (Pif) in several acute inflammatory reactions in rat skin or trachea. The lowering of Pif is an important driving force required to explain the rapid edema formation in acute inflammatory reactions. The lowering of Pif and edema formation are attenuated by alpha-trinositol, which is suggested to act on the cellular adhesion receptor for extracellular matrix components. This would represent a novel therapeutic strategy for acute inflammation. To further clarify the mechanisms behind the anti-inflammatory effects of alpha-trinositol, the effects of pre- and post-treatment with alpha-trinositol on edema formation and lowering of Pif were studied after subdermal injection of carrageenan in the rat. The experiments measuring Pif showed that the lowering of Pif induced by carrageenan was abolished by 10 mg alpha-trinositol when administered either prior to or after injection of 5 microl 1% (w/v) lambda carrageenan in the dorsum of the paw. Edema formation after injection of lambda carrageenan (100 microl, 1.5% w/v) into the foot pad was studied in a separate series. In control animals receiving saline vehicle, the volume of the paw injected with carrageenan increased by approximately 30% after 3-4 h. The only significant effect of infusion of 20 mg kg(-1) h(-1) alpha-trinositol was a reduction of edema to approximately 20% when treatment was started 1 h before carrageenan injection. Therefore, the plasma concentration of alpha-trinositol must already be high when carrageenan is injected in order to prevent edema in the late phase. In conclusion, the present results indicate that the mechanisms involved in the lowering of Pif in the early phase of edema development are different from those responsible for the manifest edema measured 3-4 h after carrageenan.

The effect of alpha-trinositol on cholera toxin-induced fluid accumulation in pig (Sus scrofa domesticus) jejunum in vivo.

The effect of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate) on cholera toxin-induced fluid accumulation (i.e., net fluid secretion) was studied in the pig jejunum in vivo. Cholera toxin caused a dose-dependent fluid accumulation in control experiments. Intravenous injection of alpha-trinositol produced a reduction of the response to cholera toxin with a significant maximal inhibition of 36%. However, in high concentrations of alpha-trinositol this inhibition was absent.

The effect of alpha-trinositol on cholera toxin-induced hypersecretion and morphological changes in pig jejunum.

alpha-Trinositol (D-myo-inositol 1,2,6-trisphosphate, PP56) is a novel antiinflammatory drug. This study elucidates the effect of intravenous alpha-trinositol on basal and acute fluid transport and morphological changes following cholera toxin administration in pig jejunum in vivo. Using isolated jejunal tied-off loops, the fluid hypersecretory (accumulation) effect of different doses of cholera toxin was studied in pigs treated intravenously with saline added different doses (0, 4, 8, 16 and 32 mg x kg-1 x hr-1) of alpha-trinositol. Levels of alpha-trinositol, as well as stereomicroscopical, light microscopical and scanning electron microscopical morphological studies were performed. Cholera toxin evoked a dose-dependent fluid hypersecretion. Treatment with alpha-trinositol caused a dose-dependent inhibition of the cholera toxin-induced fluid hypersecretion and did not affect basal fluid absorption. The 16 mg x kg-1 x hr-1 alpha-trinositol dose gave a maximal inhibition of 36%. Morphological studies showed only minor changes following 6 hr of exposure to 20 micrograms x loop-1 cholera toxin. These changes consisted of dilation of the villus capillaries, an increase of apical membrane blebbing and a reduction of the intercellular space. Treatment with 16 mg x kg-1 x hr-1 alpha-trinositol alone did not induce any morphological changes, and did not alter the morphological changes induced by cholera toxin, which caused fluid hypersecretion and only minor acute morphological changes. In conclusion, alpha-trinositol treatment reduced cholera toxin-induced fluid hypersecretion without altering basal fluid absorption, basal morphology, or cholera toxin-induced morphological changes in pig jejunum in vivo.

Effects of ischemia on regional ligand binding to adrenoceptors in the rat brain.

Changes in ligand binding to adrenoceptors ([3H]prazosin to alpha 1-receptors, [3H]idazoxan to alpha 2-receptors and [125I]cyanopindolol to beta-receptors) following transient cerebral ischemia were investigated using autoradiographic methods. The binding was quantified in brain sections from control rats, rats subjected to 15 min of 2-vessel occlusion ischemia, and rats with recirculation times of 1 h, 1 week or 4 weeks after ischemia. No significant change in alpha 1-receptor binding was observed during and immediately following ischemia, but a decrease was noted in the vulnerable hippocampal CA1 region following 1 week's survival. In the parietal cortex, the ligand binding to alpha 1-receptors increased at 4 weeks. A reduced [3H]idazoxan binding was observed 1 h after ischemia in the temporal cortex and amygdala. No change in ligand binding to beta-receptors was seen in the early phase postischemia, but a marked increase had occurred in the hippocampal CA1 region at 1 and 4 weeks after ischemia (+163% and +142%, respectively), presumably due to accumulation of macrophages expressing beta-receptors. The early postischemic changes in receptor binding may represent downregulation of the adrenoceptors by processes activated during ischemia, while neuronal degeneration, compensatory mechanisms in surviving neurons and proliferation of non-neuronal cells may account for the subsequent changes.

Extracellular brain cortical levels of noradrenaline in ischemia: effects of desipramine and postischemic administration of idazoxan.

Using microdialysis, extracellular noradrenaline (NA) levels in the rat cerebral cortex were studied under isoflurane/N2O anaesthesia before, during and for 6 hours following 10 min of forebrain ischemia in a 2-vessel occlusion model. A microdialysis probe was introduced into the parietal cortex and dorsal hippocampus in anaesthetized rats and continuously perfused with Krebs-Ringer-bicarbonate buffer with or without the NA uptake inhibitor desipramine (DMI, 5 microM). Twenty min fractions were collected and the extracellular NA levels were measured in the dialysates using HPLC with electrochemical detection. The basal NA concentration in the dialysate was 10.5 +/- 1.8 (mean +/- SEM) pg/20 min fraction and increased to 39.3 +/- 4.8 pg/20 min fraction after local administration of DMI. During ischemia, NA increased to 38 times the basal level without DMI, and 6 times with DMI included during two hours' perfusion prior to ischemia. After recirculation NA levels returned to, or even transiently decreased below, preischemic values. With DMI present in the dialysis buffer, administration of idazoxan immediately following ischemia delayed the return to preischemic NA levels in the recirculation phase. In the absence of DMI, no effect of idazoxan on postischemic levels of NA was found. Local administration of DMI increases basal extracellular NA levels and reduces the ischemia-induced NA release. The latter effect may be a due to inhibition of the NA uptake system working in a reversed mode, or as a result of decreased synthesis of NA due to activation of presynaptic alpha 2-receptors by the increased synaptic NA levels. Postischemic treatment with the alpha 2-adrenoceptor antagonist idazoxan in combination with DMI prolongs the period of elevated extracellular NA levels, which may be of importance for the protective properties of idazoxan against ischemic cell injury.