Taurine in gerbil retina: changes during ischemia reperfusion/insult (I.R.I.) and aging.

The retina contains a high amount of taurine which suggests a role in retinal function. The mongolian gerbil is well studied in stroke because of its incomplete circle of Willis. Two groups of gerbils were used: one served as control and the other was subjected to unilateral left carotid occlusion during 30 minutes, followed by 60 minutes of reperfusion. Gerbils were selected by ocular fundus and only sensitive gerbils were retained for the experimentation. We studied the level of taurine in gerbil retina of different ages: 3, 9, 15 and 24 months old (sham operated and ischemic groups). Level of taurine was determined by HPLC/electrochemical method. Compared to sham operated groups, level of taurine was significantly increased in ischemic groups for all ages studied. In the sham operated groups, level of taurine was low at birth, reached a plateau, and then decreased with aging. In the ischemic groups, level of taurine regularly increased from 3 to 24 months of age. With comparison evaluated for each age (modification ischemic versus sham operated groups expressed in percentage), level of taurine was quite equal at 3 and 9 months of age, but increased in 15 and 24 months old gerbils.

Effect of piribedil, a D-2 dopaminergic agonist, on dopamine, amino acids, and free radicals in gerbil brain after cerebral ischemia.

The excitatory amino acids (EAA) are involved in the pathogenesis of the cerebral ischemia. Moreover, several investigators have demonstrated that a considerable amount of dopamine (DA) is released in the striatum after ischemia reperfusion/insult (IRI). Recently, studies have demonstrated in vitro, that D-2 agonist, at the level of striatum and retina, may represent a powerful signal to inhibit release of excitatory amino acids implicated in cerebral ischemia. Therefore we have been incited to test, in vivo, the action of a D-2 agonist, piribedil, on gerbil brain after IRI. We have used the Stroke Index (SI); then to precise the mechanism of action, we have determined the levels of dopamine, EAA, and hydroxyl-free radicals (OH), in striatum, hippocampus, and hemisphere. Piribedil, administered at dose of 10 mg/kg, per os, 60 min before induction of transient cerebral ischemia in gerbils, presents a neuroprotective effect, as measured by SI and significantly reverses the increase of DA, EAA, and OH induced by IRI. The mechanism of action of piribedil could be related to its D-2 agonist property.

Effects of Daflon 500 mg* on haemoconcentration and alterations of white blood cell count elicited by the upright position in anaesthetized dogs.

In the passive upright position, arterial and venous pressures in the human feet increase capillary pressure which leads to the filtration of fluid from the circulating plasma into the tissues of the feet. Loss of fluid concentrates both red cells and plasma so that the haematrocrit and plasma protein concentration of venous blood leaving the feet greatly exceed their mean values in the circulation. To study this phenomenon in animals, we used Beagle dogs in upright position. In blood of saphenous vein, red cells, haematocrit and plasma protein concentration have been studied. As in human (Moyses et al. Haemoconcentration and accumulation of white cells in the feet during venous stasis. Int J Microcirc Clin Exp 1987;5:311-20) red cells, haematocrit and plasma protein concentration increase in upright position. The increases in red cells, haematocrit and plasma protein concentration were higher and levels were greater after 2 hours when compared to the corresponding values after 1 hour. Daflon 500 mg, a micronized purified flavonoidic fraction, (200 mg/kg-1 per os) administered 20 minutes before upright position, significantly reduced these increases. This model might be a suitable model to test drugs interfering with venous stasis.

Effect of Daflon 500 mg, a flavonoid drug, on neurological signs, levels of free radicals and electroretinogram in the gerbil after ischemia-reperfusion injury.

The effect of Daflon 500 mg1, purified, micronized flavonoid fraction (90% diosmin, 10% hesperidin) was studied on stroke index, levels of free radicals and electroretinography in the gerbil after ischemia-reperfusion injury. The drug was administered orally at doses of 200, 100 and 50 mg/kg, for 6 days before left carotid occlusion. Daflon 500 mg significantly reversed the increase of stroke index only at the dose of 100 mg/kg and significantly decreased levels of hydroxyl free radicals at all 3 doses with a maximum effectiveness for the dose of 100 mg/kg. Amplitude and latency of the b wave were disturbed after ischemia-reperfusion insult. Daflon 500 mg, 100 mg/kg for 6 days, significantly reversed these modifications. In conclusion, Daflon 500 mg could interact with hydroxyl free radicals, which have a deleterious effect in ischemic tissues, particularly in the retina.

Increase of hydroxyl free radical formation during venous stasis of dogs.

In the passive upright position, arterial and venous pressure in human feet increases capillary pressure, which leads to the filtration of fluid from the circulating plasma into the tissues of the feet. Loss of fluid concentrates both red cells and plasma so that the hematocrit and plasma protein concentration of venous blood leaving the feet greatly exceed their mean values in the circulation. To study this phenomenon in animals, the authors used beagle dogs maintained in an upright position and compared the results to those maintained in a prone position. In the passive upright position, red cell count, hematocrit, and total plasma protein concentrations were significantly increased. Therefore, we have determined the level of hydroxyl free radical formed as assessed by salicylate hydroxylation in the saphenous vein of dogs in an upright and normal position. Hydroxyl free radical formation was significantly higher in the veins of dogs in an upright position than in those in a prone position. The upright position model, which causes increases in hematocrit red cell count and total plasma protein in the saphenous vein, seems suitable for the study of drugs interfering in the pathophysiology of venous stasis. Indeed, the hematocrit increase of red cell count and total plasma protein in the saphenous vein of the beagle is similar to modifications observed in venous blood leaving the human foot after sitting. Moreover, the increase of .OH, concomitant with these modifications, may explain certain pathological observations, for instance, edema. The data clearly suggest that macromolecular extravasculation may be due to tissue injury caused by oxygen free radical formation in the blood vessels.

Free radicals and neurotransmitters in gerbil brain. Influence of age and ischemia reperfusion insult.

In gerbil brain, levels of hydroxyl radicals (OH.) and neurotransmitters such as glutamate, aspartate, GABA (gamma aminobutyric acid) are low at birth, reach a plateau and decrease with age. On the other hand, when gerbils are exposed to an ischemia reperfusion insult (IRI) the older animals have a higher stroke index and hydroxyl radical as well as glutamate and other neuromediators are concomitantly increased. This discrepancy is probably due to differences in the ability of old individuals to respond to oxidative stress. The still incompletely understood relationship between oxidative damage to proteins and accumulation of amino acids, which have an important role as neurotransmitters at physiologic concentrations, but may become neurotoxic at high concentrations, is discussed.

Glutamate accumulation and increased hydroxyl free radical formation in the abdominal aorta and heart of gerbil after ischemia/reperfusion insult.

The concentration of glutamate as well as the hydroxylation of salicylate, as an index of hydroxyl free radical formation, has been determined in the abdominal aorta and heart of gerbils undergoing an ischemia/reperfusion insult (IRI) and compared to control sham-operated gerbils. The amount of glutamate and hydroxylated salicylate (dihydroxybenzoic acid, DHBA) was significantly increased in both the aorta and heart of IRI-treated gerbils as compared to the aorta and in the heart of sham-operated gerbils. Vitamin E (90 mg/kg at 24 and 1 h prior to an IRI) pretreatment prevented the increase of both glutamate and DHBA in both the aorta and heart of IRI-lesioned gerbils. The results suggest that increases in glutamate, perhaps due to the decreased activities of glutamine synthetase, are correlated with increased oxygen free radical formation during an ischemia/reperfusion insult to the heart.

Accumulation of amino acids and hydroxyl free radicals in brain and retina of gerbil after transient ischemia.

The mongolian gerbil was introduced as a stroke model because of its incomplete circle of Willis. Unilateral carotid ligation ischemia produced in such a fashion was not effective in all gerbils. We have selected gerbils by examination of the ocular fundus to study the level of amino acids and hydroxyl free radicals (OH0 formation of DHBA, dihydroxybenzoic acid, from salicylate) in gerbil cerebral ischemia. Only gerbils with absence of retinal blood after ligation were selected as sensitive. One group (sham operated) served as control. The other group was subjected to unilateral left carotid occlusion with a clip during 30 minutes and classified as sensitive and non sensitive. Sixty minutes after release of the clip, levels of aspartate, glutamate, GABA were quantified in left hippocampus and in left retina. Levels of 2,5 DHBA (2,5 dihydroxybenzoic acid) were quantified in left retina and in left hemisphere. Compared to sham operated group, levels of aspartate (greater than 371%), glutamate (greater than 318%), GABA (greater than 122%) and 2,5 DHBA (greater than 385%) significantly increased in the group subjected to carotid occlusion. The determination of concentrations of amino acids and 2,5 DHBA in sensitive gerbils was a suitable method to study cerebral and retinal ischemia.

The auditory evoked potentials of gerbils after temporary occlusion of the left carotid artery.

This study examined brain-stem auditory evoked potentials response (BAEP) changes in the gerbil after temporary occlusion of the left carotid artery. Fourteen adult gerbils were subjected to unilateral left carotid ligation for 30 min. BAEPs were registered before and 5 min after occlusion, then 5 min, 60 min, 120 min, 24 h, 7 days and 28 days after release of the clip. Waves I (cochlear nerve), III (superior olivary complex) and V (inferior colliculus) were examined. Results were analysed using paired Student's t-test. Transient ischaemia increased latencies of waves I, III and V and the changes were more severe 5 min after release of the clip. In the gerbil, BAEPs might be a suitable method to study cerebral ischaemia.