Post-ischemia ERG recovery is influenced by temperature.

In experimental work on retinal ischemia and its medical management, we have been disturbed by the large variations in the electroetinogram (ERG) recovery of rabbit eyes subjected to similar degrees of ischemia. We investigated whether body temperature might be one of the critical factors. We studied pigmented Dutch rabbits that had been subjected to 60 min of ocular ischemia followed by 4 h of reperfusion at different body temperatures. Ischemia was produced by cannulating the anterior chamber and raising the intraocular pressure. Scotopic ERGs and rectal temperatures were recorded at regular intervals. Rabbits with a subnormal mean temperature of 35.5-37.7 degrees C throughout the experiment showed mean a- and b-wave recoveries of 131.52% and 107.68% of preischemic values after 4 h reperfusion. At temperatures between 37.8-38.9 degrees C, the a- and b-waves only recovered to 88.43% and 32.0% respectively. Even small degrees of cooling greatly enhanced post-ischemic ERG recovery. This may explain some of the variations in ERG recovery that have been reported in the literature. We suggest that body temperature should be tightly controlled between 37.8 and 38.9 degrees C during ischemia experiments to stabilize results and minimize errors in judging therapeutic effects. Retinal cooling may be a means to protect the retina against ischemic damage in clinical situations.

Electroretinogram recovery in the rabbit after repetitive short-term ischemia in light and dark.

PURPOSE: To determine the time course and reproducibility of electroretinogram recovery after short-term (5- to 20-minute) retinal ischemia in the light and in the dark. METHODS: Electroretinogram recovery was measured in Dutch rabbits after 5-, 10-, or 20-minute episodes of ocular ischemia, repeated three times at 1-hour intervals. Results were compared under light- and dark-adapted conditions. RESULTS: The rate of b-wave recovery was highly reproducible after repetitive ischemic insults in the same eye. The rate of b-wave recovery varied in proportion to the duration of ischemia but generally reached 100% of preischemic levels within 45 to 60 minutes. Recovery was slower under dark-adapted conditions than under light-adapted conditions, and 10 minutes of ischemia appeared to be a critical duration to maximize light- and dark-adapted metabolic differences. CONCLUSIONS: Because of the speed and reproducibility of electroretinogram recovery, the use of short-term ischemic episodes may facilitate studies on the pharmacologic therapy of retinal ischemia. It remains to be determined, however, whether the retinal effects of short-term ischemia are mediated by the same mechanisms as the effects of longer-term ischemia.

Protection of rabbit retina from ischemic injury by superoxide dismutase and catalase.

PURPOSE: To provide evidence that free radical damage is a component of postischemic retinal injury; to determine whether antioxidant enzymes, superoxide dismutase (SOD) and catalase, can protect the retina from ischemic injury. METHODS: Total retinal ischemia for 60 or 75 min was produced in Dutch rabbits by raising intraocular pressure. Retinal recovery was monitored with the electroretinogram. Enzymes were administered as an intravenous bolus dose 2-3 min before restoration of circulation. RESULTS: In eyes subjected to 60 min ischemia, the amplitude of the a-wave 4 hours after reperfusion averaged 114.9% of baseline value in control rabbits and 126.5% in SOD-treated animals. The b-wave amplitude at this time was 79.3% and 106.8% in control rabbits and SOD-treated rabbits, respectively. After an ischemic insult of 75 min, at 4 hours the a-wave amplitude was 89.2% of baseline in control eyes, 108.8% in SOD-treated eyes, 159.6% in eyes that received a combination of SOD and catalase, and 149.8% in catalase-treated eyes. The amplitude of the b-wave was reduced to 47.8% in control eyes and 44.8% in SOD-treated eyes, but recovered to 92.3% in rabbits that received the combination therapy and 98.8% in animals that received catalase alone. CONCLUSIONS: These findings suggest that free radical generation is involved in ischemic tissue damage. The fact that antioxidant enzymes can be protective has implications for the treatment of acute ischemic diseases of the retina.

Effect of LH, FSH, LH + FSH and homoplastic pituitary extract on developing testis and epididymis of pigeon Columba livia.

Ovine LH is needed for differentiation of juvenile Leydig cells and for their maintenance and steroidogenic potential, while FSH is necessary for Sertoli cell activity and spermatogonial multiplication suggesting that LH is steroidogenic hormone and FSH is gametogenic in the developing pigeon, C. livia. Homoplastic pituitary extract is more potent than ovine LH + FSH in stimulating gametogenic and endocrine components of the developing testis.