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Reduction of cellular energy requirements. Screening for agents that may protect against CNS ischemia
Abstract:
Protection of the brain and spinal cord against ischemia is a goal of vast clinical importance. One approach to this objective is to reduce the tissue's functional activity in order to preserve energy for the metabolic processes that are essential to viability. Experiments to explore ways of reducing function-related energy demands were performed on isolated rabbit retina, a well-characterized model of organized adult mammalian central nervous system (CNS) tissue. The retina was maintained in a nearly physiological state in a miniature "heart-lung" apparatus. Energy metabolism (oxygen consumption and glycolysis) and electrophysiological function (determined by electroretinogram) of the in vitro retina were monitored, and their responses to a series of agents that may reduce energy requirements were determined. Large reversible reductions in O2 consumption, glycolysis, and electrophysiological function were seen in response to mild hypothermia (-3 degrees to -6 degrees C), phenytoin (Dilantin, 100 to 200 mg/kg), chlordiazepoxide (Librium, 200 microM), lithium (1 to 4 mM), Mg++ (6 to 20 mM), strophanthidin (0.15 to 0.25 microM), CO2 (25% to 30%), 2-amino-5-phosphonovaleric acid (APV, 500 microM), amiloride (1 mM), and dantrolene (1 mM). One retina was exposed simultaneously to a combination of six of these agents, which reduced its oxidative and glycolytic metabolism to less than 50% of the control level. The retina recovered metabolic and electrophysiological function after a 2 1/2-hour exposure period. Other agents tested (diphenhydramine, midazolam, nifedipine, nimodipine, and quercetin) had effects on energy metabolism and electrophysiological function that were poorly reversible. Surprisingly little effect was seen in response to general anesthetic agents (thiopental and Althesin) and other CNS depressants (chlorpromazine, ethanol, lidocaine, paraldehyde, valproic acid, and baclofen). The presumed mechanisms through which these agents reduce cellular energy requirements, as well as their potential roles in the treatment of CNS ischemia, are discussed.
Insights
Researchers explored methods to protect the brain and spinal cord from ischemia by reducing tissue activity. Mild hypothermia and specific drugs significantly lowered energy demands and preserved function in rabbit retinas.
Area of Science:
- Neuroscience
- Biochemistry
- Pharmacology
Background:
- Central nervous system (CNS) ischemia poses significant clinical challenges.
- Reducing cellular energy demands is a key strategy for neuroprotection.
- The isolated rabbit retina serves as a model for studying CNS tissue viability.
Purpose of the Study:
- To investigate agents that reduce energy metabolism and preserve function in CNS tissue.
- To evaluate the reversibility of these effects for potential therapeutic applications.
- To identify optimal strategies for mitigating ischemic damage.
Main Methods:
- Utilized an isolated rabbit retina model maintained in a "heart-lung" apparatus.
- Monitored energy metabolism (oxygen consumption, glycolysis) and electrophysiological function (electroretinogram).
- Assessed the impact of various agents and combinations on metabolic and functional parameters.
Main Results:
- Mild hypothermia and agents like phenytoin, chlordiazepoxide, lithium, Mg++, strophanthidin, CO2, APV, amiloride, and dantrolene caused large, reversible reductions in metabolism and function.
- A combination of six agents reduced metabolism to <50% of control, with full recovery after 2.5 hours.
- General anesthetics and other CNS depressants showed minimal, poorly reversible effects.
Conclusions:
- Several agents and mild hypothermia effectively reduce energy demands in CNS tissue.
- These findings suggest potential therapeutic strategies for managing CNS ischemia.
- Further research is warranted to explore the clinical translation of these neuroprotective approaches.