Influence of aging and drug treatment on the bioenergetics of hypoxic brain.

Synaptosomes isolated from the forebrain of rats of different ages (20, 60 and 100 weeks of age) were incubated in Krebs-Henseleit-Hepes (pH 7.4) buffer, for 10 min at 24 degrees C. The energetic state was defined by the redox state of the intramitochondrial NAD-couple (delta Gox-red) and the phosphorylation state of adenine nucleotide system (delta GATP). The biological energy "lost" by the system during the coupled reactions was estimated by the delta delta G = delta Gox-red - delta GATP. The animals were submitted for 10 min to different degrees of in vivo hypoxia. To elucidate the mechanism of action, the effect of the pretreatment with drugs acting on oxygen availability (almitrine) or on microcirculation and metabolism (delta-yohimbine) was tested. In synaptosomes isolated from the forebrain of animals submitted to moderate degree of hypoxia (oxygen arterial partial pressure ranging between 32 and 29 mmHg) the efficiency of the system was quite similar to that observed in normoxia, with the exception of the older rats. In synaptosomes isolated from the forebrain of rats submitted to severe degree of hypoxia (oxygen arterial partial pressure ranging between 20 and 18 mmHg) the efficiency of the system was markedly altered as a function of both aging and severity of hypoxemia. The pretreatment with the agent increasing the oxygen availability partially modified the efficiency of the system, the alpha-blocking agent being less important. The drug action was markedly related to both the age and the degree of hypoxia.