BRAIN PROTEOLYSIS OF OXYTOCIN IN-VITRO AND IN-VIVO CHANGES DURING AGING IN MALE-RATS

Oxytocin proteolysis was studied in vitro with purified synaptic membr anes and in vivo after injection into the hippocampus of male Wistar K yoto rats of different ages. When oxytocin was incubated in vitro with brain synaptic membranes obtained from 2-, 6-, and 12-month-old rats, no difference in the content of C-terminal and N-terminal fragments f ormed by membrane-bound aminopeptidase-like and endopeptidase-like enz ymes, respectively, was found after high performance liquid chromatogr aphy separation and quantification by amino acid analysis. In contrast , the content of all fragments decreased by about 20%-25% when membran es obtained from 18- and 24-month-old rats were used. When [H-3-Tyr(2) ]oxytocin was injected in vivo in the hippocampus of 2-, 6-, 12-, and Is-month-old rats, no difference in the content of free [H-3]-tyrosine and other [H-3]-labelled fragments was found in the hippocampal pepti dic extract after high performance liquid chromatography fractionation . However, the content of air radioactive fragments was about 50% lowe r in the extract from 24-month-old rats. The findings suggest that oxy tocin proteolysis in brain decreases during aging. Such a decrease mig ht counter-balance the impairment of central oxytocinergic transmissio n caused by the age-related decrease of oxytocin content in brain.