Brain proteolysis of oxytocin in vitro and in vivo changes during aging in male rats.
Oxytocin proteolysis was studied in vitro with purified synaptic membranes and in vivo after injection into the hippocampus of male Wistar Kyoto 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 formed by membrane-bound aminopeptidase-like and endopeptidase-like enzymes, respectively, was found after high performance liquid chromatography separation and quantification by amino acid analysis. In contrast, the content of all fragments decreased by about 20%-25% when membranes obtained from 18- and 24-month-old rats were used. When [3H-Tyr2]oxytocin was injected in vivo in the hippocampus of 2-, 6-, 12-, and 18-month-old rats, no difference in the content of free [3H]-tyrosine and other [3H]-labelled fragments was found in the hippocampal peptidic extract after high performance liquid chromatography fractionation. However, the content of all radioactive fragments was about 50% lower in the extract from 24-month-old rats. The findings suggest that oxytocin proteolysis in brain decreases during aging. Such a decrease might counterbalance the impairment of central oxytocinergic transmission caused by the age-related decrease of oxytocin content in brain.
Bernard B. Brodie Department of Neuroscience, University of Cagliari, Italy.
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Stancampiano
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Melis
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Fratta
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Argiolas
D000375:Aging / Q000378:metabolism*; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D006624:Hippocampus / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D008969:Molecular Sequence Data; D010121:Oxytocin / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D051381:Rats; D011921:Rats, Inbred WKY; D013570:Synaptic Membranes / Q000378:metabolism
D000596:Amino Acids; D010446:Peptide Fragments; D010121:Oxytocin