Carnosine Synthesis in Olfactory Tissue During Ontogeny: Effect of Exogenous ?-Alanine

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Abstract
Carnosine is present in rat olfactory mucosa on day 16 of gestation. The tissue content of this dipeptide increases progressively during fetal and postnatal life. Radioactive carnosine can be isolated from cultured embryonic rat olfactory mucosa incubated with [14C].beta.-alanine as early as 13-14 days of gestation. The amount of incorporation also increases progressively with the initial age of the explant and with time in culture indicating in vitro maturation of the carnosine synthesis capability of olfactory tissue. To test whether the level of .beta.-alanine was limiting the synthesis of carnosine, the effect of elevated .beta.-alanine levels on tissue carnosine content was evaluated. Exogenous .beta.-alanine caused an increase in the tissue content of carnosine at several ages in vivo and in vitro in adult animals this increase was observed in olfactory bulb, olfactory mucosa and skeletal muscle. There was no associated alteration in carnosine synthetase activity. The different half-lives of carnosine in olfactory tissue and muscle seemed unaltered, arguing against any effect on degradative enzymes. Thus, tissue carnosine levels are regulated, at least in part, by substrate availability. The early appearance of carnosine synthetic capacity during prenatal development indicates that this enzyme activity should be a valuable aid in studying early events in olfactory neuron maturation.