Blood amino acid studies. II. Effects of dietary lysine concentration, sex, and growth rate on plasma free lysine and threonine levels in the rat

Morrison, A.B.; Middleton, E.J.; Mclaughlan, J.M.

Canadian Journal of Biochemistry and Physiology 39: 1675-1680


PMID: 14476284
Accession: 013971256

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Groups of 6 male and 6 female weanling rats received a basal lysine-deficient diet alone or with different amounts of lysine. After an initial lag, free lysine levels in plasma rose rapidly, to a maximum of 130 micro g per ml in males, and 171 micro g per ml in females, when the diet contained about 1.0% lysine. Both sexes showed maximum growth when the diet contained 0.8% lysine. Groups of 6 male rats received the basal diet containing 20% maize oil or rapeseed oil, alone or with lysine. The maximum growth rate of rats given rapeseed oil was about 35% less than of those on maize oil, but there was no effect on the amount of lysine required to produce maximum free lysine values in plasma or maximum growth. Rats on rapeseed oil had a much lower maximum plasma lysine level than those on maize oil. Free threonine levels in plasma showed a reciprocal relation with those for lysine. At levels of lysine intake below 0.72%, plasma threonine levels were much lower in rats on rapeseed oil. The free lysine level obtained when growth was highest was about 90 micro g per ml. The ratio between free lysine and threonine in plasma may indicate the adequacy of the diet lysine content.