Amino acid gluconeogenesis and glucose turnover in kelp bass (Paralabrax sp.)

The glucose replacement rate, plasma glucose concentration, glucose body mass, and amino acid gluconeogenesis were determined in vivo in fed and fasted kelp bass (Paralabrax clathratus) using [6-3H]glucose administered with [U-14C]glutamate, [U-14C]aspartate, or [U-14C]alanine. Fasting (14 days) and prolonged starvation (72 days) do not produce changes in the replacement rate, body mass, or plasma concentration of glucose. The removal of amino acids from the circulation is rapid in both fed and fasting states with nearly 50% of the administered 14Ctracer disappearing by 5 min. The incorporation of [14C]amino acid carbon into the body glucose mass is also rapid with significant amounts of tracer appearing within 15 min after administration. Gluconeogenesis from alanine and glutamate is increased by fasting whereas that from aspartate is diminished. The gluconeogenic rate is comparable to that previously observed in rats (Dunn, A., M. Chenoweth, and J. G. Hemington. The relationship of adrenal glucocorticoids to transaminase activity and gluconeogenesis in the intact rat. Biochim. Biophys. Acta 237: 192-202, 1971), although the glucose replacement rate is significantly lower. We propose that the paradoxically high rate of gluconeogenesis in fish may serve to provide carbohydrate precursors for mucus synthesis in these carnivorous animals with limited carbohydrate intake.