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Utilization of Glutamine in the Developing Rat Jejunum¹

Department of Nutritional Sciences, University of California, Berkeley, CA 94720

The activity of glutaminase was measured in the jejunum of rats during the suckling period. Activity increased significantly (P < 0.05) from 2.37 ± 0.31 mol glutamate/(mg jejunal protein · h) ( ± SD) in the first week to 3.50 ± 0.99 in the second week and 4.75 ± 0.96 during the third week. The quantity of the glutaminase protein, measured with a dot immunobinding assay, remained constant during the first (592 ± 174 cpm bound/g protein) and second (599 ± 125) weeks and then increased significantly by the third week (784 ± 270) after birth. These results indicate that the activity of glutaminase is regulated by alterations in both the quantity and activity of glutaminase protein. The oxidation of [U-¹⁴C]glutamine to ¹⁴CO₂ in vitro also increased during the suckling period, with significantly (P < 0.05) higher rates of oxidation observed by the third week after birth. The capacity of the developing rat jejunum to utilize both glutamine and -hydroxybutyrate (BHB) as fuel sources to support [methyl-³H]thymidine (³HTdR) incorporation was also determined. Addition of glutamine to jejunal homogenates in vitro resulted in a significantly (P > 0.05) higher rate of ³HTdR incorporation than was observed with either glucose or BHB as a fuel source during the early suckling period. In the late suckling period, the addition of BHB and glutamine together resulted in significantly (P > 0.05) higher rates of ³HTdR incorporation than that found with glucose as a fuel source. These data suggest that both glutamine and BHB are important fuel sources in the jejunum during the suckling period.

KEY WORDS: • glutaminase • intestine • development • fuel utilization

¹ This work was supported in part by a National Institutes of Health Training Grant.

² To whom reprint requests should be addressed.

Manuscript received 25 February 1987. Revision accepted 27 October 1987.