DIFFERENT EFFECTS OF HYPOTHERMIA ON AMINO-ACID-INCORPORATION AND ON AMINO-ACID-UPTAKE IN THE BRAIN INVIVO

The temperature dependence of the incorporation of amino acids into cerebral proteins and that of the transport of amino acids through the blood-brain barrier were studied. We measured the protein synthesis rate in vivo over a wide temperature range (14-degrees-C-38-degrees-C) in male Sprague-Dawley rats u sing a flooding dose of labeled valine. There was a linear dependence of the protein synthesis rate on temperature. The temperature quotient expressed as per cent decrease per 1-degrees-C was somewhat lower at the lower temperatures, a decrease from 7.8% in the 37.7-32.5-degrees-C range to 6.7% in the 25.5-14-degrees-C range. The transport of the three amino acids phenylalanine, lysine, and alanine, representing three transport systems, through the blood-brain barrier showed no temperature dependence in vivo. The results show that in hypothermia cerebral metabolic rates are lowered to a great extent, while some aspects of metabolic transport are not affected.