Different effects of hypothermia on amino acid incorporation and on amino acid uptake in the brain in vivo.

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 using 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 degree 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.