Evolution in vivo of the synthesis rate of catecholamines in various peripheral organs of the rat during cold exposure.

The synthesis of catecholamines (CA) has been studied in the heart, spleen, submaxillary glands and adrenals of rats exposed to 4 degrees C for 2.5, 24 or 48 h. The synthesis rate has been estimated 30 min after an i.v. injection of 3H tyrosine (TY) by the evaluation of the ratio: 3H-CA specific activity/3H-TY specific activity. In the sub-maxillary glands, cold exposure reduced the noradrenaline (NA) synthesis by 40% at times 24 and 48 h. In the spleen, NA synthesis was multiplied by a factor 1.6 at times 2.5 and 24 h and 2.8 at time 48 h. In the heart, it was increased by a factor 1.3 after 2.5 h, 2.8 after 24 h and 5.5 after 48 h: an important fall in cardiac NA level was observed during the first 24 h of cold exposure indicating that the synthesis capability was unsufficient to compensate the cold-induced NA release. In the adrenals, adrenaline + NA synthesis was not significantly enhanced during the first 24 h of cold exposure and increased by a factor 2.4 at time 48 h. The important increases in CA synthesis which are observed during the 24-48 h interval are likely consecutive to the induction of tyrosine hydroxylase which has been reported in the rat exposed to cold.