Effects of handling, decapitation, anesthesia, and surgery on plasma noradrenaline levels in the white rat

Abstract

To determine the normal resting level of plasma noradrenaline [norepinephrine] (NA) in unanesthetized and undisturbed white rats, 20 warm-acclimated rats previously fed a semisynthetic diet were implanted with an intraaortic cannula and allowed to recover for a period of 5 days. They were then placed in a closed metabolism chamber after fitting an extension to the cannula which allowed blood sampling in animals which were unrestriced and unaware of the procedure. The average NA concentration in the plasma was 0.15 .+-. 0.01 ng/ml as measured by a radioenzymatic method based on formation of [methyl-3H]adrenaline. Levels of noradrenaline in nanograms per milliliter measured in groups of 4-5 rats after various treatments were as follows: manipulation, 0.63 .+-. 0.18; decapitation, 1.32 .+-. 0.25; 5 min after 3% halothane, 0.23 .+-. 0.01; decapitation under halothane, 0.40 .+-. 0.03. In 5 rats fed Purina laboratory chow at room temperature, values were 0.11 .+-. 0.02 ng/ml and concentration invariably increased after manipulation and after decapitation. The elevated plasma NA concentration in rats cannulated under halothane anesthesia dropped to normal levels in less than 1 h after recovery from anesthesia, thus indicating that tissue trauma associated with cannula implantation does not have a long-lasting effect on plasma NA levels. These results show that special precautions must be taken to ensure minimal sympathetic activity when resting plasma NA levels are to be measured and that data on the effect of various treatments on peripheral levels of NA based on use of anesthetized, manipulated, or decapitated rats are of doubtful significance as use of these procedures result in abnormally high levels of NA in the control animals used for comparison.