Temperature effects on catecholamine accumulation in neuronal and extraneuronal compartments in the cod spleen

The effects of temperature on the accumulation of radiolabelled adrenaline and noradrenaline were studied in the perfused spleen of the Atlantic cod, Gadus morhua. A decrease in temperature from 20-24 to 10 degrees C showed a corresponding decrease in the neuronal and extraneuronal accumulation of both adrenaline and noradrenaline. The Q10-values for the neuronal accumulation of adrenaline and noradrenaline were 3.6 and 2.1, respectively. This indicates that adrenaline is accumulated neuronally by an active process. An increased perfusing time resulted in an even more pronounced difference in the neuronal accumulation between the two amines. The extraneuronal accumulation of both amines was only slightly affected by a 10 degree C decrease in temperature, and with increasing perfusion time, the accumulation increased as in a passive diffussion. There are strong indications that adrenaline and noradrenaline not only accumulate differently from each other in the adrenergic neurons of the cod spleen, but also that the adrenaline uptake mechanism neuronally might resemble the characteristic mammalian catecholamine uptake while noradrenaline seems to accumulate by a more primitive mechanism, not sensitive to a reduction in temperature. This might be physiologically important for the cod, since the spleen can synthetize adrenaline from noradrenaline and the uptake of adrenaline from the circulation is therefore less important.