Abstract
1. The effects of reserpine and exposure to a stressing atmosphere containing 20% CO2 for 5 hr on catecholamine (CA) levels and dopamine beta-hydroxylase (DBH) activity of adrenal, spleen and plasma of cat, rabbit, rat and guinea-pig were studied. 2. Twenty-four hr after an I.P. injection of reserpine, the CA contents of the adrenals and spleens were markedly reduced in all the four species studied. Adrenal and splenic DBH activity was unchanged in reserpine treated cats and rats. The enzyme activity decreased by 28 and 36% in adrenals of rabbits and guinea-pigs, and a 33% diminution was observed in the spleens of both species. 3. A marked rise in guinea-pig plasma DBH activity was obtained 24 hr after reserpine, while plasma DBH activity was unchanged in the rat. 4. Exposure of rats to a stressing atmosphere containing 20% CO2 for 5 hr increased the circulating noradrenaline (NA) levels by 600%, but plasma DBH activity remained unchanged. CO2 exposure caused both, an increase in plasm NA levels and DBH activity in the guinea-pig (950% and 100%, respectively). 5. The combined treatment with reserpine plus immediate exposure to CO2 produced a 230% rise in rat plasma NA with no concomitant change in DBH activity. A similar treatment caused a 75% fall of NA levels and an increase in DBH activity of 600% in the guinea-pig. 6. The ratios of total DBH activity to CA in the spleen and adrenal were much higher in the guinea-pig than in the rat. The fraction of the total DBH activity that can be solubilized by osmotic shock of purified adrenomedullary chromaffin granules was 28% in the rat and 71% in the guinea-pig. If one makes the assumption that 'soluble' and 'releasable' DBH may be equated, the amount of 'releasable' DBH into the circulation is much greater in the guinea-pig than in the rat. 7. The results suggest that the guinea-pig is a better model than the rat to study circulating DBH activity as an index of exocytotic CA release from adrenergic neurones and adrenal medulla, and therefore of sympathetic activity. The results also indicate that previous data trying to correlate sympathetic activity with circulating DBH activity carried out in the rat have to be reconsidered in the light of data obtained in the guinea-pig.
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