Contribution of adrenal medulla, spleen and lymph, to the plasma levels of dopamine β-hydroxylase and catecholamines induced by hemorrhagic hypotension in the dogs

Controlled hemorrhagic-hypotension in pentobarbital anesthetized dogs causes progressive increases in dopamine β-hydroxylase (DBH) and catecholamine (CA) aortic-plasma levels. The total plasma content of DBH increased by nearly 1100 U (controls: 2521 ± 304 U; 75 min of hemorrhage: 3684 ±379 U). This was related to a greater adrenal discharge of both CA and DBH. Nearly 24 U/ml of DBH and 0.7 μg/ml of CA were present in the left lumbo-adrenal vein during the bleeding period. During this phase, the plasma flow in the left lumbo-adrenal vein was reduced from 0.093 ± 0.020 to 0.032 ± 0.010 ml/kg/min and the output of DBH was 7.05 ± 1.90 U/min. Approximately 600 U of DBH activity were released by the left adrenal during the 75 min. of hemorrhagic-hypotension. The output of DBH and CA was also recorded from the spleen and the thoracic duct. No significant aorto-splenic (arterial-venous) differences for DBH and CA were observed during the hemorrhagic period. The lymph DBH and CA concentrations increased during the bleeding phase, from 25.1 ± 1.6 U/ml to 41.4 ± 6.7 U/ml and from 5.2 ± 1.6 ng/ml to 205 ± 15 ng/ml, respectively. However, due to the reduction (48%) in lymph flow, there was no change in the output of DBH via the lymph. These results indicate that the adrenal glands contribute almost exclusively to the increase in plasma DBH and CA induced by hemorrhagic-hypotension in dogs. The infusion of the reservoir blood with a lower DBH and CA content than the one present in the animal at the time produced a rapid fall in circulating CA levels and no change in the DBH concentration. A 25% increase in the calculated total plasma content of DBH occurred the transfusion (3684 ± 379 U to 4301 ± 448 U). With blood volume restoration, the output of DBH and CA from the left adrenal gradually fell to prehemorrhage levels and no aorto-splenic arteriovenous differences were observed after transfusion. However, a marked increase in lymph DBH output was observed (1500 U in 60 min). This effect was due to augmented lymph flow (3-fold) and a persisting elevated lymph enzyme concentration. The results suggest that the maintenance of elevated circulating DBH levels and the increase in the plasma enzyme content with blood reinfusion, are related to a greater circulation. It was demonstrated that changes in circulating DBH could occur after stress cessation and are possibly related to a greater rate of interstitial fluid formation with the resultant increase in lymph enzyme output.