Adrenal origin of the increase in plasma dopamine β-hydroxylase and catecholamines induced by hemorrhagic hypotension in dogs

Controlled hemorrhagic hypotension in anesthetized dogs causes progressive increases in dopamine β-hydroxylase (DBH) and catecholamine (CA) plasma levels and in heart rate. The concentration (units per milliliter) and the calculated total plasma content of DBH activity [(units) circulating + reservoir + samples] increased 2.6 and 2.3 times, respectively. A significant positive correlation (P<0.001) was found between the plasma levels of DBH and CA; however, the CA plasma levels increased earlier and were of greater magnitude (10-fold) than those of DBH. These results suggest that CAs are more sensitive indicators of acute changes in adrenergic activity than DBH. Surgical bilateral adrenalectomy completely abolished the increases in circulating CA and DBH levels and in heart rate induced by the hemorrhage, independently of the percentage of blood removed. These results indicate that the adrenal glands contribute almost exclusively to the rise in plasma DBH and CA caused by the bleeding stress and that high circulating CA concentrations seem to account for the tachycardia that accompanies the hemorrhagic hypotension. The infusion of the reservoir blood with a lower DBH and CA content than that present in the animal at that time produced a rapid fall in circulating CA levels (59.2 ± 8.9 to 10.8 ± 3.3 ng/ml) and no change in the DBH concentration (5.43 ± 0.42 and 5.40 ± 0.53 U/ml). A 38% increase in the calculated total plasma content of DBH occurred with the transfusion. Due to the large size of the DBH molecules trapping in tissues during the hemorrhagic hypotension period might have occurred. The improvement in the hemodynamic conditions caused by the transfusion would facilitate the washout of the enzyme from the tissues into the circulation.