Dopamine-beta-hydroxylase activity in plasma, spleen and adrenal gland of streptozotocin-diabetic rats: correlation with cataracts.

In streptozotocin-diabetic rats a large increase in plasma dopamine-beta-hydroxylase activity was observed. This increase returned to control values with sufficient insulin doses (6 I.U/day); lower insulin doses did not allow normal level to be reached, a dose-dependent decrease being observed. Although the glycemia levels in the diabetic state are responsible for the plasma dopamine-beta-hydroxylase, there is no exact ratio between these two parameters when diabetic animals are treated with different insulin doses which suggests not only the clearance of plasmatic dopamine-beta-hydroxylase, but a contribution from exocytotic tissues as well. In the experimental conditions, before cataracts appeared, the animals about to develop opaque lenses showed a greater dopamine-beta-hydroxylase activity than those which were to remain without this complication. After three months in diabetic state, the severity of disease was evident in the animals with cataracts since they showed a significantly higher function of the sympathoadrenal axis, expressed in spleen and adrenal dopamine-beta-hydroxylase activity. Plasma dopamine-beta-hydroxylase, as a minority glycoprotein can be considered a useful parameter of other mannose-terminal glycoproteins without having a well-known function, and also as a high risk protein, the accumulation of which in several places contributes to the complex pathogenic mechanism of diabetes complications.