DBH inhibitory factors of brain tissue

In vivo turnover of NA in the brain is considerably high, but in vitro only a low activity of the enzyme DBH is detectable. It is supposed that this effect is brought about by endogenous enzyme inhibitors. It was demonstrated that the addition of rat brain homogenate, as well as different subcellular fractions from rat brain, inhibit the human serum DBH. Inhibitory activity is resistant to heat and acid but does not seem to be uniformly distributed within the cell. Pretreatment of brain homogenate with pronase reduced its inhibitory activity. In conclusion, pronase sensitive peptides are partially responsible for the inhibitory potency of tissue homogenates.