The rapid activation of tyrosine hydroxylase by the subcutaneous injection of formaldehyde

Ten minutes following the subcutaneous injection of formaldehyde, there is a 2-fold activation of adrenal medulla tyrosine hydroxylase. Enzyme activation appears to involve a shift of a fraction of the low affinity form of the enzyme to a higher affinity form. In the nonstessed rat approximately 29% of adrenal TH is in the activated (low Km) form. Following formaldehyde injection, approximately 54% of the enzyme is in the activated (low Km) form. The addition of cyclic AMP, ATP and Mg⁺⁺, in the presence of endogenous cyclic AMP-dependent protein kinase, to the enzyme obtained from adrenals of either the stressed or nonstressed rats increased the activity of both enzyme preparations to the same level. These data indicate that acute stress activates adrenal tyrosine hydroxylase in the rat and that a cyclic AMP-dependent protein phosphorylating system mediates the activation.