Regulation of Tyrosine Hydroxylase and Dopamine β‐Hydroxylase mRNA Levels in Rat Adrenals by a Single and Repeated Immobilization Stress

Adrenal catecholamines are known to mediate many of the physiological consequences of the “fight or flight” response to stress. However, the mechanisms by which the long‐term responses to repeated stress are mediated are less well understood and possibly involve alterations in gene expression. In this study the effects of a single and repeated immobilization stress on mRNA levels of the adrenal catecholamine biosynthetic enzymes, tyrosine hydroxylase and dopamine β ‐hydroxylase, were examined. A repeated 2‐hr daily immobilization for 7 consecutive days markedly elevated both tyrosine hydroxylase and dopamine β ‐hydroxylase mRNA levels (about six‐ and fourfold, respectively). In contrast, tyrosine hydroxylase but not dopamine β ‐hydroxylase mRNA levels were elevated immediately following a single immobilization. The elevation in tyrosine hydroxylase mRNA with a single immobilization was as high as with seven daily repeated immobilizations. This elevation was not sustained and returned toward control values 24 hr later. Both tyrosine hydroxylase and dopamine β ‐hydroxylase mRNA levels were elevated immediately following two daily immobilizations to levels similar to those observed after seven immobilizations and were maintained 24 hr later. The results indicate that both tyrosine hydroxylase and dopamine β ‐hydroxylase mRNA levels are elevated by stress; however, the mechanism and/or timing of their regulation are not identical.