Chronic Physical Stress Changes Gene Expression of Catecholamine Biosynthetic Enzymes in the Adrenal Medulla of Adult Rats

In this study we examined how chronic forced running (CFR) affects the expression of catecholamine biosynthetic enzymes and cAMP response element-binding (CREB) in the adrenal medulla and the weight of adrenal glands of rats. Also, we examined how CFR and additional acute immobilization stress affect the expression of catecholamine biosynthetic enzymes in the adrenal medulla and the concentration of catecholamines and corticosterone (CORT) in the blood plasma. In this experiment we used as a model forced exercise in rats (treadmill running). We used the most advanced method for determining the level of gene expression, Real-time PCR with TaqMan probes, as well as Western blot analysis (ECL). We found that CFR decreases tyrosine hydroxylase (TH), and dopamine-hydroxylase (DBH) mRNA and protein levels in the adrenal medulla. The decreased TH and DBH mRNA levels coincide with the reduced expression of CREB in the adrenal medulla and with the reduced plasma CORT level. Additionally, CFR reduces the level of phenylethanolamine N-methyltransferase (PNMT) mRNA, but elevates its protein level in the adrenal medulla and increases the concentration of adrenaline (A) in the plasma. Reduced level of PNMT mRNA in the adrenal medulla coincides with reduced plasma CORT level. The additional acute immobilization stress increases gene expression of catecholamine biosynthetic enzymes in the adrenal medulla, as well as catecholamines and CORT levels in the plasma. The increased synthesis of PNMT enzyme in the adrenal medulla may result in an increased biosynthesis of A under chronic stress conditions. Additionally, increased level of catecholamines in the plasma after chronic physical stress is the allostatic load that may induce numerous diseases and pathological conditions.