Aims: 

The enzymes responsible for catecholamine synthesis are tyrosine hydroxylase (TH), dopamine-b-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT). Different stressors variably activate increased synthesis of these enzymes. The present experiment tested the hypothesis that hypergravity (HPG) is a stimulus for catecholaminergic enzymes synthesis in the adrenal medulla (AM), the main source of adrenaline secretion in response to stressful stimuli.

Methods: 

Six groups of 8 male Sprague Dawley rats each were centrifuged at 2G for 0, 6, 24, 72 or 144 hours. Rats were killed by decapitation after the indicated duration of HPG. AM was removed and frozen in liquid nitrogen. mRNA from AM was isolated and quantified by RT-PCR to determine gene expression for TH, DBH and PNMT.

Results: 

mRNA levels for TH and PNMT after 6, 24 or 72 hours of HPG were significantly increased compared with absolute control (p < 0.01). After 144 hours, levels of TH and PNMT mRNA had fallen significantly (p < 0.05) compared to 72 hours and were no longer increased relative to absolute control. DBH mRNA levels were significantly increased after 24 hours HPG (p < 0.05) and 72 hours (p < 0.01) compared with absolute control. After 144 hours, DBH mRNA levels fell and were not significantly different from any of the other four groups.

Conclusion: 

From our results, it is clear that short term HPG was an intensive stressor that activated TH, DBH and PNMT enzyme gene expression in the adrenal medulla. Longer term HPG for 144 hours decreased these enzymes gene expression, suggesting adaptative mechanisms probably involving adrenergic feedback.