Alterations of mouse adrenal medullary catecholamines and enzymes in response to attack: effect of pre- and post-treatment with phenobarbital.

Group-housed male C57BR/cdJ mice (victims) were exposed to attack for 10 min daily for up to 14 days by male Swiss-Webster mice, made aggressive by prolonged isolation. Their adrenal glands were analyzed for tyrosine hydroxylase (TH) and phenylethanolamine-N-methyltransferase (PNMT) activities and for norepinephrine (NE) and epinephrine (EPI) concentrations. TH was increased to 41 per cent above control after two exposures and remained elevated through 14 exposures to attack. PNMT was increased to 29 per cent above control after 2 days and increased further to 50 per cent above control after 14 days of attack. Both NE and EPI increased to 88 per cent and 51 per cent above control, respectively, after 7 days. In victim mice recuperating after 1 week of daily stress, EPI levels and PNMT activities were back to normal after 4 days whereas NE levels and TH activities returned to normal only after 1 week. Phenobarbital (40 mg/kg, i.m.) was effective in preventing the biochemical changes when given 2 h prior to each daily attack but was ineffective when given immediately after each daily stress.