Relationships between brain catecholamine synthesis, pituitary adrenal function and the production of hypertension during prolonged exposure to environmental stress

Male rats were subjected to environmental stresses consisting of flashing lights, audiogenic stimulation and oscillation for 20 weeks on a randomized schedule. The mean systolic blood pressure in the stressed animals rose to 150mm Hg±1.01 by week 8 and ranged between 150 and 160 mm Hg for the remaining 12 weeks, whereas the mean systolic pressure of the non-stressed animals fluctuated between 110 and 120mm Hg throughout this same period of time. Serum corticosterone level in the stressed animals were approximately 3 times higher than controls for the first 4 weeks of exposure; however, by the end of week 5. serum corticosterone declined dramatically in the stressed group and was significantly lower than controls, after which serum corticosterone levels exhibited a cyclic pattern at approximately 6-week intervals. No significant alterations were observed in brain NE and DA and serum FFA throughout the 20-week stress exposure. In a second study, rats received 100 mg kg p.o. ofL-α-methyltyrosine. At the end of weeks 2 and 4, brain NE was depleted by more than 80° in the stressed treated group, whereas brain NE in the non-stressed treated animals was depleted by approximately 45°. indicating a significant increase in the turnover of brain NE The elevated turnover of brain NE returned to control values by the end of the 6th week. In addition, a-MT prevented the stress-induced elevation in systolic blood pressure. These data indicate a close temporal relationship between brain NE synthesis rate and adrenocortical steroid secretion as well as demonstrating that a-MT is an effective antihypertensive agent in stress-induced hypertension.