Increased adrenal epinephrine and norepinephrine in spontaneously hypertensive rats treated with hyperbaric oxygen

Adrenal catecholamines were determined in Wistar Kyoto rats (WKY), and stroke-prone and stroke-resistant spontaneously hypertensive rats (SHRSP, SHR) treated with hyperbaric oxygen for 90 minutes daily from 6 to 13 weeks of age. The animals were divided into 5 groups. Group I (control group), was handled under the same conditions as pressure-treated groups II and III, but with ambient oxygen pressure and concentration. Group II (pressure-control group), was treated with 2 atmospheric absolute pressures (ATA) of air without any oxygen provided. Group III (high-oxygen group), was exposed to 2 ATA under the environment of air saturating oxygen. Group IV (antihypertensive group), was treated with hydralazine. Group V (adrenalectomized group), was given 1% NaCl solution and bilateral adrenalectomy. The average contents of adrenal norepinephrine of SHR and of SHRSP in Group I were greater (p less than 0.05-p less than 0.001) than those of the WKY in Group I. A similar tendency was also observed for the content of adrenal epinephrine. The average concentrations of adrenal epinephrine and norepinephrine of SHR and SHRSP in Group II and III were significantly (p less than 0.05-p less than 0.001) greater than those of the respective rats in Group I, but no significant differences were noted in the blood pressure between pressure-treated groups (II, III) and the control group (I). Adrenalectomized SHR, SHRSP and WKY rats (Group V) had similar blood pressure levels as the control rats (Group I). The development of hypertension in SHR and SHRSP was effectively suppressed by the treatment with hydralazine, which, however failed to reduce concentrations of adrenal epinephrine and norepinephrine in these rats. These results indicate that increased adrenomedullary function in SHR and SHRSP is further enhanced by hyperbaric oxygenation treatment, but that high concentrations of adrenal catecholamines are not required for the pathogenesis of spontaneous hypertension of these animals at this age.