Ming Li, Tafline Fraser, Jian Wang* and Judith A Whitworth

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Abstract
1. The effects of L-arginine treatment on dexamethasone-induced hypertension were examined in the Sprague-Dawley rat. Seventy rats were randomly divided into the following eight groups: sham, dexamethasone (5 and 10 micrograms/day, L-arginine (100 and 500 mg/kg per day), L-arginine (100 or 500 mg/kg per day) + dexamethasone (10 micrograms/day), L-arginine (520-797 mg/kg per day in food) + dexamethasone (5 micrograms/day). Systolic blood pressure (SBP), bodyweight and plasma nitrate/nitrite concentration were measured. 2. Dexamethasone (5 and 10 micrograms/day) increased SBP in both sham and L-arginine-treated rats. Dexamethasone at 10 micrograms/day decreased bodyweight, but did not alter plasma nitrate/nitrite concentrations. 3. L-Arginine (500 mg/kg per day, i.p.) increased plasma nitrate/nitrite concentrations in 10 micrograms/day dexamethasone-treated rats. L-Arginine did not alter blood pressure in either sham or dexamethasone-treated rats. 4. Dexamethasone-induced hypertension differs from adrenocorticotropic hormone (ACTH)-induced hypertension in the rat in that it is not modified by L-arginine. Thus, ACTH-induced hypertension cannot be explained simply in terms of glucocorticoid activity.