EFFECT OF CHRONIC TREATMENT WITH PRAZOSIN AND L-ARGININE ON THE ELEVATION OF BLOOD-PRESSURE DURING COLD-EXPOSURE

Chronic exposure to cold (5 degrees C) is well known to increase both tyrosine hydroxylase (TH) activity in brown adipose tissue and systemi c blood pressure. The effect of chronic dietary administration of the a-adrenergic antagonist, prazosin, and the amino acid, L-arginine, on both the elevation of blood pressure during exposure to cold and on TH activity and expression of TH mRNA in the adrenal glands of rats was studied. As observed previously, chronic exposure to cold increased sy stolic blood pressure significantly and induced cardiac hypertrophy. C hronic dietary treatment with prazosin (8 mg/kg food) and arginine (20 g/kg food) returned blood pressure to control levels, did not affect body weight significantly, but failed to prevent cardiac hypertrophy. Both prazosin and L-arginine reduced the drinking response to administ ration of angiotensin II. Treatment with arginine and prazosin was acc ompanied by a significant increase in the urinary outputs of dopamine and L-DOPA, The 3 cold-treated groups (control, L-arginine and prazosi n) had increases in plasma T-3 and decreases in plasma T-4 and plasma renin activity. Plasma concentrations of epinephrine and norepinephrin e were increased significantly in the L-arginine-treated group. TH mRN A and TH activity in the adrenal glands were increased in the 3 cold-t reated groups and these measures were correlated directly and signific antly with plasma norepinephrine and epinephrine concentrations. Altho ugh both prazosin and arginine prevented the cold-induced elevation of blood pressure, they did not prevent the increase in TH mRNA, TH acti vity or epinephrine in plasma. The protective effect of arginine and p razosin in cold-induced hypertension may be related both to their redu ction in plasma renin activity and to a reduced responsiveness to angi otensin II, as well as to their abilities to increase the secretion of dopamine.