Influence of vitamin B-6 on the renin--angiotensin system in rats

The effects of treatment with pyridoxine or 4-desoxypyridoxine, a vitamin B-6 antimetabolite, and of vitamin B-6 deprivation on the blood pressure response to renin and angiotensin II and on plasma angiotensin concentration and renin activity were studied in Long-Evans hooded rats in order to compare the effects on these factors of vitamin B-6 excess or vitamin B-6 deficiency. Both pyridoxine and 4-desoxypyridoxine caused a progressively increasing inhibition of the response to renin, which was totally suppressed after 24 days of treatment. They had no significant effect, however, on the basal blood pressure, the response to angiotensin II, plasma angiotensin levels, or plasma renin activity. The vitamin B-6-free diet caused an increase in basal blood pressure of 23 +/- 5 mmHg, over a period of 5 weeks, along with a simultaneous decrease in the response to renin and, though to a lesser degree, angiotensin II. The basal blood pressure remained steady at this level and then decreased again, after the 10th week of deprivation, while the response to renin remained low. Plasma angiotensin levels increased from 0.40 +/- 0.06 ng/ml in control animals to 0.97 +/- 0.06 ng/ml in the deficient rats, and plasma renin activity increased from 5.19 +/- 0.35 to 11.31 +/- 1.56 ng of angiotensin I/ml/hour.