THE EFFECT OF VITAMIN-B-6 ON THE SYSTOLIC BLOOD-PRESSURE OF RATS IN VARIOUS ANIMAL-MODELS OF HYPERTENSION

Objective To investigate whether a dietary supplement of vitamin B-6 c ould attenuate the elevation of systolic blood pressure (SEP) in Zucke r obese or spontaneously hypertensive rats, or rats ingesting sucrose. Methods Zucker obese rats (fa/fa), Sprague-Dawley rats with sucrose-i nduced elevation of SEP, spontaneously hypertensive rats (SHRs) and th eir corresponding controls were tested for the effects of vitamin B in gestion in different ways: (1) vitamin B-6 was included as a supplemen t (five times the normal intake) from the start of the experiment unti l the development of hypertension; (2) vitamin B-6 supplement was remo ved from the diet of Zucker obese and Zucker lean control groups after 16 weeks on the dietary treatments; and (3) a diet deficient in vitam in Bs was instituted in SHRs and control Wistar-Kyoto (WKY) rats. The SEP of rats in all groups was monitored in the conscious animal by tai l-cuff plethysmography, The effects of the various treatments on the u ptake of calcium by caudal artery segments were examined. Results Male Zucker obese rats (fa/fa) of age 6 weeks fed a commercial rat chow de veloped hypertension in 3-4 weeks, whereas their lean controls (Fa/Fa) did not. The inclusion of a vitamin B-6 supplement (five times the no rmal intake) resulted in a complete attenuation of the hypertension in the obese strain. Removal of the vitamin B-6 supplement from the diet of these obese rats resulted in the return of hypertension within 2 w eeks. Similar changes in SEP were also observed in the Zucker lean con trols treated with vitamin B-6. The ingestion of sucrose by male Sprag ue-Dawley rats resulted in modest elevation of SEP that was attenuated by the inclusion of the vitamin B-6 supplement in their diet In contr ast, there was no response to the inclusion or removal of dietary vita min B-6 supplement in the SHRs. However, the WKY control rats responde d to both these conditions in a similar manner to that seen in the Spr ague-Dawley strain. Increased peripheral resistance resulting from inc reased permeability of vascular smooth muscle plasma membrane to Ca2is thought to be one of the mechanisms of hypertension. Changes in SBP correlated with changes in the uptake of calcium by caudal artery seg ments in all the groups studied, The Zucker obese and sucrose-induced hypertensive rats have abnormalities in carbohydrate metabolism. The v itamin B-6 supplement decreased the random or fasting blood glucose le vels in the Zucker obese and sucrose-fed rats respectively. Conclusion This is the first observation that animal models of hypertension can be classified on the basis of their response to a vitamin B-6 suppleme nt. On this basis, the etiology of hypertension in SHRs is quite disti nct from that in Zucker obese rats and in rats ingesting sucrose.