Effects of low-protein diet on the baroreflex and Bezold-Jarisch reflex in conscious rats

The present study evaluated the effects of a low-protein diet (LP, 6% protein) on cardiovascular reflexes of Male Fisher rats. Three experimental groups, and their respective controls (15% protein), were used: (1) Baroreceptor reflex (BAR); (2) Bezold-Jarisch reflex (BJR); and (3) Prazosin treated. Dietary restriction began after weaning (three weeks) and lasted for a period of five weeks, after which animals were subjected to the experimental protocols. The BAR group was evaluated through injections of phenylephrine (0.5-5.0 microgram/Kg, i.v.) and sodium nitroprusside (0.7-7.0 microgram/Kg, i.v.) while the BJR was evaluated through injections of serotonin (2.5-10 microgram/Kg, i.v.). Our results showed an increased baroreflex gain bradycardia for the LP group (-0.96+/-0.34 vs. -2.12+/-1.06 bpm/mmHg) and a larger bradycardia for the BJR the LP group (160+/-18% greater than controls). Basal cardiovascular parameters were not different between LP and control rats, however LP animals treated with prazosin resulted in a larger fall of blood pressure (-19+/-3 vs. -28+/-5 mmHg). In conclusion, LP rats present an increased responsiveness of BAR and BJR, which could contribute to their normal levels of cardiovascular parameters, in spite of the possible increase in the sympathetic vasomotor tonus observed with the prazosin protocol.