Baroreceptor sensitivity in two-week-old rat pups: effects of nutrient deprivation and sino-aortic denervation

Resting cardiac rates are reduced 40% by nutrient deprivation in two-week-old rats while arterial pressure is maintained at stable levels. Previous evidence implicated arterial baroreceptors and suggested the hypothesis that the cardiac rate changes result from increased baroreceptor sensitivity following nutrient deprivation. In order to test this hypothesis, cardiac reflex responses were elicited by graded doses of phenylephrine and sodium nitroprusside before and after nutrient deprivation. Although cardiac rate decelerations in response to phenylephrine were greater in fed pups (p less than 0.05) and acceleration in response to nitroprusside were greater in the deprived condition (p less than 0.01), these could be attributed to 'ceiling' and 'floor' effects of the resting cardiac rates characteristic of the two nutrient conditions. Sino-aortic denervation eliminated cardiac reflex responses, substantiating their dependence on baroreceptor afferents. Regression analysis of cardiac reflex responses to arterial pressure changes failed to show changes in baroreceptor sensitivity that would support the hypothesis. Alternate mechanisms mediating the nutrient effect on cardiac rate (e.g., involving neural and peptide hormonal pathways) should be pursued.