The physiologic baroreceptor activity and fetal plasma amino acids under chronic hypoxemia in fetal lamb.

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(Objective)The purpose of this study was to investigate the variation of baroreflex (BR) and fetal plasma concentrations of amino acids under the chronic hypoxemia in the fetal lamb.(Methods)We conducted BR experiments and measurement of fetal plasma concentrations of amino acids simultaneously on nine chronically instrumented fetal lambs (100〜127 days of gestation). Continuous infusion of nitrogen into maternal trachea induced the fetal hypoxic condition. To analysis fetal BR activity, injections of 5 - 7.5 μg of norepinephrine were given during consecutive behavioral cycle on the 1, 5, 10, 15th day in normoxemic or hypoxemic groups. In fetal lambs, mean arterial blood pressure (MAP) and FHR was measured dividing into active states (AS) and sleep states (SS) which were determined retrospectively by reactivity or fetal breathing movements. The ratio of maximal FHR decrease to maximal MAP increase (ΔFHR/ΔMAP) response to the norepinephrine injections was calculated to quantitatively rep … More resent fetal BR activity. Furthermore, we classified behavior state into sleep state (SS) and active state (AS), and classified into the hypoxemia group (H group) and the normoxemia group (N group). Thereafter, we did single regression analysis about the relation between the gestational age (GA) and ΔFHR/ΔMAP.(Results and Conclusions)The increasing in GA induced decreasing of BR in both states and in both groups.N group : Y=-0.042X+8.306(p=0.043)(AS) Y=-0.046X+8.57(p=0.0007)(SS)H group : Y=-0.041X+7.63(p=0.017)(AS), Y=-0.063X+10.0(p=0.021)(SS)These date suggested that under chronic hypoxemia the decreasing of BR with increasing in GA was more significant than that of the controls in fetal lamb.Fetal plasma concentrations of the branched chain amino acids, that were needed to produce protein and energy in fetuses, showed a decrease tendency in chronic hypoxemia in comparison with other amino acids conspicuously. Fetal plasma concentrations of the glycogenetic amino acids, that were significantly decreased under maternal starvation, did not show a decrease tendency in chronic hypoxemia. Less