Increased arterial pressure variability after arterial baroreceptor denervation in fetal lambs

Baroreceptor reflexes can be demonstrated during fetal life, but whether baroreceptors normally regulate fetal arterial pressure is unknown. This problem was addressed directly by measuring arterial pressure and analyzing its variation in eight unanesthetized fetal lambs throughout the last third of gestation, and comparing these data with similar measurements made in seven fetal lambs with denervated arterial baroreceptors. Measurements were made at 5-minute intervals over 24 hours in a total of thirty-three experiments. The coefficient of variation of mean arterial pressure (standard deviation of mean arterial pressure/mean value of mean arterial pressure) expressed as a percentage was used as an index of blood pressure variability. Coefficients averaged 7.0% in intact lambs and 12.1% in barodenervated lambs (P less than 0.001), signifying considerably increased variability of mean arterial pressure after barodenervation. Mean arterial pressure averaged over 24 hours was not different between the two groups prior to 120 days (0.8) of gestation. Between 120 days and term, mean pressure was significantly greater in the denervated fetuses (65 cm H2O) than in the sham-operated controls (60 cm H2O, P less than 0.025). These data demonstrate that a baroreceptor-blood pressure reflex functions during late gestational development in lambs and signify an important role of arterial baroreceptors in regulating fetal arterial pressure. Failure to regulate arterial pressure in the barodenervated fetus could result in significant alterations in placental perfusion and exchange, and in the regional delivery of oxygen and substrates to developing organs in these animals.