Ontogeny of baroreflex control of renal sympathetic nerve activity and heart rate
Segar, J.L.; Hajduczok, G.; Smith, B.A.; Merrill, D.C.; Robillard, J.E.
American Journal of Physiology 263(6 Pt 2): H1819-H1826
1992
ISSN/ISBN: 0002-9513 PMID: 1481906 Document Number: 404979
The purpose of this study was to characterize the developmental changes in baroreflex function during fetal and postnatal life in sheep. Resting mean arterial blood pressure increased significantly from 55 +- 2 mmHg in fetuses to 86 +- 3 mmHg in newborn lambs and to 105 +- 4 mmHg in 4- to 6-wk-old lambs. The sensitivity (gain) of the renal sympathetic nerve activity (RSNA) response to baroreceptor stimulation was greater (P lt 0.05) in fetuses (-7.7 +- 1.9%/mmHg) than in newborn (-2.9 +- 0.1%/mmHg) and 4- to 6-wk-old lambs (-2.2 +- 0.2%/mmHg). The threshold and saturation pressures for the baroreflex function curve were lower (P lt 0.05) in fetuses (44 +- 2 and 61 +- 2 mmHg) than in newborn (59 +- 4 and 106 +- 5 mmHg) or 4- to 6-wk-old lambs (78 +- 5 and 132 +- 6 mmHg). Similar findings were observed when the heart rate response to baroreceptor stimulation was examined. Additional experiments were performed in newborn and 4- to 6-wk-old lambs to determine whether the rise in arterial blood pressure associated with postnatal maturation contributed to baroreflex resetting. Sustained elevation of arterial blood pressure by 15-20 mmHg for over 90 min did not reset the baroreflex function curve in either newborn or 4- to 6-wk-old lambs. These results indicate that 1) baroreceptor stimulation controls sympathetic outflow as well as heart rate during fetal life, 2) functional baroreflex control of RSNA and heart rate shifts toward higher pressure during development, 3) the sensitivity (gain) of the baroreflex function curve for RSNA is greater in fetuses than in newborn or 4- to 6-wk-old lambs, and 4) elevation of arterial blood pressure in newborn and 4- to 6-wk-old lambs is not associated with resetting of the baroreflex.