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Changes in ovine renal sympathetic nerve activity and baroreflex function at birth
J L Segar1, J E Mazursky, J E Robillard
1Department of Pediatrics, University of Iowa, Iowa City 52242.
The American Journal of Physiology
|November 1, 1994
Summary
Newborn sheep exhibit increased renal sympathetic nerve activity (RSNA) and altered baroreflex function post-birth. Angiotensin II does not drive these changes, but its inhibition resets baroreflexes to lower pressures.
Area of Science:
- Physiology
- Neonatal Physiology
- Cardiovascular Regulation
Background:
- Renal sympathetic nerve activity (RSNA) and baroreflex function undergo significant changes at birth.
- Understanding these perinatal cardiovascular adjustments is crucial for neonatal health.
Purpose of the Study:
- To characterize changes in RSNA and baroreflex function in conscious sheep immediately after birth.
- To investigate the role of elevated circulating angiotensin II (ANG II) in these newborn adaptations.
Main Methods:
- Measurements of RSNA and baroreflex curves (renal and heart rate) in fetal and newborn sheep.
- Administration of an angiotensin-converting-enzyme inhibitor (enalaprilat) to assess ANG II's role.
Main Results:
- RSNA significantly increased after birth compared to fetal levels.
- Baroreflex curves for RSNA and heart rate showed resetting towards higher pressures.
- Inhibition of ANG II did not affect the postnatal rise in RSNA but reduced baroreflex midpoint pressures.
Conclusions:
- Postnatal increases in RSNA and baroreflex resetting occur independently of high circulating ANG II levels.
- ANG II inhibition influences baroreflex pressure thresholds in newborn lambs.