Physiologic baroreceptor activity in the fetal lamb.
OBJECTIVE
We investigated the influences of gestational age and behavioral state on fetal baroreceptor activity.


METHODS
Two protocols were used to analyze low-voltage fast activity and high-voltage slow activity in eight chronically instrumented ovine fetuses at days 127 to 142. In protocol 1 correction of fetal heart rate to mean arterial blood pressure was assessed under physiologic conditions, and the linear regression slope of fetal heart rate on mean arterial pressure was calculated. In protocol 2 an injection of 7.5 micrograms of norepinephrine was given during consecutive behavioral cycles. The ratio of fetal heart rate decrease to mean arterial pressure increase was determined as representing baroreceptor activity.


RESULTS
Under protocol 1 the slope was steeper in high-voltage slow activity (2.33 +/- 1.03) than in low-voltage fast activity (0.89 +/- 0.37) (n = 21, p less than 0.001), indicating that fetal heart rate changes are sensitive to blood pressure changes during high-voltage slow activity. Under protocol 2 inverse relationships were found between the ratio of fetal heart rate decrease to mean arterial pressure increase and gestational age in low-voltage fast activity and high-voltage slow activity.


CONCLUSIONS
Fetal baroreceptor activity increased during high-voltage slow activity and decreased with gestational age.
Wakatsuki
A
A
Department of Obstetrics and Gynecology, University of California, Irvine, College of Medicine, UCI Medical Center, Orange 92613-1491.
Murata
Y
Y
Ninomiya
Y
Y
Masaoka
N
N
Tyner
J G
JG
Kutty
K K
KK
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D001794:Blood Pressure; D005318:Fetal Heart; D005333:Fetus / Q000502:physiology*; D005865:Gestational Age; D006339:Heart Rate; D011311:Pressoreceptors / Q000502:physiology*; D012018:Reflex / Q000502:physiology; D012044:Regression Analysis; D012756:Sheep / Q000196:embryology; D013618:Tachyphylaxis