Effect of constant light on fetal and maternal prolactin rhythms in sheep.
A 24-h rhythm of plasma PRL is present in fetal sheep. This rhythm is synchronized to an environmental clue (zeitgeber). We determined whether the light-dark cycle (L:D) is a zeitgeber for the fetal PRL rhythm and, if so, whether the mother might convey this zeitgeber to the fetus. We kept nine ewes (twin pregnancies) in constant light (L:L) and five ewes (singleton) in 14:10 L:D from 110 days gestation. Fetuses and mothers were catheterized at 119 days gestation. Blood samples were taken hourly for 24 h after 16 days under L:L or L:D. A mean 24-h rhythm of PRL was found (by RIA) in fetuses under L:D, but not in those under L:L. However, fetuses under L:L showed individual 24-h PRL rhythms (cosinor analysis) whose acrophases were distributed around the clock. Nonsynchronized rhythms persisted after 23 and 30 days of L:L. Acrophases of PRL rhythms within a set of twins were closer than those between sets, suggesting that twins were responding to a common signal. These findings indicate that the L:D cycle is a zeitgeber for the PRL rhythm in fetal sheep and suggest that the mother might convey the zeitgeber.
Parraguez
V H
VH
Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile.
Valenzuela
G J
GJ
Vergara
M
M
Ducsay
C A
CA
Yellon
S M
SM
Serón-Ferré
M
M
D000818:Animals; D001683:Biological Clocks; D002940:Circadian Rhythm; D005260:Female; D005312:Fetal Blood / Q000378:metabolism*; D006321:Heart / Q000196:embryology / Q000502:physiology; D008027:Light; D008168:Lung / Q000196:embryology / Q000502:physiology; D017440:Photoperiod; D011247:Pregnancy; D011388:Prolactin / Q000097:blood*; D012756:Sheep
D011388:Prolactin