Browsing by Author "Vergara, M"

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    Effect of constant light on fetal and maternal prolactin rhythms in sheep
    (1996) Parraguez, VH; Valenzuela, GJ; Vergara, M; Ducsay, CA; Yellon, SM; SeronFerre, M
    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.
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    Impact of lactation upon fertility in the New World primate capuchin monkey (Cebus apella)
    (2000) Recabarren, MP; Vergara, M; Martínez, MC; Gordon, K; Serón-Ferré, M
    In the present paper, we have studied the impact of lactation upon fertility in the capuchin monkey, Cebus apella, under laboratory conditions. Nursing females (ten females, 12 postpartum periods) presented lactational amenorrhea (first menses at 159.2 +/- 9.0 vs 42.6 +/- 5.8 days postpartum in five non-nursing females, seven postpartum periods). Plasma estradiol and progesterone concentrations during lactational amenorrhea were lower than those during the follicular phase of the menstrual cycle. Prolactin was higher than in non-nursing females at 31-60 days postpartum. Interbirth interval, studied in three nonnursing (four intervals) and six nursing females (eight intervals) lasted for 349.5 +/- 11.8 and 613.4 +/- 30.8 days, respectively. In non-nursing females, early recovery of the menstrual cycle was followed by a residual infertility (mating but no pregnancy) lasting 152.8 +/- 7.9 days. In nursing females, recovery of the menstrual cycle was followed by an extended residual infertility of 301.5 +/- 22.7 days. Thus, in the capuchin monkey, nursing prolongs the interbirth interval by inducing lactational amenorrhea and extending the residual infertility period.