Browsing by Author "Parraguez, VH"

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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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    Post-coital administration of levonorgestrel does not interfere with post-fertilization events in the new-world monkey Cebus apella
    (2004) Ortiz, ME; Ortiz, RE; Fuentes, MA; Parraguez, VH; Croxatto, HB
    BACKGROUND: Experimental evidence to disprove the belief that emergency contraception with levonorgestrel (LNG) prevents pregnancy by interfering with post-fertilization events is lacking. Here we determined the effect of post-coital and pre-ovulatory administration of LNG on fertility and ovulation, respectively, in the Cebus monkey. METHODS: To determine the effect on fertility, LNG 0.75 mg or vehicle were administered orally or s.c. once or twice within the first 24 h after mating occurring very close to the time of ovulation. Females that became pregnant were aborted with mifepristone and re-entered the study after a resting cycle until each of 12 females had contributed, in a randomized order, two LNG and two vehicle-treated cycles. To determine the effect on ovulation, LNG 0.75 mg or vehicle were injected twice coinciding with follicles smaller or larger than 5 mm in diameter. Six females contributed five treated cycles each. RESULTS: The pregnancy rate was identical in vehicle- and LNG-treated cycles. LNG inhibited or delayed ovulation only when treatment coincided with a follicle <5 mm diameter. CONCLUSION: In Cebus monkeys, LNG can inhibit or delay ovulation but, once fertilization has taken place, it cannot prevent the establishment of pregnancy. These findings do not support the hypothesis that emergency contraception with LNG prevents pregnancy by interfering with post-fertilization events.
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    Study of prenatal growth in the capuchin monkey (Cebus apella) by ultrasound
    (1998) Corradini, P; Recabarren, M; Serón-Ferré, M; Parraguez, VH
    Capuchin monkey (Cebus apella) is a new world primate that in recent years has become important in biomedical research. The purpose of this study was to establish and correlate normal fetal growth parameters with gestational age in capuchin monkeys. In seven pregnant animals serial ultrasonic assessment of gestational sac (GS), embryo/fetal greatest length (GL), biparietal diameter (BPD), thorax height (TH), and femur length (FL) were performed. Identification of the GS was possible on day 23 +/- 2.8 (X +/- SE). The embryo and its heartbeat was detected on day 32.7 +/- 2.8, the GL being measurable thereafter. By day 45.4 +/- 1.4 BPD and TH were measurable. FL could only be measured from day 70.6 +/- 2.1. Predictive regression equations of gestational age (GA) were modeled with data obtained. In addition, preliminary data of fetal heart rate showed a decrease in frequency with advancing gestation.