Browsing by Author "SERONFERRE, M"

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    CIRCADIAN VARIATION OF BASAL PLASMA PROLACTIN, PROLACTIN RESPONSE TO SUCKLING, AND LENGTH OF AMENORRHEA IN NURSING WOMEN
    (1989) DIAZ, S; SERONFERRE, M; CARDENAS, H; SCHIAPPACASSE, V; BRANDEIS, A; CROXATTO, HB
    The circadian pattern of plasma PRL levels and the PRL response to suckling were examined at various times during the first postpartum year and related to the length of lactational amenorrhea. Ten healthy women whose infants were breast-fed exclusively and who were amenorrheic 3 months postpartum were studied 3, 6, and 9-11 months postpartum. The women and their babies were admitted to a metabolic unit for 48 h. On the second day, blood samples were drawn at 2-h intervals for 26 h starting at 0800 h and also 10 and 30 min after the initiation of six of the nursing episodes. During the three postpartum periods, there was a circadian rhythm of basal plasma PRL concentrations; the peak concentrations occurred between 2400-0600 h. Suckling induced a significant rise in plasma PRL levels at all hours except 0800 h. There was a positive correlation between the duration of the nursing episode and the suckling-induced PRL increase at 30 min. Both the basal plasma PRL levels and the PRL responses to suckling diminished with time after delivery. This trend was less evident at 0400 h and was not fully explained by changes in the nursing pattern. The five women in whom menstrual cycles resumed before day 180 postpartum had lower basal and suckling-induced plasma PRL levels than in the women who had amenorrhea for a longer period. This difference was present in the third month, when all women were amenorrheic and fully nursing and when the frequency and duration of nursing episodes and infant growth rates were similar. The results indicate that comparable nursing patterns may be associated with different plasma PRL levels, which are associated with different lengths of lactational amenorrhea. An early difference in the sensitivity of the breast-hypothalamus-pituitary system to suckling may explain the differences in the duration of lactational amenorrhea, which are not dependent on the breastfeeding pattern. The magnitude of the PRL response to suckling may predict the likelihood of recovering ovarian function during lactation.
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    CIRCADIAN VARIATION OF RECTAL TEMPERATURE IN NEWBORN SHEEP
    (1987) RECABARREN, SE; VERGARA, M; LLANOS, AJ; SERONFERRE, M
    In adult animals, body temperature shows a 24 h rhythm that is endogenously generated. We examined the existence of 24 h rhythms of temperature in 10 newborn sheep. Four newborns, aged 5 to 28 days were kept with their mothers under nycthemeral conditions, and the remaining 6 lambs, aged 21 to 43 days, were kept with their mothers in constant light from day 3 after birth. Experiments were performed with both groups of lambs in the laboratory. Additional experiments were performed with the 6 lambs kept under constant light while they were in the pen with their mothers to rule out artifacts due to manipulation or artificial feeding. During the experiments done in the laboratory, the lambs were kept blindfolded in a canvas sling and were fed baby formula approximately every four hours (lambs kept under nycthemeral conditions) or every hour (constant light lambs). Lights were on in the room during the whole experiment. Temperature in the room was maintained at 18 .+-. 0.1.degree. C (mean .+-. SEM). In the experiments done in the pen, animals remained with the mother and room temperature was not controlled. In all experiments, rectal temperature was hourly measured for 24 h with a thermocouple inserted in the lamb''s rectum and connected to a Philipp Schenk digital recorder. Lambs kept under nycthemeral conditions show a variation of mean rectal temperature (t.degree.) with a period of 24 h, that fits a cosine function (P < 0.001): Rectal t.degree. (.degree.C)=40.6 + 0.4 cos [15 (t-16.22)]. The mesor is 40.6, the amplitude 0.4, and the acrophase expressed in h is 16.22 (n=4). Lambs kept under constant light show a variation of rectal temperature with a period of 24 h, independently of whether the measurements were done in the laboratory or in the pens. The acrophases varied widely in these animals, when the acrophase were synchronized so .theta.=2400, mean rectal temperature showed a variation with a period of 24 h that fits the equation (P < 0.001): Rectal t.degree. (.degree.C)=39.5 + 0.18 cos [15 (t-0.23)]. The presence of a 24 h rhythm of rectal t.degree. in lambs kept under nycthemeral conditions, and its persistence in lambs kept under constant light suggests that the rhythm of rectal temperature observed in the newborn lamb is a true circadian rhythm. From these data it can be inferred therefore, that the part of the circadian system controlling core body temperature is functional in the newborn lamb.
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    LUTEINIZING-HORMONE PULSATILE RELEASE AND THE LENGTH OF LACTATIONAL AMENORRHEA
    (1995) DIAZ, S; CARDENAS, H; ZEPEDA, A; BRANDEIS, A; SCHIAPPACASSE, V; MIRANDA, P; SERONFERRE, M; CROXATTO, HB
    The pattern of luteinizing hormone (LH) pulsatile release and the mean concentrations of follicle-stimulating hormone, oestradiol and progesterone were studied in nursing and non-nursing women. Blood samples were drawn at 5 min intervals between 10:00 and 14:00 h and between 22:00 and 02:00 h at months 3-4, 5-6, 7-8 and 9-10 post-partum in nursing women and in the follicular phase in non-nursing women. In nursing women, mean LH concentrations at months 3-4 were significantly lower than in non-nursing cycling women only in the subgroup which subsequently experienced >6 months of lactational amenorrhoea, although all were fully nursing with a similar suckling frequency. LH pulses in plasma were found at all times in nursing women. There were no significant differences in the frequency (about four pulses every 4 h), amplitude or duration of LH pulses related to the duration of amenorrhoea, nor did these parameters vary significantly between amenorrhoeic or cycling nursing women and nonnursing women. Nursing amenorrhoeic women exhibited a normal frequency of LH pulse well in advance of the resumption of the first post-partum menses, suggesting that mechanisms other than the suppression of the gonadotrophin-releasing hormone pulse generator intervened in the inhibition of ovarian function during lactation.
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    ONTOGENY OF THE CIRCADIAN-RHYTHM OF CORTISOL IN SHEEP
    (1989) PARRAGUEZ, VH; VERGARA, M; RIQUELME, R; RAIMANN, R; LLANOS, AJ; SERONFERRE, M
    In this work we investigated the ontogeny of the rhythm of plasma cortisol in sheep. Plasma cortisol was measured by radioimmunoassay in blood samples obtained every 1 or 2 h, for periods of 24 or 48 h, in 13 fetal sheep (124-140 days of gestation; 130.6 .+-. 1.5, mean .+-. SE) and in 23 newborn (5-39 days of age). To this end, indwelling polyvinyl catheters were implanted into the femoral artery and vein in all animals. The presence of rhythm was determined by Cosinor Analysis. Newborns were separated into four groups. Group 1, newborns younger than 15 days of age (7.9 .+-. 0.7 days), and Group 2, newborns older than 15 days of age (25.4 .+-. 2.3), were raised under nyctohemeral conditions (12L:12D). Group 3, newborns younger than 15 days of age (11.4 .+-. 0.9 days), and Group 4, newborns older than 15 days of age (22.0 .+-. 1.2 days), were raised under constant light conditions. A 24-h rhythm of plasma cortisol (F) was observed in newborns over 15 days of age under both nyctohemeral: F (ng/ml) = 16.1 .+-. 7.6 cos [15 (t-12.9)], (p = 0.01, n = 8) and constant llight conditions: F (ng/mL) = 17.1 + 3.9 cos [15 (t-7.9)], (p = 0.02, n = 5). No rhythm was observed in fetal sheep or in newborn sheep younger than 15 days of age under nyctohemeral or constant light conditions.