Browsing by Author "CARDENAS, H"
Now showing 1 - 9 of 9
Results Per Page
Sort Options
- ItemA STUDY ON THE FEASIBILITY OF SUPPRESSING OVARIAN ACTIVITY FOLLOWING THE END OF POSTPARTUM AMENORRHEA BY INCREASING THE FREQUENCY OF SUCKLING(1988) DIAZ, S; MIRANDA, P; BRANDEIS, A; CARDENAS, H; CROXATTO, HBThe aim of the study was to test the effect of increasing the frequency of breastfeeding upon ovarian function following the end of postpartum amenorrhoea. Women exclusively breastfeeding (n = 14) who experienced their first postpartum menstruation between the third and fifth month after delivery were randomly allocated to an experimental (n = 7) and a control (n = 7) group and studied during the next two cycles. Women in the experimental group agreed to increase the number of breastfeeding episodes per day throughout the second cycle. Blood samples were drawn twice a week from the first to the third postpartum menstruation for prolactin, oestradiol and progesterone determinations. The number of breastfeeding episodes per day and night and the length of each episode were recorded daily. An average frequency of 11 nursing episodes per 24 h was reported during the first study cycle in both groups. The experimental group increased by 50% of the breastfeeding frequency after the second menstruation while the control group kept its spontaneous feeding pattern. The increase of suckling frequency occurred mainly during day hours. The total breastfeeding time per 24 h was not increased. The length of the menstrual cycle was not altered by the increased suckling frequency. The endocrine pattern differed neither between the first and second cycle of the experimental group nor between the experimental and control group, with the exception of PRL levels which were higher in the experimental gorup throughout both cycles. Twenty cycles (71%) showed progesterone values compatible with ovulation (> 9.5 nmol/l). The highest progesterone values and the highest oestradiol values observed in the ovulatory cycles of lactating women were within the range found in non-nursing fertile women. Plasma levels of PRL were significantly elevated in all cycles but one, in comparison with PRL levels in non-nursing women. It is concluded that if cyclic ovarian function is reestablished early in fully nursing women, a mere increase in the number of breastfeeding episodes, without augmenting total suckling time and the frequency of nocturnal episodes, does not provide a sufficient stimulus to resuppress the pituitary-ovarian axis.
- ItemADDITIVE EFFECT OF RU-486 AND ANORDRIN ON PREGNANCY INTERRUPTION IN THE MOUSE(1993) FORCELLEDO, ML; CARDENAS, H; CROXATTO, HBThe effect of various doses of anordrin and RU 486, alone or combined, on serum progesterone (P) levels, fetal resorption, and recovery of ovulation was studied in mice. Each drug was given as a single sc injection on day 7 of pregnancy and autopsy was performed on days 8, 9, or 11. Serum P was normal at 24 h but fell significantly 48 h after treatment with anordrin (0.05 mg). Doses of 0.05 or 0.2 mg anordrin were effective in interrupting pregnancy in 30% and 70% of pregnant mice, respectively. RU 486, 0.01 mg per mouse, induced a pronounced decrease of P levels 24 h after treatment and interrupted pregnancy in 50% of pregnant mice. The combined treatment with submaximal doses of anordrin plus RU 486 did not further decrease P levels, but increased the proportion of mice with fetal resorptions to 90%. The combination of small doses of anordrin with RU 486 had an additive effect on pregnancy termination. The additive effect required a dose of RU 486 above the threshold level. Direct observation of aborted fetuses indicated that the resorptive process occurred earlier with RU 486 than with anordrin. Recovery of ovulation was associated with pregnancy termination in a high proportion of mice treated with either drug or their combination.
- ItemCIRCADIAN 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, HBThe 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.
- ItemDOPAMINE-INDUCED VENTILATORY DEPRESSION IN THE RAT, MEDIATED BY CAROTID NERVE AFFERENTS(1981) CARDENAS, H; ZAPATA, PIn pentobarbitone-anesthetized rats, i.v. injections of dopamine (DA) at 10-8-10-5 g/kg led to transient ventilatory depression, usually not associated with changes in systemic arterial pressure. DA-induced ventilatory depression consisted of decreases in tidal volume and respiratory frequency in 12 rats and in bradypnea without changes in tidal volume in 5 rats. After bilateral section of the carotid nerves, ventilatory responses to DA were abolished or greatly diminished. DA evidently inhibits carotid body chemosensory discharges in the rat. Chemosensory activity may directly affect respiratory frequency.
- ItemDUAL EFFECTS OF DOPAMINE UPON CHEMOSENSORY RESPONSES TO CYANIDE(1980) CARDENAS, H; ZAPATA, PChanges in chemosensory responses to i.v. NaCN during i.v. infusions of dopamine (DA) were studied in pentobarbitone-anesthetized cats. After sectioning both carotid nerves, 1 of them was prepared for electrophysiological recordings of its chemosensory impulses. Basal chemosensory activity was maintained at a reduced level during DA infusions at a rate of 10 .mu.g/kg per min. While sensitivity to NaCN was not modified, reactivity to this agent was reduced for low doses, but enhanced for high doses. Chemoreceptor responses to histotoxic hypoxia are evidently rectified by DA. This is discussed in terms of a modulatory role of endogenous DA in the generation of carotid body sensory impulses.
- ItemEFFECTS OF BODY-TEMPERATURE ON CHEMOSENSORY ACTIVITY OF THE CAT CAROTID-BODY INSITU(1991) LOYOLA, H; FADIC, R; CARDENAS, H; LARRAIN, C; ZAPATA, PThe effects of changes in body core temperature (T(B)) upon the frequency of chemosensory discharges (f(x)) from one carotid nerve were studied in pentobarbitone anesthetized cats. Raising T(B) from 35 to 40-degrees-C increased f(x) in some cats, an effect more commonly seen after contralateral carotid neurotomy. In other animals, the simultaneously increased alveolar ventilation counteracted the above effect. A multiple correlation analysis of global data showed predicted increases in f(x) in response to raising T(B) at different CO2 levels.
- ItemLUTEINIZING-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, HBThe 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.
- ItemRELATIVE CONTRIBUTIONS OF ANOVULATION AND LUTEAL PHASE DEFECT TO THE REDUCED PREGNANCY RATE OF BREAST-FEEDING WOMEN(1992) DIAZ, S; CARDENAS, H; BRANDEIS, A; MIRANDA, P; SALVATIERRA, AM; CROXATTO, HBObjective: To evaluate the contribution of anovulation and luteal phase defects to lactational infertility.
- ItemVENTILATORY REFLEXES ORIGINATED FROM CAROTID AND EXTRACAROTID CHEMORECEPTORS IN RATS(1983) CARDENAS, H; ZAPATA, PVentilatory responses to transient stimulation and inhibition of arterial chemoreceptors, by hypoxia and hyperoxia, respectively, were studied in 10 pentobarbitone-anesthetized rats. N2 tests and i.v. injections of NaCN provoked transient increases in tidal volume and respiratory frequency, while O2 tests elicited decreases of these parameters. After bilateral carotid neurotomy, ventilatory responses to N2 and NaCN were still present although reduced in all rats, while ventilatory depression in response to O2 tests was observed in 60% of these rats. Further bilateral sectioning of main vagus, aortic and superior laryngeal nerves immediately below the nodose ganglia abolished the ventilatory responses to NaCN in only 1 of the 5 rats subjected to this procedure, the remaining animals showing moderate hyperventilation in response to large doses of this drug. Mild ventilatory depression in response to hyperoxia, indicative of a persistent peripheral chemosensory drive, was still present in 2 of these rats. Apparently although the carotid bodies constitute the main source of ventilatory chemoreflexes in rats, other vagally and nonvagally innervated chemoreceptors (presumably thoracic and abdominal) may elicit ventilatory reflexes in this species.