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Biomedical subjects

S E Recabarren

Publications and source records attributed to S E Recabarren.

At least 19 recordsLinked to original sources
PubMed2004

Patterns of hormonal response to the GnRH agonist leuprolide in brothers of women with polycystic ovary syndrome: a pilot study.

BACKGROUND: The aim of this study was to evaluate the effect of a single dose of leuprolide acetate on gonadotrophin and gonadal steroid secretion in brothers of women with polycystic ovary syndrome (PCOS), in order to assess P450c17alpha activity. An oral glucose tolerance test (OGTT) and a lipid profile were also performed. METHODS: Twenty-two unrelated brothers of women with PCOS (PCOS(b)) and 14 brothers of normal cycling women (C(b)), matched for age, underwent a leuprolide acetate test (10 microg/kg s.c.) and an OGTT with measurement of circulating concentrations of gonadotrophins, steroid hormones, glucose, insulin and lipids. RESULTS: Clinical and basal hormonal parameters were similar in both groups. After leuprolide administration, PCOS(b) exhibited a significant increase of 17alpha-hydroxyprogesterone (17-OHP) compared to C(b) (P<0.05). However, only 45% of PCOS(b) showed a supranormal increase of 17-OHP (2 SD above the respective control group mean values, P<0.003) with a normal gonadotrophin response (group 1). The other 55% of the PCOS(b) exhibited a normal 17-OHP response to the analogue (group 2). However, in group 2, basal steroid concentrations did not show a uniform pattern: six of the PCOS(b) exhibited high basal androstenedione (2 SD above the respective control group mean values), three were very similar to C(b), and the other three presented lower basal testosterone concentrations (2 SD below the respective control group mean values) than those observed in C(b). CONCLUSIONS: This study shows that different responses to leuprolide in PCOS brothers make evident the heterogeneity of this syndrome in which P450c17alpha activity could be involved.

17-alpha-Hydroxyprogesterone↗
PubMed2002

Maternal serum androgens in pregnant women with polycystic ovarian syndrome: possible implications in prenatal androgenization.

BACKGROUND: The aim of this study was to evaluate the peripheral serum androgen concentrations in normal and polycystic ovarian syndrome (PCOS) women during pregnancy, in order to establish if PCOS may induce gestational hyperandrogenism and therefore constitute a potential source of androgen excess for the fetus. METHODS: Twenty pregnant PCOS (PPCOS) women and 26 normal pregnant (NP) women of similar age with singleton pregnancies were selected for the study. During gestational weeks 10-16 and 22-28, a 2 h, 75 g oral glucose tolerance test (OGTT) was performed. For the OGTT, glucose and insulin were measured in each sample and testosterone, androstenedione, dehydroepiandrosterone sulphate (DHEAS), estradiol, progesterone and sex hormone-binding globulin were determined in the fasting sample. RESULTS: In the first study period (gestational weeks 10-16), the levels of androstenedione, testosterone and DHEAS and the free androgen index tended to be higher in the PCOS group. These differences became significant in the second study period (gestational weeks 22-28). In this second period, 2 h insulin concentrations were also significantly higher in PPCOS than in NP women. CONCLUSIONS: The present study demonstrates a significant increase in androgen concentrations during pregnancy in PCOS women. We propose that these androgen concentrations could provide a potential source of androgen excess for the fetus, without leading to fetal virilization.

Adolescent↗
PubMed2001

Secretory pattern of leptin and LH during lactational amenorrhoea in breastfeeding normal and polycystic ovarian syndrome women.

Several studies have suggested that leptin modulates hypothalamic-pituitary-gonadal axis function. A synchronicity of LH and leptin pulses has been described in healthy women and in patients with polycystic ovarian syndrome (PCOS), suggesting that leptin may modulate the episodic secretion of LH. The aim of the present investigation was to assess the episodic fluctuations of circulating LH and leptin during lactational amenorrhoea in fully breastfeeding normal and PCOS women at 4 and 8 weeks postpartum, in order to establish LH-leptin interactions in the reactivation of the gonadal axis during this period. Six lactating PCOS patients and six normal lactating women of similar age and body mass index were studied. During a 12 h period on the 4th and 8th weeks postpartum, blood samples were collected at 10 min intervals for 12 h (22:00-10:00). Serum LH and leptin concentrations were measured in all samples. For pulse analysis, the cluster algorithm was used. To detect an interaction between LH and leptin pulses, an analysis of co-pulsatility was employed. LH concentrations tended to increase in both groups between the 4th and 8th weeks postpartum; however, serum leptin concentrations were not modified. Leptin pulse frequencies were similar at the 4th and 8th weeks postpartum, and did not differ between groups. Moreover, leptin pulse frequency was higher than LH pulse frequency in both groups, and in the two study periods. There was no synchronicity between LH and leptin pulses, and there were no increments in leptin concentration during the night. The fact that leptin concentrations were not modified and no synchronicity between LH and leptin pulses was observed suggests that, during lactational amenorrhoea, circulating leptin is probably not involved as a primary signal in promoting the reactivation of pulsatile LH secretion.

Adult↗
PubMed2001

Resumption of ovarian function during lactational amenorrhoea in breastfeeding women with polycystic ovarian syndrome: metabolic aspects.

BACKGROUND: Polycystic ovarian syndrome (PCOS) is a common endocrine-metabolic disorder in women, a high percentage of whom exhibit peripheral insulin resistance. After delivery, in normal women, lactation imposes a metabolic adaptation, the impact of which on the insulin resistance of PCOS patients is not known. The aim of this study was to evaluate the effect of lactation on insulin resistance, glucose and insulin metabolism, and sex hormone-binding globulin (SHBG) and insulin-like growth factor binding protein-1 (IGFBP)-1 concentrations in fully breast-feeding normal and PCOS women during the postpartum period (lactational amenorrhoea) and also after weaning. METHODS: Twelve lactating PCOS (LPCOS) women and six normal lactating (NL) women of similar age and body mass index (BMI) were selected for the study. At the 4th and the 8th week postpartum (pp), and 8 weeks after weaning, a 2 h, 75 g oral glucose tolerance test (oGGT) was performed, followed by an insulin tolerance test 2 days later. For the oGGT, glucose and insulin were measured in each sample and SHBG and IGFBP-1 were determined in the fasting sample. RESULTS: During lactation, fasting insulin levels were similar in both groups. In LPCOS women 2 h insulin concentrations were significantly higher, and SHBG and IGFBP-1 concentrations were significantly lower, than those observed in NL women. In both groups, insulin sensitivity evaluated by the insulin tolerance test was not modified. After weaning, in LPCOS women, SHBG and IGFBP-1 concentrations remained lower and insulin concentrations remained higher than those observed in NL women ( P < 0.05 ). CONCLUSIONS: In PCOS women, insulin resistance is not modified during lactation. Lactation has a transitory beneficial effect on insulin levels and biological markers of insulin resistance.

Adult↗
PubMed2001

Resumption of ovarian function during lactational amenorrhoea in breastfeeding women with polycystic ovarian syndrome: endocrine aspects.

BACKGROUND: The aim of this study was to evaluate the changes in gonadotrophin concentrations and the dynamics of the episodic fluctuations of circulating LH during night-time, in fully breastfeeding normal women and in those with polycystic ovarian syndrome (PCOS) during lactational amenorrhoea and after weaning, in order to provide insights into the onset of this syndrome. Additionally, ovarian activity was evaluated by ultrasound examination and steroid concentrations. METHODS: Twelve lactating PCOS (LPCOS) women and six normal lactating (NL) women of similar age were selected. On the 4th and 8th week postpartum (PP) and eight weeks after weaning, blood samples were collected every 10 min (10.00--20.00h). Gonadotrophin concentrations were determined in all samples. Steroid hormones were measured in one fasting sample and ovarian morphology was assessed by ultrasound. RESULTS: On the 8th week PP, LH pulse frequency was higher and FSH concentrations were lower in LPCOS women compared with NL women, and steroid hormone concentrations remained low, except for androstenedione which was higher in LPCOS patients. After weaning, similar differences were observed between both groups. PCOS patients also showed enlarged ovaries with a PCOS pattern in the three study periods. CONCLUSIONS: The enlarged ovaries associated with higher androstenedione concentrations suggest that PCOS is a primary ovarian defect, making it difficult to establish if the abnormal LH pattern observed in these women is primary or secondary to the ovarian dysfunction.

Adult↗
PubMed2000

Pituitary responsiveness to diurnal and nocturnal GnRH pulses in melatonin-treated ewe lambs.

It has been shown that oral administration of melatonin to Suffolk ewe lambs, from 10 weeks of age onwards, advances the onset of puberty compared with control lambs maintained under the same natural photoperiod. Luteinizing hormone (LH) pulse frequency at 20 and 26 weeks of age was unchanged by melatonin. However, LH pulse amplitudes greater than 1 ng mL(-1) were consistently observed in melatonin-treated lambs, suggesting either a high responsiveness of the pituitary gland to endogenous gonadotrophin-releasing hormone (GnRH) pulses, or a large amount of GnRH released by each pulse. The purpose of the present study was to assess the pituitary responsiveness to six diurnal and six nocturnal exogenous pulses of GnRH (10 ng kg(-1) bodyweight) in melatonin-treated ewe lambs (3 mg melatonin daily at 1600 hours, from 10 weeks of age; n = 5) and control lambs of the same age (n = 5), born in the spring and kept under natural photoperiod. Pulses of GnRH were given intravenously at 60-min intervals by means of an indwelling jugular catheter from 0900 to 1400 hours and from 2100 to 0200 hours to ewe lambs of 20 and 26 weeks of age. Blood samples were collected at 10-min intervals using a contralateral jugular vein catheter from 1 h before and up to 1 h after the last GnRH pulse. The difference (delta) between plasma LH concentrations at 0 min and the greatest concentration of LH after each GnRH pulse was calculated and compared in the same group. The total area under the GnRH response curve (AUC) was also calculated and compared within and between the groups. The AUC of melatonin-treated lambs (66.1 +/- 5.94 and 52.24 +/- 7.42 ng mL(-1)/6 h, diurnal and nocturnal respectively) was greater than that of control lambs (39.42 +/- 4.29 and 32.82 +/- 3.6 ng mL(-1)/6 h diurnal and nocturnal respectively; P<0.05) at 20 weeks of age. At 26 weeks of age, only the diurnal total AUC was greater in melatonin-treated lambs than in control lambs (60.17 +/- 7.98 and 29.8 +/- 5.02 ng mL(-1)/6 h respectively; P<0.05). Delta LH concentrations in response to the first diurnal pulse of GnRH were greater than those in response to the fifth diurnal GnRH pulse (P<0.05) in melatonin-treated lambs of 20 weeks of age. Also, the delta LH concentrations in response to the first three diurnal GnRH pulses were greater than to the last three nocturnal pulses of GnRH (P<0.05). Delta LH concentrations were greater in response to the second diurnal pulse of GnRH than to the last three diurnal GnRH pulses, and greater than the responses to the first and the last four nocturnal GnRH pulses (P<0.05), at 26 weeks of age in melatonin-treated lambs. The response to nocturnal pulses of GnRH was similar. In control lambs, the responses to diurnal and nocturnal GnRH pulses were similar at 20 and 26 weeks of age. These results suggest that melatonin enhances the pituitary responsiveness to GnRH pulses in ewe lambs.

Aging↗
PubMed1999

Episodic leptin release is independent of luteinizing hormone secretion.

Several studies suggest that leptin modulates hypothalamic-pituitary-gonadal axis functions. Leptin may stimulate release of gonadotrophin releasing hormone (GnRH) from the hypothalamus and of gonadotrophins from the pituitary. A synchronicity of luteinizing hormone (LH) and leptin pulses has been described in healthy women and in patients with polycystic ovarian syndrome, suggesting that leptin may modulate the episodic secretion of LH. However, it has not been established whether LH regulates the episodic secretion of leptin. To further examine LH-leptin interactions, we studied the episodic fluctuations of circulating LH and leptin in two patients with Kallmann's syndrome (KS) before and on day 7 of pulsatile GnRH administration, and compared these with those observed in the early follicular phase of 10 regularly menstruating women divided into two control groups according to the body mass index of each patient. To assess episodic hormone secretion, blood samples were collected at 10 min intervals for 6 h, before and on day 7 of GnRH administration in KS patients, and during days 3-7 of the follicular phase in normally cycling women. LH and leptin concentrations were measured in all samples. For pulse analysis, the cluster algorithm was used. Before treatment, an apulsatile pattern with no endogenous LH pulsations was observed in both KS patients. However, leptin pulses were assessed in both women. During GnRH administration, pulsatile LH activity was achieved in both patients with pulse characteristics similar to those of the respective control group. Serum leptin concentrations and leptin pulsatile patterns were not modified. These results suggest that circulating leptin is probably not modulated by pulsatile GnRH-LH secretion.

Adult↗
PubMed1999

Are circulating leptin and luteinizing hormone synchronized in patients with polycystic ovary syndrome?

Animal and human studies suggest that leptin modulates hypothalamic-pituitary-gonadal axis functions. Leptin may stimulate gonadotrophin-releasing hormone (GnRH) release from the hypothalamus and luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion from the pituitary. A synchronicity of LH and leptin pulses has been described in healthy women, suggesting that leptin probably also regulates the episodic secretion of LH. In some pathological conditions, such as polycystic ovarian syndrome (PCOS), LH-leptin interactions are not known. The aim of the present investigation was to assess the episodic fluctuations of circulating LH and leptin in PCOS patients compared to regularly menstruating women. Six PCOS patients and six normal cycling (NC) women of similar age and body mass index (BMI) were studied. To assess episodic hormone secretion, blood samples were collected at 10-min intervals for 6 h. LH and leptin concentrations were measured in all samples. For pulse analysis the cluster algorithm was used. To detect an interaction between LH and leptin pulses, an analysis of copulsatility was employed. LH concentrations were significantly higher in the PCOS group in comparison to NC women, however serum leptin concentrations and leptin pulse characteristics for PCOS patients did not differ from NC women. A strong synchronicity between LH and leptin pulses was observed in NC women; 11 coincident leptin pulses were counted with a phase shift of 0 min (P = 0.027), 18 pulses with a phase shift of -1 (P = 0.025) and 24 pulses with a phase shift of -2 (P = 0.028). PCOS patients also exhibited a synchronicity between LH and leptin pulses but weaker (only 20 of 39 pulses) and with a phase shift greater than in normal women, leptin pulses preceding LH pulses by 20 min (P = 0.0163). These results demonstrate that circulating leptin and LH are synchronized in normal women and patients with PCOS. The real significance of the apparent copulsatility between LH and leptin must be elucidated, as well as the mechanisms that account for the ultradian leptin release.

Adult↗
PubMed1996

Luteinizing hormone pulse frequency is increased by arginine infusion in prepubertal sheep.

Puberty in sheep is initiated by a complex neuroendocrine interplay which cascades into an increased LH pulsatility at this time. Blood-borne amino acids have been proposed as metabolic signals for the stimulation of GnRH/LH secretion, a mandatory requirement for pubertal onset. In previous experiments we have demonstrated that a 1 h infusion of L-arginine (ARG) was capable of stimulating the LH secretion in prepubertal ewes. The aim of the present study was to further examine the effect of an intravenous infusion of ARG on LH secretion. Prepubertal ewes were infused for 6 h with 15 (Group ARG15, n = 5) or 30 g (Group ARG30, n = 5) of L-ARG dissolved in 500 mL saline (pH 7.4), while saline was administered as control (Group S, n = 5). Since ARG is metabolized to ornithine (ORN), equimolar doses of L-ORN were additionally tested (Group ORN12 and ORN24, n = 5, respectively). Blood samples were obtained at 15 minute intervals during and after experimental infusions to characterize the LH pulsatile secretion. The resulting hormone data arrays were searched for significant fluctuations by the PULSAR program. The LH pulse frequency was found to be higher in groups of ARG treated than in saline or ORN infused sheep during the 6-h infusion period: 5.6 +/- 1.0 (ARG15) vs. 5.0 +/- 0.5 (ARG30) vs. 2.0 +/- 0.9 (S, p < 0.01) vs. 3.4 +/- 0.9 (ORN12) vs. 3.4 +/- 0.9 pulses/6 h (ORN24, p < 0.05). The total number of pulses was higher in ARG infused lambs than in saline or ORN infused animals: 11.2 +/- 1.2 (ARG15) vs. 10 +/- 1.1 (ARG30) vs. 13.8 +/- 1.4 (S) vs. 5.8 +/- 1.7 (ORN12) vs. 5.8 +/- 2.0 pulses/12h (ORN24), respectively. The LH mean secretion was comparable during both 6-h periods in all groups. Results of our experiments demonstrate increased LH pulse frequencies during ARG infusions, suggesting an action of ARG to stimulate hypothalamic GnRH release. Thus, ARG may be a critical determinant for enhanced LH pulsatility as a prerequirement for the onset of puberty in the sheep.

Analysis of Variance↗
PubMed1996

Effect of arginine and ornithine infusions on luteinizing hormone secretion in prepubertal ewes.

Although activation of the hypothalamic GnRH pulse generator is known to initiate the onset of puberty in immature animals, the metabolic cues by which information about the stage of body growth and development are translated into central nervous activity remain obscure. In the present study, the function of L-arginine (ARG) or L-ornithine (ORN) as promoters of pulsatile LH secretion was investigated in 2-mo-old prepubertal ewes. Suffolk ewe lambs (n = 17) fitted with intrajugular catheters were divided into three groups. Saline (200 mL) was infused for 1 h into all lambs. In Group 1, saline infusion was continued for another hour. In Group 2, 200 mL of an ARG solution (350 mM, pH 7.4) was infused for 1 h, and in Group 3, ORN was infused (200 mL, 350 mM, pH 7.4) for 1 h. Blood samples were collected at 15-min intervals from 60 min before until 285 min after the end of infusions. The Pulsar program was used to identify significant LH episodes during 285 min after infusions. Mean LH concentrations during the 285-min period after infusion were greater (P < .05) in Group 2 than in Groups 1 and 3. The mean LH pulse frequencies and amplitudes did not differ among the groups. However, in lambs infused with ARG, 13 of their 17 LH pulses had amplitudes > 1 ng/mL, whereas in control ewes only 5 of 20 pulses had amplitudes > 1 ng/mL. All of the ARG-infused ewes had two or more LH pulses with amplitudes > 1 ng/mL; only 1 of 6 control lambs had two pulses. Results indicate that ARG stimulates LH secretion in prepubertal ewes.

Aging↗
PubMed1995

A simple device for serial blood collection in human subjects and animals.

A simple system for the continuos withdrawal of blood and the serial collection of blood samples in human subjects and experimental animals is described. It consists of heparin-coated tubing, a connector attached to an indwelling cannula that allows flushing of the i.v. catheter, a peristaltic pump and a fraction collector and an alarm system which is activated when blood flow through the system is interrupted. It can be assembled from parts available in every laboratory or hospital.

Animals↗
PubMed1992

Biochemical and physiological parameters and estimated work output in draught horses pulling loads for long periods.

A study was undertaken in five draught horses of 648 +/- 33 kg body weight to find the effects of continuously pulling loads on their cardiovascular, respiratory and metabolic responses. A cart equipped with an odometer, for measuring distance, and a hydraulic dynamometer, for measuring draught force, was used. Heart and respiration rates and rectal temperatures were recorded. Blood samples for measuring arterial and venous pH and blood gases, haemoglobin, glucose and lactic acid concentrations and the serum activity of the enzymes creatine phosphokinase (CK), lactate dehydrogenase, aspartate aminotransferase and alkaline phosphatase were taken before exercise and immediately after each journey (morning and afternoon) of the daily work. Draught exercise, with loads which generated forces of between 0.57 and 0.59 kN, at speeds of 1.60 to 2.11 m/s, for 8 h daily for five consecutive days, with resting intervals of 10 min each hour, was well tolerated. Exercise tolerance was evaluated from the recovery from the changes observed in the biochemical and physiological parameters induced by the work. The analysis of these showed that, when the horses were subjected to prolonged periods of resting, their loss of fitness for work was shown by significant increases in the serum activity of muscle-derived enzymes and in blood lactate concentrations during the first day of work. However, over the following days the horses adapted to the work, so that the decreases in serum enzyme activities and blood lactate concentrations were reduced. Since similar observations have been described for racehorses, the determination of blood lactate concentrations and the serum activities of muscle-derived enzymes, specifically CK, seem to be good indicators of fitness in draught horses.

Acid-Base Equilibrium↗
PubMed1992

Cardiorespiratory parameters in draught horses before and after short term draught work pulling loads.

In order to establish the relationship between draught force and cardiorespiratory responses to exercise heart rate (HR), respiratory rate (RR), arterial and venous blood gases, pH, hemoglobin concentration and temperature were measured in five draught horses during rest, immediately after exercise and 30 min post-exercise under field conditions. A wagon equipped with an odometer and a hydraulic dynamometer was used for measuring distance and draught force. The wagon was loaded with 946 kg for the low load, 1,979 kg for the medium load and 2,994 kg for the high load, and drawn for a distance of 1,500 m. Draught force and load weight were linearly related. The response of the draught horse to low and medium load exercise was characterized by a moderate increase in HR, RR and temperature with no significant changes in arterial blood gases and pH. An increase in HR, RR and temperature was observed, whereas no changes in arterial PO2 and increases in venous PO2 were noticed after high load exercise. Slight increase in venous lactic acid concentration as a result of high load exercise was observed, suggesting that some anaerobic work was performed. However this was insufficient to produce changes in blood pH. The increase in metabolic requirements during the three levels of draught exercise was associated with increases in arterial hemoglobin concentration and oxygen content of blood.

Acid-Base Equilibrium↗
PubMed1991

Plasma luteinizing hormone bioactivity and immunoactivity in ovariectomized rats treated with a long-acting agonist of luteinizing hormone releasing hormone.

The dose response of a luteinizing hormone releasing hormone (LHRH) agonist in rats with high endogenous gonadotrophin levels was determined. Female rats were ovariectomized and injected with 0.3 microgram (group B), 3.2 micrograms (group C), 32 micrograms (group D) and 320 micrograms (group E) of a slow-releasing microcapsule preparation of the LHRH agonist D-Trp 6-LHRH. Control ovariectomized rats (group A) remained untreated. Plasma luteinizing hormone (LH) concentrations were measured by radioimmunoassay (RIA) before the LHRH agonist injection as well as 5, 15 and 30 days thereafter. Furthermore, LH bioactivity was determined by an in vitro rat LH bioassay in order to evaluate changes in bioactivity after administration of LHRH agonist. In control rats, plasma LH concentrations increased to 4.8 +/- 1.3 ng/ml on day 5, reaching peak levels of 9.9 +/- 1 ng/ml on day 30. In contrast to the control group, those rats which received 320 micrograms of LHRH agonist did not show any increase. Rats which received intermediate doses (groups C and D) tended to maintain levels of LH halfway between group A and group E during the first 15 days of treatment. Thereafter LH concentrations were similar to the untreated control group. The course of the LH concentrations during treatment measured by bioassay (BA) showed a similar pattern to the LH concentrations measured by RIA. The BA/RIA ratio was similar in all groups.

Animals↗
PubMed1990

Disappearance of opioidergic tone on LH secretion in underfed prepubertal sheep.

A study was conducted to determine whether an opioid tonus inhibitory of LH secretion is present in underfed prepubertal sheep. Ten Suffolk ewe lambs were subjected to food restriction during 60 days. During this period they were allowed to pasture only 2 hours per day while control ewe lambs were allowed for 10 hours. Body weight and plasma blood levels of glucose, urea and total proteins were measured weekly. At the end of this period, an intravenous injection of Naloxone (NAL, 1.5 mg/kg BW) was given to control and underfed animals followed 60 min later by an intravenous injection of LHRH to test the pituitary responsiveness. Underfed animals did not show an increase in plasma LH while control animals presented a rise from 0.28 +/- 0.08 to 2.02 +/- 0.6 ng/ml after the NAL stimulus (P less than 0.05). The response to LHRH was similar in both group of animals. Basal plasma levels of insulin were lower in underfed ewe lambs than in control animals (P less than 0.05). Underfed animals were placed on plain feeding with a schedule similar to control lambs for 30 days and the same experiment was repeated. During this occasion, NAL increased plasma LH concentration in both group of lambs. Levels of plasma insulin were not different in both groups. The lack of effect of NAL on LH secretion in food restricted ewe lambs suggests that the opioid modulation of LH secretion is absent by underfeeding in female prepubertal sheep.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Effect of naloxone and luteinizing hormone releasing hormone pulses on plasma luteinizing hormone concentration in ewe lambs.

A study was conducted to determine the effect of pulses of naloxone on plasma LH concentration in prepubertal ewes and to see if this treatment affects the pituitary response to subsequent LHRH pulses. Prepubertal ewes (n = 5) received three intracarotidal pulses of naloxone (NAL, 1 mg/kg BW) and four pulses of Luteinizing Hormone Releasing Hormone (LHRH, 1 micrograms/pulse) at hourly intervals. Control ewes (n = 5) received saline instead of NAL followed by the LHRH pulses at the same frequency. Blood samples were collected from one hour before the first pulse of saline or NAL at 15 min intervals for four hours and at 30 min intervals for another four hours. Plasma LH concentration was measured by radioimmunoassay. The first pulse of NAL increased plasma LH levels compared to the basal levels and compared to control animals (P less than 0.01). The succeeding pulses were ineffective. LHRH provoked an increase in plasma LH concentration in control as well as in treated animals but the amplitude of the net peak height increased progressively up to the third pulse in NAL treated animals, while there was no increase in pituitary responsiveness to LHRH in control prepubertal ewes. Also, the area under the LHRH response curve was greater (P less than 0.05) in animals pretreated with NAL than in lambs pretreated with saline. The results suggest that there is an inhibitory opioid tone over LH secretion in female lambs. NAL increases the responsiveness to exogenous LHRH pulses, probably as a result of endogenous LHRH release.

Animals↗
PubMed1987

Circadian variation of rectal temperature in newborn sheep.

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 degrees 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 less than 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 less than 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.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗