Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Estrus”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17Linked to original sources
PubMed1988

The effects of buck teasing on synchronization of estrus in goats after intravulvo-submucosal administration of cloprostenol.

A study was conducted on 35 East African shorthorned female goats to determine if a combination of buck teasing and low doses of a prostaglandin (PGF(2) alpha) analogue, cloprostenol, given intravulvo-submucosally (i.v.s.m.) would be suitable for synchronization of estrus. Goats were allotted, with the onset of estrus, to seven groups (n = 5 goats per group). Five of the seven groups received varying doses of cloprostenol: Group 1 (125 microg cloprostenol i.m. per goat); Group 2 (62.5 microg cloprostenol i.v.s.m. per goat); Group 3 (62.5 microg cloprostenol i.v.s.m. per goat plus buck teasing); Group 4 (31.25 microg cloprostenol i.v.s.m. per goat); Group 5 (31.25 microg cloprostenol i.v.s.m. per goat plus buck teasing); Group 6 (buck teasing); Group 7, (2 ml physiological saline i.v.s.m. per goat, control group). Plasma progesterone concentration was measured on day of treatment and for 6 d thereafter. All goats in groups 1, 2, 3 and 5 exhibited estrus within 68 h. Thus, the number of goats receiving low doses of PG-cloprostenol intravulvo-submucosally observed in estrus increased (P < 0.05) with exposure to bucks. Exhibition of behavioral signs of estrus was maximal between 2 and 20 h after onset of signs of estrus. The exposure of females to males prior to intrauterine penetration was an advantage because copious mucus eased penetration.

Journal Article↗
PubMed1996

Induction and synchronization of estrus in goats: the relative efficiency of one versus two fluorogestone acetate-impregnated vaginal sponges.

The purpose of the experiment was to test the hypothesis that a variable and/or insufficient level of progestagen at the end of a treatment to synchronize estrus in goats could explain variability in the onset of estrus. The experiment was performed during the anestrous season on 2 herds, one of Alpine (n = 49) the other of Saanen (n = 53) dairy goats. The animals were allocated to 1 of 3 treatments: Group 1 received a vaginal sponge impregnated with 45 mg of fluorogestone acetate (FGA) on Day 0; Group 2 received a sponge on Day 0 plus a second sponge on Day 7; Group 3 received a sponge on Day 0 plus a second sponge on Day 9. The sponges were withdrawn on Day 11. All goats received 400 or 500 IU eCG and 50 mug PGF(2alpha) analog 48 h prior to sponge removal. They were inseminated with frozen-thawed semen 24 h after the onset of estrus. Among treatment groups no difference (P > 0.05) was observed for the following parameters: percentage of goats in estrus, percentage of goats ovulating, mean time and variability of onset of estrus. The fertility of Alpine goats in Group 3 was significantly decreased (P < 0.05). No effect on prolificacy was noticed. These observations show that to increase progestagen level at the end of treatment did not improve estrus synchronization. They provide further evidence that treatments with too high progestagen amounts can decrease fertility.

Journal Article↗
PubMed2000

Estrus synchronization in ewes treated with sponges impregnated with different doses of medroxyprogesterone acetate.

The objectives of this study were to determine residual and absorbed levels of medroxyprogesterone acetate (MAP) after treatment with intravaginal sponges impregnated with different doses of MAP in an ewe herd and to determine the effects of such treatments upon estrus incidence, interval to estrus onset and pregnancy rate. Polyurethane sponges impregnated with 40, 50 and 60mg of MAP were prepared. Real amounts of progestagen on sponges were checked prior to sponge treatment insertion. During autumn 1999, 608 cyclic Merino ewes were treated with intravaginal sponges impregnated with different doses of MAP (groups I, 40; II, 50 and III, 60mg). After 14 days, sponges were removed and residual levels of MAP (RMAP) on removed sponges were measured by spectrophotometry. Real amounts for unused sponges were 39.60+/-1.10, 44.10+/-1.06 and 59.10+/-1.26mg for the intended doses of 40, 50 and 60mg MAP respectively. RMAPs were different (p<0.05) among groups (I: 17.98+/-1.97mg; II: 24.32+/-2.03mg; III: 34.25+/-3.23mg). Absorbed levels of MAP were not different among groups (I: 21.62+/-1.97mg; II: 19.78+/-2.03mg; III: 24.85+/-3.23mg). Artificial insemination was performed in 16 ewes from Group I, 17 ewes from Group II and 11 ewes from Group III, 12h after estrus onset. There were no differences among groups, neither for estrus incidence (I: 79.27%; II: 77.42%; III: 80.87%) nor interval to estrus onset (I: 55.94+/-1.87h; II: 56.74+/-1.13h; III: 57.70+/-1.02h). There were also no differences among groups for pregnancy rate (I: 43.75%; II: 52.94%; III: 45.45%). It was concluded that under similar conditions, a dose as low as 40mg MAP could be effectively used for estrus synchronization in cyclic Merino ewes.

Journal Article↗
PubMed2004

Sex and estrus cycle differences in the modulatory effects of morphine on seizure susceptibility in mice.

PURPOSE: To evaluate the effects of sex and estrus cycle on biphasic anticonvulsant and proconvulsant modulation of seizure threshold by morphine. METHODS: The threshold for the clonic seizures (CST) induced by acute intravenous administration of gamma-aminobutyric acid (GABA)-antagonist pentylenetetrazole (PTZ) was assessed in male and female mice. Estrus cycle was assessed by vaginal smears. The effect of removing circulating sex hormones was assessed by gonadectomy. RESULTS: At baseline, diestrus females had a higher CST compared with males and estrus females. Morphine at lower doses (0.5-3 mg/kg) had a significant anticonvulsant effect in males and estrus females compared with that in vehicle-treated controls, whereas female mice in diestrus phase showed a relative subsensitivity to this effect. Morphine at higher doses (30 and 60 mg/kg) significantly decreased CST in males and diestrus females, with less relative effect in estrus mice. In both phases, morphine exerted stronger effects in males compared with females. Ovariectomy brought the baseline CST to the male level and resulted in significant expression of both phases of morphine effect but did not abolish the sex difference in responsiveness to morphine. CONCLUSIONS: The biphasic modulation of seizure threshold is subject to both constitutive sex differences in sensitivity to morphine and hormonal fluctuations during the estrus cycle.

Animals↗
PubMed2006

Ovarian follicular and corpus luteum changes, progesterone concentrations, estrus and ovulation following estradiol benzoate/progesterone based treatment protocol in cross-bred cows.

The objectives of the present study were to investigate the effects of the stage of the estrous cycle at the start of an estradiol benzoate (EB) and progesterone (P) based treatment protocol on new follicular wave emergence, subsequent estrus and ovulation. The experiment was conducted using a crossover design with each cow (five cross-bred cows) being assigned to one of three groups at 3-month intervals within a 1-year period. Estrous cycle stage in individual cows was initially synchronized with prostaglandin F(2)alpha. After detection of estrus, each cow was injected intramuscularly (i.m.) with 2 mg EB and 200 mg P (EB/P) on day 5, 12 or 17 of the estrous cycle (estrus=day 0), followed by 1 mg EB i.m. 12 days after the EB/P treatment. Ovarian ultrasonographic examinations showed that the emergence of a new follicular wave occurred after EB/P treatment in all groups and the mean interval from EB/P treatment to wave emergence did not differ among the groups (3.2-3.8 days). All cows in each group exhibited behavioral estrus and ovulated the newly formed dominant follicle. However, cows in the day-17 group exhibited estrus 1-3 days before the second EB injection. The concentrations of progesterone showed faster reduction, during the treatment period, in the day-12 and -17 groups compared to the day-5 group. These results indicate that the EB/P treatment induces an emergence of a new follicular wave, irrespective of the estrous cycle stage at the start of treatment, but the effect of EB/P protocol on estrous/ovulation synchronization is influenced by the stage of the estrous cycle.

Animals↗
PubMed2004

Effect of the interval between estrus onset and artificial insemination on sex ratio and fertility in cattle: a field study.

We have carried out a field trial in cattle to study the effect of the interval between the onset of estrus and AI on sex ratio and fertility. Data were obtained from 716 cows that had been inseminated at different times between 8 and 44 h from the visual detection of estrus. Before analyzing the data, it was grouped in three intervals considering the time between estrus onset and AI (8-18, 18-30, and > or = 30 h). Our results show that the percentage of calved females (73.05%) is significantly superior for early inseminations (8-18 h), and it decreases 1.85% per hour from the onset of estrus. Delayed AIs (> or = 30 h) produce a significant deviation of the sex ratio towards the males (72.06%); nevertheless, fertility (percentage of successful pregnancies) diminishes significantly, from 66.19% (8-18 h) to 45.35% (> or = 30 h). In conclusion, variations in the interval between the onset of estrus and AI modify sex ratio. However, we must consider its effect on fertility.

Animals↗
PubMed2001

Estrus and pregnancy after synchrony with lutalyse in conjunction with Syncro-Mate-B.

Estrous response and pregnancy rates are decreased for cows given Syncro-Mate-B (SMB) during metestrus (Day 1 to 5 of an estrous cycle). Data indicate these decreases are due, in part, to retention of a functional corpus luteum (CL). Our objective was to determine whether PGF2alpha administered in conjunction with SMB would improve estrous response and pregnancy rates in metestrous cows with no detrimental effects to cows in other stages of the estrous cycle. Three hundred seventy-three suckled beef cows were observed for estrus for 21 d before SMB administration to determine stage of an estrous cycle. Blood samples were collected 14 and 7 d before treatment and at SMB administration. Serum was assayed for concentration of progesterone to verify stage of estrous cycle or noncyclicity. All cows received the standard SMB regime and were allotted by age and stage of cycle to one of two groups. Cows denoted SMB + L received 25 mg of PGF2alpha 8 d after implantation, whereas cows denoted SMB served as controls. On Day 10, SMB implants were removed and females were observed for subsequent estrus. At this time, calves were removed from their dams for 48 h. Artificial insemination was performed 12 hr after observation of a standing estrus. Timed insemination was performed at 48 hr after implant removal for cows not inseminated at 24 or 36 hr after implant removal. Interval to synchronized estrus (within 5 d of implant removal) was lengthened for metestrous cows compared to cows in other stages of the cycle irrespective of treatment (P < 0.001). Cows receiving PGF2alpha had a greater pregnancy rate at 5 d compared to controls (P = .0672). Interval to estrus, estrous response, and pregnancy rate to A1 at d 28 or end of breeding season were not affected by administration of PGF2alpha in conjunction with SMB when compared to the standard SMB protocol.

Animal Husbandry↗
PubMed2003

Endocrine events during the periestrous period and the subsequent estrous cycle in ewes after estrus synchronization.

The aim of the present study was to investigate the endocrinology of the periestrus period and that of the subsequent estrous cycle in ewes synchronized during the breeding season. Animals were treated for 14 days with either MAP intravaginal sponges or subcutaneous progesterone implants, followed by administration of 500 IU PMSG at the time of withdrawal. The time to estrus occurrence following progestagen withdrawal differed significantly between groups (45.3+/-2.7h for the MAP and 21.5+/-1.2h for the implant group, P<0.001). Estradiol levels around estrus did not differ between groups, but a significant difference was detected for the interval from peak estradiol to estrus, with a shorter interval for the implant group (26.7+/-0.7 and 2.7+/-0.9h, P<0.001). Progesterone implants shortened the interval from removal to LH surge, compared to the MAP group (31.2+/-4.4 and 56.5+/-3.6h, respectively, P<0.05). An earlier response was also observed for the interval from estradiol peak to LH peak in the implant group (12.1+/-3.3 and 37+/-2h, respectively, P<0.005), but no difference was observed for the interval from estrus to LH surge. Progesterone levels, particularly during the Days 6 to 10 of the subsequent estrous cycle were significantly higher (P<0.05) in the implant group. It is concluded that the kind of progesterone treatment may affect the time of estrus and the LH peak as well as the progesterone levels of the subsequent cycle.

Administration, Intravaginal↗
PubMed1990

Synchronization of estrus with melengestrol acetate and prostaglandin F2 alpha in beef and dairy heifers.

Beef (n = 783) and dairy (n = 209) heifers at 14 locations were used to evaluate the efficacy of feeding melengestrol acetate (MGA; .5 mg/d) for 7 d followed by an i.m. injection of 25 mg prostaglandin F2 alpha (PGF) on the last day of MGA feeding (MGA + PGF) to synchronize estrus. Untreated heifers (C) and heifers injected once i.m. with PGF served as contemporary controls. Heifers were observed for estrual behavior for a minimum of 38 d starting on the 2nd d of MGA feeding. Heifers in estrus from d 1 through d 60 after PGF injection were artificially inseminated (AI) or bred to bulls (d 30 to 60 post PGF only). During the 7-d MGA feeding period fewer (P less than .01) MGA + PGF (1.5%) than C (20.6%) or PGF (18.1%) heifers were observed in estrus. Percent of heifers in estrus d 1 to 6 post PGF was different among groups (P less than .05; 30.5, 52.8, 72.3 for C, PGF and MGA + PGF, respectively). More (P less than .01) MGA-fed (92%) than non-MGA-fed (C and PGF combined) heifers (85.4%) were observed in estrus during d 1 to 24. Conception rate (CR) during d 1 to d 6 was not different (P = .19) between C (58.9%) and MGA + PGF (51.2%) heifers; CR was lower (P = .01) for MGA + PGF than for PGF (68.3%) heifers.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1995

Synchronization of ovarian follicular waves with a gonadotropin-releasing hormone agonist to increase the precision of estrus in cattle: a review.

Treatment with GnRH and PGF2 alpha is a practical method for controlling ovarian follicular and luteal functions and increasing the precision of estrus synchronization in cyclic and acyclic postpartum cows and heifers. This method reduces considerably the period of time needed for estrus detection; it synchronizes the estrous cycle of 70 to 80% of the cyclic cows to within a 4-d interval without any detrimental effect on the fertility rate (65 to 85%). Moreover, resumption of ovarian activity and normal fertility in acyclic cows in favored. Administration of GnRH eliminates the large follicles by ovulation or atresia and induces emergence of a new follicular wave within 3 to 4 d after treatment at any stage of the estrous cycle, but it limits further growth of these emerging follicles by increasing atresia. The precision of estrus and the unaltered fertility rate is due to the synchronized selection of a new larger growing follicle, which becomes the ovulatory follicle after PGF(2 alpha)-induced luteolysis 6 d after GnRH treatment. Also, fixed-time AI programs without the need for estrus detection may be possible using a second injection of GnRH in a GnRH-PGF(2 alpha)-GnRH protocol to ovulate the selected follicle at a precise time. We describe a physiological model to explain how the precision of estrus is improved following PGF(2 alpha)-induced luteolysis, via the effect of pretreatment with GnRH on follicular development and luteal functions in cattle. Application of this model to the development of reliable methods of fixed-time insemination is also explored.

Animals↗
PubMed1998

Induced and synchronized estrus in cattle: dose titration of estradiol benzoate in peripubertal heifers and postpartum cows after treatment with an intravaginal progesterone-releasing insert and prostaglandin F2alpha.

Peripubertal beef heifers (n = 57) and postpartum multiparous cows (n = 52) were used to determine the optimal dose of estradiol benzoate (EB) to induce and synchronize estrus after treatment with intravaginal progesterone inserts (IVP4, EAZI-BREED CIDR). All females received an IVP4 for 7 d (d 0 = insertion day) with a 25-mg injection of PGF2alpha (Lutalyse) on d 6. At 24 to 30 h after IVP4 removal, females were randomly assigned to be injected subcutaneously with EB at the following doses: heifers 0, .2, .38, or .75 mg and cows 0, .25, .5, or 1 mg. Furthermore, seven heifers and seven cows from each dose group were bled every 4 h for 76 h starting at EB injection. Serum was collected and assayed for LH and estradiol-17beta (E2). Observations for signs of estrus were made twice daily for 21 d after removal of IVP4, and females were artificially inseminated 8 to 20 h after detection of estrus. The percentage of females showing estrous behavior was increased by EB (P < .04); the greatest response was at .38 mg in heifers (86%) and 1 mg in cows (100%). Dose x time interaction affected (P < .01) E2 concentrations in heifers and cows; the animals that received the higher doses of EB had greater E2 concentrations in a shorter time than those that received the smaller doses. The percentage of cows and heifers with an acute preovulatory LH release (peak LH) was affected by dose, with a linear (P < .01) and a quadratic (P < .01) response. Highest concentrations of LH during peak LH were affected by dose with a linear (P < .01) response in heifers and linear (P < .01) and quadratic (P < .08) responses in cows. Heifers receiving .38 mg and cows receiving .5 and 1 mg of EB had the highest peak LH. Time to LH peak had a linear (P < .03) response in heifers and had linear (P < .04) and quadratic (P < .05) responses in cows. Pregnancy rate was affected (P < .02) in heifers by whether or not they were anestrous before IVP4 treatment (those with estrous cycles = 52% vs those that were anestrous = 22%) and in cows by dose of EB (P < .01; 8, 23, 21, and 67% for 0, .25, .5, and 1 mg, respectively). In conclusion, in females treated with IVP4 and PGF2alpha to induce and synchronize estrus, an injection of EB increased concentrations of E2 and LH and increased number of animals showing estrus. Also, EB increased pregnancy rates in cows. Optimal responses were at .38 mg EB for heifers and at 1 mg EB for cows.

Administration, Intravaginal↗
PubMed2004

Synchronization of estrus in postpartum beef cows and virgin heifers using combinations of melengestrol acetate, GnRH, and PGF2alpha.

The efficacy of various combinations of melengestrol acetate (MGA), GnRH, and PGF2alpha for the synchronization of estrus in Angus-based beef cattle was compared. Hormones were administered as follows: MGA, 0.5 mg x animal(-1) x d(-1) mixed in a grain carrier; GnRH, 100 microg i.m.; PGF2alpha, 25 mg i.m. In Exp. 1, 2, and 3, cows were randomly assigned to treatments by parity and interval postpartum. The detection of estrus and AI were conducted from d -2 until 72 to 96 h after PGF2alpha, at which time cows not detected to be in estrus received GnRH and fixed-time AI (TAI). Data were analyzed separately for primiparous and multiparous cows. In Exp. 1, cows (n = 799) at three locations received GnRH on d -7 and PGF2alpha on d 0 and either no further treatment (GnRH-PGF) or short-term MGA from d -6 through d -1 (STMGA). Among multiparous cows, conception rate at TAI was greater (P < 0.05) for STMGA (41%, 47/115) than for GnRH-PGF treated cows (26%, 24/92). Across herds and parity, synchronized AI pregnancy rate (SPR) was not affected (P > 0.10) by treatment (GnRH-PGF vs. STMGA; 54%, 210/389 vs. 57%, 228/402). In Exp. 2, cows (n = 484) at three locations received either STMGA or long-term MGA from d -32 through d -19, GnRH on d -7, and PGF2alpha on d 0 (LTMGA). Among primiparous cows, SPR was greater (P < 0.01) in LTMGA (65%, 55/85) than STMGA-treated cows (46%, 40/87). Treatment had no effect (P > 0.10) on SPR among multiparous cows (STMGA vs. LTMGA; 59%, 92/155 vs. 64%, 101/157). In Exp. 3, cows (n = 838) at four locations received the LTMGA treatment and either no further treatment or an additional period of MGA exposure from d -6 through d -1 (L&STMGA). Among primiparous cows, SPR tended to be influenced (P < 0.10) by the herd x treatment interaction and was greater (P < 0.01) among L&STMGA (86%, 19/22) than LTMGA-treated cows (56%, 14/25) at a single location. Among multiparous cows, SPR was lower (P < 0.05) in L&STMGA (46%, 165/358) than LTMGA-treated cows (55%, 184/336). In Exp. 4, Angus heifers (n = 155) received either STMGA or 14 d of MGA (d -32 through d -19) and PGF2alpha on d 0 (MGA-PGF). The detection of estrus and AI were conducted from d -2 to d 6. Interval to estrus was greater (P < 0.05) and estrous response was lower (P < 0.05) in STMGA than MGA-PGF-treated heifers. In conclusion, primiparous cows responded more favorably to longer-duration MGA treatments than did multiparous cows. All protocols achieved sufficient SPR to justify their use for improved reproductive management of postpartum beef cows.

Animals↗
PubMed1997

Evaluation of different protocols for prostaglandin synchronization to improve reproductive performance in dairy herds with low estrus detection efficiency.

The objective of this study was to evaluate different PGF2 alpha protocols against control protocols for herds with estrus detection efficiencies of 35, 55, and 75% using modeling and simulation: 1) PGF2 alpha treatments based on the presence of a corpus luteum diagnosed by rectal palpation, 2) PGF2 alpha treatments based on the presence of a corpus luteum diagnosed by an on-farm milk progesterone enzyme immunoassay, and 3) PGF2 alpha treatments based on a 14-d fixed treatment schedule without prior screening for ovarian status. After the start of each protocol, estrus detection efficiency was 75% for 7 d after treatment and 35 or 0% for the following week. For the third protocol, an additional modification at estrus detection efficiencies of 85 and 55%, respectively, in the 1st and 2nd wk after treatment was evaluated to establish a protocol for best case assumptions. All protocols improved reproductive performance relative to that of controls with estrus detection efficiencies of 35 and 55%. The mean number of days open was reduced from 124.3 d in the control herd to 95.9, 95.0, and 92.7 for the protocols based on rectal palpation, milk progesterone test, and the fixed treatment schedule, respectively. The protocols based on a fixed treatment schedule were superior to protocols based on rectal palpation and on-farm milk progesterone tests and resulted in better reproductive performance and a higher increase in net return per cow per year. Relative to a control herd with an estrus detection efficiency of 55%, it was cost effective to spend up to $10 per dose of PGF2 alpha, $9 per milk progesterone test, and $6 per rectal palpation.

Animals↗
PubMed1998

Comparison of two estrus synchronization programs in a large, confinement-housed dairy herd.

OBJECTIVE: To compare pregnancy rates, seasonal effects, and economic benefits of 2 estrus synchronization programs for a confinement-housed dairy herd. DESIGN: Prospective cohort study. ANIMALS: 200 lactating Holstein cows. PROCEDURE: Cows eligible for breeding were palpated per rectum and randomly assigned to 2 treatment groups during 4 seasonal periods. Cows in one group (Ovsynch) received injections of gonadotropin releasing hormone (GnRH) on day 0, prostaglandin F2 alpha on day 7, and a second injection of GnRH on day 8. Cows in the other group (PP) that had a palpable corpus luteum were given prostaglandin F2 alpha. Estrus detection was not performed on the Ovsynch cows, which were artificially inseminated at a predetermined time after the second GnRH injection. Cows in the PP group were observed for signs of estrus, and only those that were detected in estrus were inseminated. RESULTS: Pregnancy rates and insemination rates were significantly improved for cows in the Ovsynch group, compared with cows in the PP group. CLINICAL IMPLICATIONS: The Ovsynch program was an economically advantageous method for controlling reproduction that resulted in pregnancies without the need for estrus detection.

Animal Husbandry↗
PubMed1991

In vitro and in vivo association of an oviduct estrus-associated protein with bovine zona pellucida.

The interaction between the bovine egg zona pellucida and a 97 kDa estrus-associated protein produced by the oviduct was examined in vitro and in vivo. In vitro matured bovine eggs were incubated with oviduct fluid recovered throughout the estrous cycle from separate indwelling cannulae placed in the ampulla and isthmus of the same oviduct. Immunofluorescence techniques and a polyclonal antiserum against the 97 kDa protein were used to localize this protein on washed eggs previously incubated with oviduct fluid. Intensity and distribution of immunofluorescence varied with stage of cycle and to a lesser degree with region of oviduct from which the oviduct fluid was obtained. The most intense fluorescence was observed on the zonae pellucidae of eggs incubated with oviduct fluid pooled from days near estrus and ovulation compared to fluid pooled from luteal stage days. The immunofluorescence of isthmus-derived oviduct fluid was more intense than was ampulla-derived oviduct fluid collected near estrus. The zonae pellucidae of 7-day-old embryos flushed from the uterus displayed immunofluorescence comparable to that observed on the zonae pellucidae of eggs incubated in vitro with peri-estrus oviduct fluid. No immunofluorescence was observed associated with the perivitelline space, egg cytoplasm, or blastomeres. The apparent uptake of a 97 kDa estrus-associated protein by the zonae pellucidae of eggs in vitro and embryos in vivo may indicate that this protein functions in fertilization and/or early embryo development.

Animals↗
PubMed1989

Effects of estrus cycle on thermoregulatory responses during exercise in rats.

In female rats, rectal temperature (Tre), tail vasomotor response, oxygen uptake (VO2), and carbon dioxide production (VCO2) were measured in proestrus and estrus stages during treadmill running at two different speeds at an ambient temperature (Ta) of 24 degrees C. Experiments were performed at 2.00-6.00 a.m., when the difference in Tre was greatest between the two stages; Tre at rest in the estrus stage was 0.54 degrees C higher than in the proestrus stage. In a mild warm environment, threshold Tre for a rise in tail skin temperature (Ttail) was also higher in the estrus stage than in the proestrus stage. In contrast, no difference was seen in the threshold Tre and steady state Tre at the end of exercise between proestrus and estrus stages. These values were higher at the higher work intensity. VO2 was also similar between the two stages, except in the second 5 min after the beginning of exercise, when VO2 was greater and Tre rose more steeply in the proestrus stage. These data indicate that deep body temperature during exercise is regulated at a certain level depending on the work intensity and is not influenced by the estrus cycle.

Animals↗
PubMed1987

Steroid-independent endogenous opioid peptide suppression of pulsatile luteinizing hormone release between estrus and diestrus in the rat estrous cycle.

We have previously demonstrated an absence of ovarian steroid negative feedback on pulsatile luteinizing hormone (LH) release between estrus and early diestrus 1 (D1) in the rat estrous cycle. The object of the present study was to determine if there was a steroid-independent endogenous opioid peptide (EOP) suppression of pulsatile LH release in this same 24-h interval, and if so, which parameter(s) of pulsatile LH release were affected. Rats were bled on estrus, or 24 h following sham ovariectomy (OVX), or OVX at 08.30-10.00 h on estrus. At the time of bleeding all rats were infused i.v. for 4 h either with 0.9% saline (0.5 ml/h) or naloxone (0.005, 0.05, 0.5, or 2 mg/kg/h). At 1 h after the infusion began, rats were bled for 3 h (40 or 50 microliters whole blood/5 min) between 09.30 and 12.30 h. Mean blood LH levels increased between estrus and early D1 due to increases in LH pulse amplitude and frequency. OVX on estrus decreased plasma levels of estradiol and progesterone 24 h later, but did not augment the increase in pulsatile LH release. However, naloxone infusion augmented the increase in pulsatile LH secretion in sham ovariectomized rats in a dose-dependent fashion. While infusion of 0.005 or 0.05 mg/kg/h had no effect, 0.5 or 2 mg/kg/h increased blood LH levels by increasing both LH pulse amplitude and frequency. The stimulatory effect of naloxone on pulsatile LH release was blocked by simultaneous infusion of morphine, demonstrating that the effect was mediated by EOP receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Persistent vaginal estrus and serum hormones after chlordecone (kepone) treatment of adult female rats.

The effects of chlordecone on vaginal estrus and neuroendocrine responses were examined in adult ovariectomized and intact females. Persistent vaginal estrus was seen in females given 50 mg/kg or more of chlordecone. The development of vaginal estrus was similar to that seen in ovariectomized females after treatment with estrogen. Since chlordecone is known to have estrogen-like effects on the reproductive system, the persistent vaginal estrus probably results from this estrogen-like action and chlordecone's long half-life in the organism. Neuroendocrine effects of chlordecone also resembled, to some degree, estrogen's effects on pituitary secretions. Chlordecone increased serum prolactin and decreased serum luteinizing hormone (LH) in ovariectomized females 30 to 36 hr after a single exposure to 50 mg/kg of the pesticide. Basal LH levels were not altered in intact females, but the proestrous LH surge was suppressed by 36 hr after treatment. Both basal and proestrous levels of prolactin were suppressed. Unlike the effects of estrogen, serum follicle stimulating hormone was not altered by chlordecone. These results indicate an effect on the hypothalamic pituitary axis by chlordecone treatment and offer a possible explanation for the reduced fertility seen in adult females after chlordecone exposure. However, blockage of the proestrous LH surge was not obligatory for the appearance of vaginal estrus. Although chlordecone produced peripheral changes in the vaginal smear pattern as well as neuroendocrine alterations, the peripheral changes were not always indicative of the neuroendocrine events.

Animals↗