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PubMed1986

Morphometric analysis of cell types in the ovine corpus luteum throughout the estrous cycle.

The cellular composition of ovine corpora lutea obtained during the early (Day 4), mid (Days 8 and 12), and late (Day 16) stages of the estrous cycle was determined by morphometric analysis. Individual corpora lutea were collected via midventral laparotomy from a total of 19 ewes. A center slice from each corpus luteum was processed for electron microscopy and subsequent morphometric analysis of the numbers and sizes of steroidogenic and nonsteroidogenic cells. Luteal weight progressively increased throughout the estrous cycle (p less than 0.05). Corpora lutea collected on Day 16 were assigned to one of two subgroups on the basis of gross appearance and weight: nonregressed (NR, 542 +/- 25 mg) or regressed (R, 260 +/- 2 mg). There were no significant changes in the proportion of the corpus luteum occupied by small luteal cells (19 +/- 2%) or large luteal cells (36 +/- 1%) throughout the estrous cycle. The total number of steroidogenic cells per corpus luteum increased from 21.8 +/- 3.7 (X 10(6)) on Day 4 to 61.7 +/- 5.4 (X 10(6)) on Day 8 (p less than 0.05) and remained elevated thereafter. The number of small luteal cells was 10.0 +/- 2.7 (X 10(6)), 39.7 +/- 1.4 (X 10(6)), 46.1 +/- 5.8 (X 10(6)), 49.0 +/- 13.7 (X 10(6)), and 29.9 +/- 8.6 (X 10(6)) on Days 4, 8, 12, 16 (NR), and 16 (R), respectively (p less than 0.05, Day 4 vs. Days 8, 12, 16 NR). In contrast, the number of large luteal cells was 11.8 +/- 1.5 (X 10(6)) on Day 4 and did not vary significantly during the remainder of the estrous cycle. The numbers of nonsteroidogenic cell types increased (p less than 0.05) from Day 4 to Day 16 (NR) but were decreased in regressed corpora lutea (Day 16 R). Regression was characterized by a 50% decrease (p less than 0.05) in the total number of cells per corpus luteum from 243 +/- 57 ( X 10(6)) on Day 16 (NR) to 125 +/- 14 ( X 10(6)) on Day 16 (R) (p less than 0.05). Small luteal cells remained constant in volume throughout the entire estrous cycle (2520 +/- 270 microns 3), whereas large luteal cells increased in size from 5300 +/- 800 microns 3 on Day 4 to 16,900 +/- 3300 microns 3 on Day 16 (NR) (p less than 0.05). In summary, small luteal cells increased in number but not size throughout the estrous cycle, whereas large luteal cells increased in size but not number.

Animals↗
PubMed1985

Steroid hormones and prolactin in porcine follicular fluid in estrous cycle and early pregnancy.

Concentrations of progesterone (P4), estradiol 17-beta (E2), testosterone (T) and prolactin (PRL) were estimated by RIA in porcine follicular fluid (FF) on 5th, 8th, 13th, 17th and 20th day of the estrous cycle and on 18th and 28th day of pregnancy. The highest P4 and E2 concentrations were found on 20th day of the estrous cycle. The P4 level measured on that day differed (P less than 0.05) from the levels on 5th, 13th and 17th day and E2 level on 20th day was different from the levels on remaining days of the estrous cycle, i.e. 5th, 8th, 13th and 17th. In pregnancy, concentrations of these steroids were much lower (P less than 0.05) compared to 20th day of the estrous cycle. No differences were found in T levels neither in estrous cycle nor in pregnancy. PRL concentration was at the lowest level on 5th day of the estrous cycle and it was different (P less than 0.05) from the concentrations on 8th day of the cycle and on 18th day of pregnancy (P less than 0.05). PRL content found on 28th day of pregnancy was lower (P less than 0.05) than on 18th day.

Animals↗
PubMed2004

Rat estrous cycle influences the sexual diergism of HPA axis stimulation by nicotine.

We previously reported that female rats had significantly greater hypothalamic-pituitary-adrenal (HPA) axis responses to cholinergic stimulation by nicotine (NIC) than did male rats. Females in defined estrous cycle stages, however, were not studied because of sample size limitations. We further explored this finding by determining HPA axis responses to two doses of NIC in female rats (N = 101) during different estrous cycle stages, and in males (N = 69). NIC doses were: 0.3 mg/kg, which provided the greatest female-male difference in the earlier study, and 0.5 mg/kg, which stimulated the HPA axis similarly in the two sexes. Plasma AVP, ACTH, and corticosterone were measured. Proestrous and estrous females had higher ACTH responses to NIC (0.3 mg/kg) compared to metestrous and diestrous females, and compared to males. ACTH responses to NIC (0.5 mg/kg) were similar, regardless of estrous cycle stage or sex. Males had higher AVP responses to both NIC doses compared to females in all estrous cycle stages. Corticosterone responses followed the ACTH responses, except that females in all estrous stages started from a higher corticosterone baseline compared to males. These results are similar to our earlier findings across the estrous cycle with non-specific cholinergic stimulation by physostigmine and suggest that the nicotinic system contributes to the differential HPA axis responses to cholinergic challenge across the estrous cycle.

Acetylcholine↗
PubMed2003

Sleep in female mice: a strain comparison across the estrous cycle.

STUDY OBJECTIVE: Studying inbred strains of mice has proven useful in uncovering genetic variation in the expression of sleep patterns. However, although genetic influence on many behaviors has been shown to be gender specific, to date, sleep patterns in different strains of female mice have not been reported. In order to perform such studies in female mice, the estrous cycle must be taken into account in view of the effects of reproductive hormones on sleep. The aim of this study was thus to determine sleep patterns in female mice of different inbred strains over the estrous cycle. DESIGN: Three strains of mice were used. Vaginal smears were performed to determine the estrous cycle stage; electroencephalographic and electromyographic activity, as well as body temperature and locomotor activity collected during a full estrous cycle, were analyzed. MEASUREMENTS AND RESULTS: We report a major impact of the genetic background in the regulation of non-rapid eye movement sleep over a 24-hour period and clear strain differences in rapid eye movement sleep distribution over the light-dark cycle. In contrast, the estrous cycle had less influence on non-rapid eye movement sleep and rapid eye movement sleep, and these effects were dependent on the genotype of the mice. CONCLUSIONS: Sleep regulation in female mice is influenced primarily by genetic background and, to a lesser extent, by hormonal variations associated with the estrous cycle.

Animals↗
PubMed2007

Estrous cycle effects on behavior of C57BL/6J and BALB/cByJ female mice: implications for phenotyping strategies.

Systematic behavioral phenotyping of genetically modified mice is a powerful method with which to identify the molecular factors implicated in control of animal behavior, with potential relevance for research into neuropsychiatric disorders. A number of such disorders display sex differences, yet the use of female mice in phenotyping strategies has been a rare practice because of the potential variability related to the estrous cycle. We have now investigated the behavioral effects of the estrous cycle in a battery of behavioral tests in C57BL/6J and BALB/cByJ inbred strains of mice. Whereas the performance of BALB/cByJ female mice varied significantly depending on the phase of the estrous cycle in the open field, tail flick and tail suspension tests, the behavior of C57BL/6J females, with the exception of the tail suspension performance, remained stable across all four phases of the estrous cycle in all of the tests including open field, rotarod, startle reflex and pre-pulse inhibition, tail flick and hot plate. We also found that irrespective of the estrous cycle, the behavior of C57BL/6J females was different from that of BALB/cByJ groups in all of the behavioral paradigms. Such strain differences were previously reported in male comparisons, suggesting that the same inter-group differences can be revealed by studying female or male mice. In addition, strain differences were evident even for behaviors that were susceptible to estrous cycle modulations, although their detection might necessitate the constitution of large experimental groups.

Analysis of Variance↗
PubMed1994

Regulation of gamma-aminobutyric acidB (GABAB) receptors in cerebral cortex during the estrous cycle.

We examined binding of the GABAB receptor agonist baclofen to brain synaptic membranes as a function of the natural variations in gonadal steroids that occur during the estrous cycle of the adult rat. We found that the binding of baclofen to neocortical membranes varied systematically as a function of the estrous cycle, with the lowest binding occurring during the estrus stage. Binding to archicortical (hippocampal) and hypothalamic preparations also varied with the estrous cycle, except that the lowest level of binding in these latter cases occurred during the diestrus stage. The variation of [3H]baclofen binding during the estrous cycle was different with respect to the binding of [3H]muscimol, an agonist for GABAA receptors, and [3H]8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), an agonist for serotonin 5-HT1A receptors that shares similar G proteins and effectors with GABAB receptors. Saturation binding studies of cortical GABAB receptors showed that apparent receptor density (Bmax) rather than affinity (Kd) best accounted for the change in binding during the estrous cycle in that Bmax, like total specific binding, was at a minimum during the estrus stage. The robust regulation of GABAB receptors in neocortex was unexpected and its functional significance is at present unknown. However, the correlation of the menstrual cycle with mood and other behavioral changes, and the correlations of the estrous and menstrual cycles with seizure susceptibility, may somehow depend upon hormonal regulation of transmitter systems such as the one we have observed here.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1989

Systemic progesterone concentration following human chorionic gonadotropin administration at various times during the estrous cycle in beef heifers.

In Trial 1, 26 heifers were allotted randomly to a control group or one of four groups to receive a single injection of 3,000 IU hCG on d 1, 4, 7 or 10 of an estrous cycle. Heifers next completed a nontreated cycle, and at their third estrus were reallotted to one of the five groups described previously. Estrous cycle length was extended in cycle 1 but was not altered during the nontreated cycle or in cycle 3. Administration of hCG on d 4 or 7 increased (P less than .05) mean serum progesterone (P4) over the first 16 d of the estrous cycle by .9 and .8 ng/ml, respectively. In Trial 2, 23 heifers were allotted randomly to one of two groups to receive a placebo or a single injection of 3,000 IU hCG on d 4 of an estrous cycle. Heifers were inseminated artificially at subsequent estrus. On d 4 postbreeding, treatments were repeated. Administration of hCG on d 4 of the prebreeding estrous cycle increased (P less than .05) mean P4 over the first 16 d by .9 ng/ml, whereas mean P4 over the first 16 d postbreeding was not affected by a second injection of hCG on d 4 postbreeding. Administration of hCG increased (P less than .05) first-service pregnancy rate (92 vs 55%). In conclusion, progesterone concentrations were enhanced by hCG given on d 4 or 7 of the estrous cycle, and pregnancy rate was increased when hCG was administered both on d 4 of the prebreeding cycle and d 4 postmating.

Animals↗
PubMed1988

Uterine steroid hormone receptors during the estrous cycle and during hibernation in the Turkish hamster (Mesocricetus brandti).

The Turkish hamster is a long-day breeder that hibernates for 4-5 mo if exposed to a short-day, cold environment. The objective of this study was to assess the uterine responsiveness of the hibernating animal to ovarian steroids. Our approach was 1) to characterize and determine uterine estrogen (E) and progesterone (P) receptors (R) during hibernation as compared to the levels observed in cycling females that had terminated hibernation, and 2) to assess the responsiveness of the uterus to E during hibernation by its ability to induce uterine P receptor. Females were exposed to short days (10L:14D) for 2 mo and then were placed in a cold-room (10L: 14D, 6 +/- 1 degrees C). After 2 or 4 mo in the cold, hibernating animals were killed and uterine steroid receptors were determined by 3H-steroid binding assay. Uterine receptors were also determined in cycling Turkish hamsters on each morning of the estrous cycle. Values for uterine receptors (pmol/g tissue, n = 4-6) during the estrous cycle (estrus, diestrus I, diestrus II, proestrus) were: 4.3 +/- 0.78, 3.9 +/- 0.19, 4.1 +/- 0.25, 3.7 +/- 0.5 for cytosolic ER; 36.6 +/- 5.8, 32.2 +/- 6.8, 36.3 +/- 1.5, 54.4 +/- 1.9 for cytosolic PR; 0.59 +/- 0.11, 0.54 +/- 0.07, 1.06 +/- 0.05, 1.42 +/- 0.17 for nuclear ER. Hibernating (torpid) animals sampled after 2 mo in the cold showed a significant (p less than 0.05) depression of cytosolic ER (2.6 +/- 0.12, n = 5) and cytosolic PR (19.0 +/- 2.6, n = 8) as compared to any day of the estrous cycle.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Estrous cycle variations in levels of cholecystokinin immunoreactivity within cells of three interconnected sexually dimorphic forebrain nuclei. Evidence for a regulatory role for estrogen.

The central part of the medial preoptic nucleus (MPNc), the encapsulated part of the bed nucleus of the stria terminalis (BSTe), and the posterodorsal part of the medial nucleus of the amygdala (MeAp) are all though to be involved in the neural control of female reproductive behavior, as well as other neuroendocrine mechanisms. Although the developmental importance of gonadal steroids during the perinatal period on these sexual dimorphisms is well known, an understanding of possible activational effects on these cell groups of circulating gonadal steroids in the adult is less clear. In the present study we evaluated the number of cholecystokinin (CCK)-immunoreactive cells present within MPNc, BSTe, and MeAp of regularly cycling female rats over the estrous cycle. In addition, the effects of ovariectomy and estrogen replacement on CCK staining were also examined. The number of CCK-immunoreactive cells within each cell group varied over the estrous cycle with the fewest cells present in animals sacrificed while in diestrus. Proestrous female rats showed a greater number of cells within each nucleus, while intermediate numbers were found for animals in estrus. These changes appear to be due, at least in part, to changes in levels of circulating estrogen, since subcutaneous implants of estradiol prevented the decline in the number of CCK-stained cells within MPNC, BSTe, and MeAp that was seen in untreated, ovariectomized female rats. Thus, the present findings support the hypothesis that levels of CCK within cells of these three sexually dimorphic cell groups are regulated by circulating gonadal steroids within a physiologically relevant time frame and may possibly contribute to the activation of female reproductive behavior as well as other neuroendocrine functions.

Amygdala↗
PubMed1988

Variations of liver prolactin receptors during the estrous cycle in normal rats and in the genetically hypoprolactinemic IPL nude rat.

Ovine prolactin (oPRL) binding to liver membranes was studied during the estrous cycle in normal and in genetically hypoprolactinemic rats. Serum levels of hormones were measured by radioimmunoassay and prolactin (PRL) binding was determined using 125I-ovine PRL in the 100,000 X g pellet. Scatchard plots obtained were curvilinear throughout the estrous cycle in the normal rat. They were analyzed in reference to the co-operativity model and to the Hill model which give the factor delta and Hill's coefficient (nH), respectively. During the estrous cycle, delta values varied from 3.77 +/- 0.66 on the day of estrous to 13.48 +/- 1.34 on the day of proestrus at 16.00 h. At the same time, nH were 0.97 +/- 0.033 on the day of estrus and 0.72 +/- 0.025 on the day of proestrus at 16.00 h. On the other hand, the number of PRL receptors did not change significantly throughout the estrous cycle. Moreover, the dissociation of 125I-oPRL from its receptor was accelerated by the presence of native ovine oPRL. These results suggest the presence of a negative co-operativity which reached a maximum on the day of proestrus in the normal rat. This co-operativity during the estrous cycle was not found in liver from genetically hypoprolactinemic (IPL nude) rats, which present a total absence of lactation. The delta values did not vary significantly and were 6.52 +/- 1.30 on the day of estrus and 4.41 +/- 0.52 on the day of proestrus at 16.00 h. The difference between the two rat strains was statistically significant on the day of proestrus at 16.00 h for both delta and nH values.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

Substance P and neurokinin A variations throughout the rat estrous cycle; comparison with ovariectomized and male rats: I. Plasma, hypothalamus, anterior and posterior pituitary.

The concentrations of Substance P and Neurokinin A were measured in plasma, and the hypothalamo-pituitary complex of 4-day-cycling female, ovariectomized and male rats. Estrous cycle-related fluctuations were recorded for these two neurokinins. The patterns of plasma concentrations of Substance P and Neurokinin A, however, were not similar throughout the rat estrous cycle. The plasma concentration of Substance P increased on proestrus at 19.00 hr, while Neurokinin A decreased. The plasma concentration of Substance P was positively correlated with plasma 17 beta-estradiol levels. In the ovariectomized rat, the absence of ovarian steroids led to low levels of plasma Neurokinin A, but the plasma concentration of Substance P did not show any change as compared to the estrous cycle. In the male rat, a similar observation was made in the presence of a testosterone environment. The largest variations in tissue concentration of both peptides were observed in the anterior pituitary. Substance P and Neurokinin A contents were higher throughout the proestrous day than the 3 other days. However, the level fell at 18.00 hr on proestrus, and there were similar falls in the hypothalamic contents of Substance P and Neurokinin A at 19.00 hr. In the ovariectomized rat, with no gonadal steroids, the hypothalamic and/or anterior pituitary levels of Substance P were in the same range as during the estrous cycle. However, the hypothalamic levels of Neurokinin A were lower and Neurokinin A was undetectable in the anterior pituitary. Substance P and Neurokinin A concentrations in the posterior pituitary were stable throughout the estrous cycle, with the exception of rises for both peptides on estrous day. Substance P levels were much lower in ovariectomized and male rats. These results describe large fluctuations in hypothalamic and pituitary Substance P and Neurokinin A contents through the estrous cycle in the female rat. They also strongly suggest the involvement of gonadal steroids in the differential regulation of Substance P and Neurokinin A in the female and male rat.

Animals↗
PubMed1989

N-methyl-aspartic acid lesions of the arcuate nucleus in adult C57BL/6J mice: a new model for age-related lengthening of the estrous cycle.

We report a new effect of the excitotoxin N-methyl-aspartic acid (NMA) on adult mice. Besides confirming cell loss in the arcuate nucleus of animals treated as adults, we also observed lengthened estrous cycles. Cycling female C57BL/6J mice were treated with subcutaneous injections of NMA and estrous cycles monitored for 30 days. NMA treatment lengthened average estrous cycle length by 1 day, to 5.6 days. The elongated cycles were due to an increase in the frequency of 5- and 6-day cycles at the expense of 4-day cycles. This effect was observed in mice aged 4 and 7 months; however, 10-month-old mice had irregular cycles and a higher mortality rate following NMA, which precluded cycle analysis. NMA caused a region-specific 30-45% cell loss in the rostral portions of the arcuate nucleus; no cell loss was detected in the adjacent ventromedial nucleus. Possible neuronal substates for NMA lesions, as analyzed by in vitro receptor autoradiography for glutamate receptor subtypes, include a high density of kainate receptors in the arcuate nucleus; there was little specific binding of ligands to NMDA and quisqualate receptors. Consistent with the regional pattern of cell loss, little specific binding of any glutamatergic ligand was observed in the VMN. NMA caused weight gain in all age groups. Serum LH and PRL were unaffected by NMA. The transition from 4-day to 5- and 6-day estrous cycles produced by NMA treatment mimics the early age-related changes in estrous cycle patterns in rodents. This new model will be useful in analyzing the contributions of neuroendocrine changes in the arcuate nucleus to reproductive senescence.

Aging↗
PubMed1989

Evaluation of the ability of altrenogest to control the equine estrous cycle.

In our experience, altrenogest has not always been able to exert predictable control over the estrous cycle of the mare. Therefore, we examined 12 mares that were treated with altrenogest to identify reasons for its failure to control the estrous cycle. The mares were fed altrenogest for 15 to 20 days and were examined for follicle development, ovulation, and corpus luteum formation during treatment. Through the use of real-time ultrasonography and radioimmunoassay for progesterone, we concluded that altrenogest was unable to suppress the growth of follicles to preovulatory size in some mares, leading to ovulation during treatment or earlier than expected after the end of treatment. In addition, altrenogest did not appear to shorten the life-spans of the corpora lutea that were formed during treatment; in 4 mares, this resulted in the persistence of corpora lutea after the end of the suggested 15-day periods of treatment. The latter findings led us to suggest that if a luteolytic dose of prostaglandin had been given at the end of altrenogest treatment, there would have been improved control over the estrous cycle. The results of our study confirmed our clinical impressions that altrenogest may be satisfactory to control the equine estrous cycle under some circumstances, but it should not be used when precise control over ovulation is required.

Animals↗
PubMed2005

The effect of active immunization against inhibin on gonadotropin secretions and follicular dynamics during the estrous cycle in cows.

The hypothesis of the present study is that active immunization of cows against inhibin would neutralize endogenous inhibin, increase circulating levels of follicle stimulating hormone, and subsequently affect follicular dynamics and the ovulation rate during the estrous cycle. Thirteen cows were immunized against inhibin alpha-subunit and, 6 cows were immunized with a placebo. Both groups were given 4 booster immunizations 7, 14, 21, and 34 weeks after the primary injection. Ovaries were examined daily after the 2nd, 3rd, and 4th booster immunizations by transrectal ultrasonography for 25 days. After the 4th booster immunization, blood samples were collected daily for one complete estrous cycle to measure FSH and LH. The results showed that the immunized cows generated antibodies against inhibin, and that they had higher FSH levels compared with the controls. The number of follicular waves during the estrous cycle was higher in the immunized cows (3 or 4 waves) than in the controls (2 or 3 waves). Moreover, the immunized cows had a greater number of follicles during the estrous cycle compared with the control cows. The maximum number of follicles was 14.8 +/- 1.7 vs 5.4 +/- 0.2 in inhibin-immunized and control cows, respectively, during the first follicular wave and 13.9 +/- 1.9 vs 5.6 +/- 0.7, respectively, during the ovulatory wave. Multiple ovulations were increased in the immunized cows. However, the ovulation rate varied greatly in the immunized animals. In conclusion, immunization against inhibin increased FSH secretions during the estrous cycle in the cows. Moreover, the immunized cows had a greater number of follicular waves during the estrous cycle and a greater number of follicles, and this could be used as a potential source of oocytes for use in IVF/embryo transfer programs.

Animals↗
PubMed1985

Effect of Ca2+ on the binding characteristics of muscarinic receptors in rat adenohypophysis--variation during the estrous cycle.

The effect of Ca2+ on the biochemical characteristics of muscarinic receptors in the adenohypophysis of male and female rats at the various stages of the estrous cycle was investigated in binding experiments using the specific muscarinic antagonist N-methyl-4-piperidyl benzylate ( [3H]-4NMPB) and the muscarinic agonist oxotremorine. By using Ca2+ chelators such as EGTA, and Ca2+ channel blockers such as D-600, we showed that Ca2+ profoundly alters the binding characteristics of both antagonists and agonists to the muscarinic receptors. In female rats the effect of Ca2+ on antagonist binding is mainly on the maximal binding capacity of the receptors, while changes in the dissociation constants are much more moderate. The effect is expressed in the ability of Ca2+ to expose or to eliminate binding sites as a function of the estrous cycle. In agonist binding, the presence of Ca2+ has a pronounced effect on the proportion of high-affinity binding sites, which parallels the changes induced in antagonist binding throughout the estrous cycle. Interestingly, the natural progression of the cycle from diestrus 2 to the estrous stage undergoes a change identical to that occurring in vitro upon Ca2+ removal. D-600 can completely block the effect of Ca2+ on the binding of both [3H]-4NMPB and oxotremorine. The concentration of D-600 required in order to induce such blocking is also dependent on the estrous cycle. It appears that the progression of the estrous cycle is accompanied by changes in the muscarinic receptors which may in turn be coupled to Ca2+ channels.

Animals↗
PubMed1999

PGE receptor characteristics on porcine luteal cells during the estrous cycle and early pregnancy.

This study examined the affinities and concentrations of prostaglandin E (PGE) receptors on porcine luteal cells during the estrous cycle and early pregnancy. Corpora lutea (CL) were obtained from nonpregnant gilts at days 9 (n = 4), 12 (n = 3), and 14 (n = 6); three gilts possessed red, vascular CL and three gilts had white nonvascular CL) of the estrous cycle, and days 9 (n = 4), 12 (n = 3), 14 (n = 5), and 30 (n = 5) of pregnancy. The CL were dissociated enzymatically to disperse single cells and the red blood cells were removed by elutriation. The luteal cells were assayed for specific PGE binding by displacement analysis with use of [3H] PGE2 and varying concentrations of unlabeled PGE2. The specific binding of [3H] PGE2 to luteal cells decreased (p < 0.05) from days 9 to 14 of the estrous cycle, but only decreased (p < 0.05) from days 9 to 12 of pregnancy. Specific binding was higher (p < 0.05) on day 14 of pregnancy than the comparable stage of the estrous cycle. The affinities of PGE receptors decreased (p < 0.05) only on the luteal cells dissociated from red, vascular CL of day 14 nonpregnant gilts compared with those of other days of the estrous cycle and pregnancy. The number of PGE receptors on porcine luteal cells was similar (p > 0.05) in pregnant and nonpregnant gilts, but decreased (p < 0.05) on days 12-14 postestrus. During early pregnancy, it was evident that high affinity PGE receptors are sustained on porcine luteal cells; however, the role of the PGE receptors in maternal recognition of pregnancy remains speculative.

Animals↗
PubMed1984

Stage of estrous cycle, time of insemination, and seasonal effects on estrus and fertility of Holstein heifers after prostaglandin F2 alpha.

Stage of estrous cycle, time of insemination, and season of the year were examined for their influence on estrus and fertility of 223 Holstein heifers after prostaglandin F2 alpha (treatment). Heifers treated during early stages (days 5 to 8) of the estrous cycle had shorter (by 11 h) and less variable intervals to estrus compared with treatment of heifers during late stages (days 14 to 16) of the estrous cycle. A greater proportion of heifers in the early cycle treatment (79/81, 97%) were in synchronous estrus (20-h period) after treatment compared with the late cycle treatment (71/86, 83%). Conception rates were lower when early cycle heifers were inseminated at 80 h after prostaglandin F2 alpha than when inseminated according to estrous detection and also lower as compared with late cycle heifers inseminated at 80 h. No differences in fertility were observed for late cycle heifers inseminated at 80 h compared with those inseminated according to estrous detection. Season of the year had no influence on intervals to estrus or on proportion of heifers expressing estrus after prostaglandin F2 alpha, regardless of stage of estrous cycle. Conception rate during winter, however, was higher in early but not late cycle heifers inseminated after prostaglandin F2 alpha, as compared with fall or spring. Variability of interval to estrus and of fertility after inseminations by appointment at 80 h appears to be due to stage of estrous cycle at time of prostaglandin F2 alpha treatment rather than season of the year.

Animals↗
PubMed1989

The effect of wheel running and the estrous cycle on energy expenditure in female rats.

In female rats, food intake and wheel running fluctuate with the estrous cycle, creating a state of oscillating energy balance. The effect of the estrous cycle on the energy expenditure of conventionally housed rats (S) and of rats given access to an activity wheel (A) was compared. Over 24 weeks, the weight gain of the groups was similar although the body fat content of A was 30 g lower than that of S at the end of the study. During the assessment of energy expenditure by indirect calorimetry estrous cycles were disrupted and food intake and wheel running reduced. However, a correlation between expenditure and wheel running was obtained from which the cost of activity was derived (21 kJ/kg/km) and from which data were extrapolated to normal circumstances. This revealed that A, running on average 6214 rev/day, expended approximately 64 kJ/day more than S. This they compensated for by increasing their food intake by 6 g/day (70 kJ/day). Over the estrous cycle wheel running was maximal at proestrus and minimal at metestrus--the reverse trend in food intake was observed. This cyclic difference in energy balance between metestrus and proestrus was estimated to be equivalent to 23% of the 'maintenance' requirement. Thus voluntary activity bears a marked impact on day to day energy balance but has little effect in the long-term since in the female rat intake is precisely regulated to meet expenditure.

Adipose Tissue↗