Variations in concentration of oxytocin and vasopressin in the paraventricular nucleus of the hypothalamus during the estrous cycle in rats

Oxytocin (OT) and arginine-8-vasopressin (AVP) were measured by radioimmunoassay in micropunched hypothalamic neurosecretory nuclei of estrous cycling female Sprague-Dawley rats. In the paraventricular nucleus (PVN): the concentration (pg/microgram protein) of OT was significantly higher in rats in diestrus than during proestrus, estrus, or metestrus, while the concentration during metestrus was significantly greater than in proestrus and estrus; the concentration of AVP was significantly lower in animals in estrus than during the other three stages; because the paraventricular OT levels dropped before proestrus, the AVP/OT ratio was significantly greater in animals in proestrus than in diestrus, metestrus, and estrus. In the supraoptic nucleus (SON) a similar trend was noted: the concentration of OT was highest during diestrus, and AVP was lowest during estrus, though neither was significantly different from other stages. Because the OT and AVP cycles in the SON were asynchronous, the ratio of AVP to OT was significantly higher in proestrus than in metestrus or diestrus and significantly greater in estrus than during diestrus. In contrast to these two areas, peptide concentrations did not vary significantly across the estrous cycle in other sites of nonapeptide synthesis, i.e. the anterior commissural nucleus (ACN) and the suprachiasmatic nuclei (SCN).     

Inhibition of estrus and corpora lutea function with Norgestomet

Forty-five nonpregnant, nonlactating, Angus and Brangus cows were utilized to determine how long a Norgestomet ear implant would inhibit estrus when administered at various stages of an estrous cycle. All cows completed a nontreated estrous cycle to ensure normal cyclicity. At the second observed estrus (estrus = Day 1), cows were randomly allotted to be treated at metestrus (Day 3 or Day 4, n = 15); at diestrus (Day 9 or Day 10, n = 14); or at proestrus (Day 15 or Day 16, n = 16). All cows received a 2-ml intramuscular injection of 3 mg of Norgestomet accompanied by a 6-mg Norgestomet ear implant, which remained in situ for 21 days, or until individual cows were observed in estrus. Estrus was inhibited for a mean (+/- SEM) of 18.7 +/- 0.7, 19.9 +/- 0.8, and 17.0 +/- 0.8 days, respectively, when cows were treated at metestrus, diestrus, and proestrus (metestrus and diestrus vs proestrus; P < 0.05). Estrus was inhibited for an entire 21-day implantation period in 27, 50, and 38% of cows treated at metestrus, diestrus, and proestrus, respectively (P > 0.10). Norgestomet inhibited estrus in all cows for 11, 17, and 11 days after implantation when treatment was initiated at metestrus, diestrus, and proestrus, respectively (P > 0.10). These data indicate that a 6-mg Norgestomet ear implant effectively inhibits estrus in all cows for a maximum of 11 days, with some cows exhibiting estrus by Day 12 with the Norgestomet implant in situ.     

Prolactin receptors in the rat mammary gland. Change during the estrous cycle

Ovine prolactin (o-PRL) binding to mammary gland membranes was studied during the estrous cycle in the rat. Groups of rats were decapitated throughout the 4-day estrous cycle at 10 h00 on the days of diestrus I, diestrus II and estrus and at 10 h00, 12 h00, 16 h00 during the day of proestrus. Daily vaginal smears were taken to determine the stage of the estrous cycle which was also controlled by PRL and LH serum levels. Prolactin receptors were quantified in the 100 000 g pellet. For one Scatchard analysis, mammary gland membranes from 5 animals were pooled. Results given are the mean of 4 or 5 pools. Results obtained showed that the apparent affinity constant (KA) remained unchanged during the days of diestrus II and at all the times studied of proestrus and showed a slight but significant decrease on the days of estrus and diestrus I (or metestrus). The binding capacity did not vary from the day of diestrus II to the proestrus 16h00 (11.3 +/- 2.8 fmoles/mg protein) but sharply increased on the day of estrus (190.4 +/- 35.9 fmoles/mg protein). Binding capacity remained elevated on the day of diestrus I. This increase of PRL receptors on the day of estrous would appear to be an important step in preparing mammary gland for pregnancy and lactation.     

Pain threshold variations in female rats as a function of the estrus Cycle

In this study, the response of female rats in different phases of the estrus cycle to nociceptive stimulation was evaluated using thermal (hot plate and tail immersion) and chemical (formalin) tests. In the hot plate test, the paw licking latency fell significantly (p < 0.05) in the metestrus and diestrus phases compared with the proestrus and estrus phases. The observations in the tail immersion test also followed the same pattern. The significant reductions in the paw licking and tail withdrawal latencies due to a lowered threshold denote an increase in pain sensitivity in the metestrus and diestrus phases. In the formalin test, the licking time fell significantly from the metestrus to the diestrus phase compared with the proestrus and estrus phases, the reduction in this test which was due to an increased threshold connotes a decrease in pain sensitivity. The results therefore seem test dependent. In conclusion, pain threshold in female rats depends on the estrus state. Keywords: Pain threshold, Variation, Estrus cycle.     

Inhibin secretion during the rat estrous cycle: relationships to FSH secretion and FSH beta subunit mRNA concentrations

Serum inhibin and FSH and FSH beta subunit mRNA levels were measured at 3h intervals throughout the 4 day estrous cycle in female rats and hourly between 1000 and 2400 h of proestrus. On proestrus, serum inhibin concentrations fell during the late morning-early afternoon, then increased transiently during the late afternoon gonadotropin surges. Inhibin levels decreased during the late evening of proestrus, coincident with the FSH surge-related rise in FSH beta mRNA levels. Serum inhibin remained relatively stable during estrus and early metestrus, but rose during the late evening of metestrus and remained elevated until early diestrus. FSH beta mRNA levels were elevated on late estrus and early metestrus and declined during the evening of metestrus as serum inhibin levels increased. These data show that concentrations of serum inhibin change during the estrous cycle and that a general inverse relationship exists between serum inhibin and FSH levels and FSH beta mRNA concentrations in the pituitary. This suggests that inhibin may inhibit FSH beta gene expression and FSH secretion during the 4 day cycle in female rats.     

Dynamics of messenger RNAs encoding inhibin/activin subunits and follistatin in the ovary during the rat estrous cycle

Quantitative changes in ovarian inhibin/activin subunit and follistatin mRNAs during the rat estrous cycle were examined by ribonuclease protection assay using digoxygenin-labeled RNA probes. Levels of ovarian inhibin alpha subunit mRNA remained low throughout estrus, metestrus, and diestrus; abruptly increased on the morning of proestrus; then rapidly decreased when the primary gonadotropin surge occurred. A similar changing pattern was observed in inhibin/activin beta(A) subunit mRNA. On the other hand, inhibin/activin beta(B) subunit mRNA showed a different changing pattern. Levels of beta(B) subunit mRNA remained constant during metestrus and diestrus, abruptly decreased on the afternoon of proestrus, then quickly recovered from the nadir by 1100 h on estrus. Throughout the rat estrous cycle, especially during the periovulatory period, alpha subunit mRNA levels were considerably higher than beta(A) and beta(B) subunit mRNA levels. In addition, changes in plasma concentrations of inhibin A and inhibin B were very similar to that in ovarian beta(A) and beta(B) subunit mRNA levels, respectively, with several-hour delays. These results suggest that levels of beta subunit mRNAs restrict secretion of dimeric inhibins. Levels of follistatin mRNA remained low from the midnight of metestrus to the midnight of diestrus, then increased until initiation of the primary gonadotropin surge. Thereafter, follistatin mRNA decreased, reached the nadir at 0200 h on estrus, then increased abruptly at 1100 h on estrus. Afterward, follistatin mRNA levels remained high until the morning of metestrus. The changing pattern of ovarian follistatin mRNA was similar to, and preceded, the changes in plasma concentrations of progesterone, suggesting that ovarian follistatin may modulate progesterone secretion during the rat estrous cycle.     

Atrial supersensitivity to noradrenaline in stressed female rats

Stress can change the responses to catecholamines in many tissues. The aim of this study was to investigate the influence of the estrous cycle on the sensitivity of right atria to noradrenaline in female rats subjected to acute swimming stress. Female Wistar rats in proestrus, estrus, metestrus or diestrus were submitted to a 50 min-swimming session. Immediately after the exercise, the rats were killed and their right atria were mounted for isometric recording of the spontaneous beating rate. Concentration-effect curves to noradrenaline were obtained before and after the inhibition of neuronal uptake with phenoxybenzamine (10 microM) and of extraneuronal uptake with estradiol (5 microM). Acute swimming stress did not change the right atrial sensitivity to noradrenaline in rats in estrus, metestrus and diestrus. However, swimming stress produced supersensitivity to noradrenaline in proestrus (pD(2) control: 7.14 +/- 0.03 vs. pD(2) swimming: 7.55 +/- 0.04; p<0.05). This supersensitivity was still observed after uptake inhibition. When catecholamine uptake was inhibited, the concentration-effect curve to noradrenaline was shifted to the left 2.5-fold in the proestrus control group and 1.7-fold in the proestrus stress group (p<0.05). In conclusion, the estrous cycle influenced the acute stress-induced atrial supersensitivity to noradrenaline.     

Opposite regulation of XIAP and Smac/DIABLO in the rat endometrium in response to 17β-estradiol at estrus

During rat estrous cycle, the endometrium proliferates in response to sex steroids and specific endometrial epithelial cells undergo apoptosis in absence of embryonic factors. The central executioner of apoptosis is a family of aspartic acid-specific cysteine proteases known as caspases. Smac/DIABLO is released from the mitochondria during apoptosis and its stimulation promotes caspases activation by neutralizing members of the inhibitor of apoptosis proteins (IAPs) family, such as X-linked inhibitor of apoptosis protein (XIAP). The aim of this study was to investigate the involvement of Smac/DIABLO and XIAP in the control of caspases activation in endometrium of cycling rats. Polyoestrus female rats were sacrificed at each stage of estrous cycle (diestrus, proestrus, estrus, and metestrus). Endometrial protein extracts were collected to perform Western Blot analysis. Alternatively, uterine horns were sectioned for immunohistochemistry (IHC). We and others showed previously the presence of apoptosis at estrus in rat uterine epithelium. In the present study, cleaved caspase-3, -6, and -7 fragments were detected at estrus. IHC confirmed that caspase-3 was present only in luminal and glandular epithelium at estrus. XIAP was highly expressed at estrus in both epithelial and stromal cells. In contrast, expression of Smac/DIABLO was elevated at diestrus, proestrus and metestrus but was minimal at estrus. Treatment of ovariectomized rats with 17β-estradiol induced XIAP expression and inhibited Smac/DIABLO protein expression in the endometrium. Cleaved caspase-3, -6, and -7 fragments increased in endometrial protein extracts following 17β-estradiol treatment. Expression of NF-κB and IκB proteins, and IκB phosphorylation status were detected in the endometrium but were not influenced by the estrous cycle. These findings suggest that Smac/DIABLO and XIAP are regulated differently and may play important roles in the regulation of endometrial cell fate. Moreover, this study confirms a key role for executioner caspases in the control of apoptotic processes at estrus in the rat uterus.     

小熊猫繁殖周期血清雌二醇和孕酮含量变化

为研究小熊猫繁殖周期血清雌二醇、孕酮含量变化规律,采用化学发光免疫分析法连续16 次测定了2只成体雌性小熊猫血清雌二醇和孕酮含量变化,历经发情间期、发情期和两次妊娠期;连续9次测定了7只小熊猫妊娠期的孕酮含量变化。结果:(1)发情间期,小熊猫血清雌二醇的水平一直维持在低水平(基础水平),进入发情前期,血清雌二醇水平明显升高,在发情期一直维持高水平,配种后迅速降至基础水平; (2)小熊猫血清孕酮含量在发情间期和发情期均维持在较低水平,直至发情期过后才出现升高,在妊娠期一直维持高水平,峰值出现在5 月;(3)发情的小熊猫不论妊娠与否,在妊娠期内血清孕酮含量均维持在高水平。研究表明:小熊猫血清雌二醇、孕酮含量变化能直接反映其繁殖规律,雌二醇对启动雌性小熊猫季节性繁殖起重要作用;在妊娠期内小熊猫血清孕酮含量升高不能作为判断小熊猫妊娠的标准;雌性小熊猫在妊娠期有假孕现象。     

Effect of estrous cycle phase on pain threshold in female white rats]

Pain thresholds and body resistance in female Wistar rats were determined during estrous cycle stages. The flinch and shuffle thresholds were increased on the 3rd day of measurement in diestrus and estrus but not in proestrus and metestrus as compared with the thresholds during the 1st day of recording. The thresholds decreased as of the 7th day to the 14th day. Daily threshold measurements raised the body resistance on the 7th day of recording. In contrast to the pain thresholds, the body resistance change had not a stage-dependent character.     

大鼠动情周期中生殖轴系微循环血量的变化

本文采用放射性生物微球技术,对雌性大鼠动情周期中丘脑下部-垂体-卵巢轴系的微循环血量进行了测量。结果指出,周期各期丘脑下部和垂体的血流量无显著差异(p>0.05)。卵巢血流量在动情后期最大,动情期最小,两期血流量的差异显著(p<0.02)。子宮血流量以动情后期最大,间情期仍维持在较高水平,动情期最小。动情后期和间情期与动情期比较均有显著差异(分别为p<0.01和P<0.05)。输卵管血流量动情期最大,动情前期最小,两期血流量的差异也有显著性(p<0.05)。由此表明,卵巢、子宫和输卵管血流量有明显的周期性波动。血流量的多寡与其生理机能状态和性激素的变化有关。     

Ovarian steroidogenic enzyme activities during the rat estrous cycle

We have correlated the concentrations of serum LH, estradiol and progesterone with the activities of 2 ovarian steroid biosynthetic enzymes during the rat estrous cycle. Ovarian 3 β-hydroxysteroid dehydrogenase isomerase (3-βHSD) activity decreased from 29 ± 6 nmol/mg protein/ min (mean ± SEM) in diestrus, to 7 ± 0.4 nmol/mg protein/min in late proestrus (p < 0.005), and subsequently increased to 36 ± 9 nmol/mg protein/min in metestrus (p < 0.01). Ovarian 17-hydroxylase (17-OH) activity decreased from early to late proestrus (3.3 ± 0.2 vs 2.2 ± 0.2 nmol/mg protein/min, p <0.0025), and subsequently increased to 3.9 ± 0.2 in metestrus (p<0.001). Serum LH, estradiol and progesterone peaked during proestrus, and reached a nadir during estrus. We conclude that the activities of 3-βHSD and 17-OH in the rat ovary vary markedly during the estrous cycle. These changes may underlie the pattern of steroid secretion characteristic of this process.     

Plasma concentration of progesterone and 17beta-estradiol of black-rumped agouti (Dasyprocta prymnolopha) during the estrous cycle

Plasma concentration of progesterone and 17beta-estradiol of black-rumped agouti (Dasyprocta prymnolopha) during the estrous cycle. The agouti is a game animal that have been raised in captivity for conservation and sustainability purposes. However, the management of wild animals in an intensive breeding system requires an assertive knowledge of its reproductive parameters, one of the most important features for production improvement. Besides, little information is available regarding changes in reproductive hormone profiles in agouti. The objective of this study was to evaluate the hormonal profile of progesterone and 17beta-estradiol during the estrous cycle of the agouti (Dasyprocta prymnolopha). The hormones were analyzed by radioimmunoassay. Blood samples were collected without sedation twice a week. The concentrations of progesterone were as follows: proestrus 0.78 +/- 0.39 ng/ml, estrus 2.83 +/- 2.34 ng/ml, metestrus 1.49 +/- 1.24 ng/ml, diestrus 3.71 +/- 1.48 ng/ml. In the estrous phase, an increase in the progesterone level was observed during a period of 24h. The average 17 beta-estradiol levels were as follows: proestrus 2 030.98 +/- 961.00 pg/ml, estrus 1 910.56 +/- 650.54 pg/ml, metestrus 1 724.83 +/- 767.28 pg/ml, diestrus 1 939.94 +/- 725.29 pg/ml. The current results suggest that the progesterone plasma concentration during the estrous cycle in the agouti has a similar increasing, stabilizing and decreasing pattern, as in domestic mammals. Agoutis have two phases of follicular development, as two periods of 17beta-estradiol peaks were observed, the first one in the metestrus and the second during the proestrus. Spontaneous ovulation seems to occur after the progesterone peak, possibly indicating that this hormone is associated with the ovulatory process. A more detailed investigation is needed for better understanding of how progesterone influences ovulation. Studies on the involvement of progesterone in follicular rupture can be carried out, using steroid biosynthesis inhibitors and observing the effect of this hormone on ovarian activity of proteolytic enzymes in the follicular wall.     

Estrous cycle fluctuations in aggressiveness of house mice

The purpose of this study was to determine whether interfemale, isolationinduced aggression in house mice varies over the phases of the estrous cycle. The results indicated that there were significant variations, with aggression being higher at proestrus and metestrus and lower at estrus and diestrus. Activity level showed fluctuations across the cycle similar to the pattern established by previous research. The results were interpreted in terms of possible adaptiveness.     

Patterns of follicular growth during the four-day estrous cycle of the rat

Female Sprague-Dawley rats underwent laporatomy during metestrus at 70 to 75 days of age or remained untreated to study the effects of surgical stress on follicular growth. Groups of rats were killed on each day of a 4-day estrous cycle, serial sections of the ovaries were prepared histologically and the number and size of follicles with one or more complete layers of cuboidal granulosa cells were determined. Since no differences due to surgery were found, the data were pooled by day of the estrous cycle (17 or 18 rats/day of cycle) for characterization and comparison of size distribution of follicles on different days of the estrous cycle. Follicles were classified as atretic or healthy and divided into groups by increments of 20 micron of diameter for graphing. Data were analyzed by analysis of variance and least squares means. Significant differences were found in the distribution of both healthy and atretic follicles among days of the estrous cycle. At least 21 follicles/ovary were recruited from less than 260 micron into greater than 260 micron in diameter between proestrus and estrus, and the follicles for ovulation were selected by diestrus. A greater number of growing follicles of 70 to 100 micron in diameter were present at diestrus. From the disappearance of follicles greater than 260 micron between estrus and proestrus, it appears that atresia is a very rapid process.     

Histomorphological Changes in the Reproductive Tract of Female Hemiechinus auritus collaris,Gray in Relation to the Estrous Cycle

The average length of the estrous period is 7.9 days in Hemiechinus auritus collaris. Follicular development takes place cyclically. Maximum atresia of follicles is noticed during metestrus. The corpus luteum is formed by the shrinkage of the remaining granulosa cells of the ovulated follicle. Maximum development of the corpus luteum is seen during the pregnancy. Histological changes in the uterus and vagina during the estrous cycle are described. There is a marked rise in the weight of the uterus and ovary during the proestrus phase of the cycle. The estrus phase is characterized by the signs of degeneration in the uterine epithelium. During metestrus degeneration and regeneration proceed together. Secretory activity is at a minimum and the lumina of the glands are empty during diestrus.     

Changes in the content and distribution of microtubule associated protein 2 in the hippocampus of the rat during the estrous cycle

The molecular mechanisms involved in the regulation of synaptic plasticity in the hippocampus during the estrous cycle of the rat are not completely understood. Because this process implicates changes in neuronal cytoskeleton organization, we analyzed the content of microtubule associated protein 2 (MAP2) and Tau in the hippocampus and the frontal cortex of the rat by Western blot, as well as the hippocampal distribution of MAP2 during the estrous cycle by immunohistochemistry. In the hippocampus the lowest content of MAP2 was found on diestrus day, and it significantly increased at proestrus. This increase was maintained on estrus and metestrus days. In the frontal cortex MAP2 content did not significantly change during the estrous cycle. In contrast, the content of Tau did not vary during the estrous cycle in either the hippocampus or the frontal cortex. The immunohistochemical analysis showed an increase in dendrite thickness and in dendritic branching in the CA1 region on proestrus day, as well as an aggregation of MAP2 in apical dendrites near to pyramidal somata on this day in comparison with diestrus. We suggest that changes in the content and neuronal distribution of MAP2 are involved in the structural changes that occur in the hippocampus of the rat during the estrous cycle, and that these variations are related to changes in estradiol and progesterone levels.     

Effect of methyl parathion formulation on estrous cycle and reproductive performance in albino rats

The animals were injected intraperitoneally with graded doses of methyl parathion at 1.5 to 3 mg/kg body weight for 15 days from the day of estrus. Results indicated that the methyl parathion treatment showed irregular estrous cycles, affect the duration of each estrous cycle, proestrus and diestrus were significantly changed in 2.5 and 3 mg treatment groups. But there was no significant change in the number and duration of each estrous cycle, duration of proestrus and diestrus in 1.5 and 2 mg methyl parathion treatment groups. However, there was a significant decrease in the duration of estrus, while there was no significant change in the duration of metestrus in all methyl parathion treatment rats when compared with those of the corresponding parameters of the control. There was no significant effect on number of live pups on day 1 and 5 except in 3 mg methyl parathion treatment group where it was significantly decreased. There was no significant change in reproductive indices like pregnancy, parturition, live birth and viability in all the methyl parathion treatment rats except the viability index in the highest dose.