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PubMed1997

Cytosolic estrogen receptor concentrations in the lumbosacral spinal cord fluctuate during the estrous cycle.

Estrogen responsive neurons have been anatomically identified with autoradiographic and immunohistochemical techniques and their distribution mapped in the lumbosacral spinal cord of female rats. Such neurons contain estrogen receptors (ERs). The present study was undertaken to: 1) quantify cytosolic estrogen receptor (ER) concentrations in the lumbosacral spinal cord and 2) determine if there is a relationship between cytosolic ER concentrations and fluctuations in serum estradiol (SE2) levels during the estrous cycle. Lumbosacral spinal segments were removed from intact cycling rats during the morning of proestrus, the afternoon of proestrus, and the morning of estrus, metestrus and diestrus. Trunk blood was collected at euthanasia and SE2 levels were determined using radioimmunoassay. Cytosolic ER concentrations were measured using a dextran-charcoal coated tube method. Concentrations of cytosolic ERs were low during estrus and metestrus, increased during diestrus with maximum concentrations during the afternoon of proestrus. These changes in ER concentrations paralleled SE2 levels measured in intact cycling animals; i.e., during estrus SE2 levels were low, but began to rise during metestrus, diestrus, and during the morning of proestrus with a maximum peak increase during the afternoon of proestrus. These data indicate there are fluctuations of cytosolic ER concentrations during the estrous cycle and that these changes coincide with changing SE2 concentrations suggesting that ER content is influenced by SE2.

Animals↗
PubMed1999

Definitive evidence for the existence of morphological plasticity in the external zone of the median eminence during the rat estrous cycle: implication of neuro-glio-endothelial interactions in gonadotropin-releasing hormone release.

Despite intense investigation, the demonstration of morphological plasticity in the external zone of the median eminence concerning the gonadotropin-releasing hormone system has never been reported. In this study, we investigate whether dynamic transformations of the gonadotropin-releasing hormone nerve terminals and/or tanycytes in the external zone of the median eminence of the hypothalamus occurred during the rat estrous cycle, by following individual gonadotropin-releasing hormone-immunoreactive nerve terminals on serial ultrathin sections observed by electron microscopy. Female rats were killed at 16.00 diestrus II (n = 3), i.e. when estrogen levels are basal and gonadotropin-releasing hormone release is low, and at 16.00 proestrus (n = 4), i.e. when estrogen levels peak and the preovulatory gonadotropin-releasing hormone surge occurs. Our results show that, in the median eminence obtained from proestrus rats, 12+/-2% of the gonadotropin-releasing hormone nerve terminals were observed to make physical contact with the parenchymatous basal lamina, i.e. the pericapillary space. In the median eminence obtained from diestrus II rats, no contacts were observed. On proestrus, numerous physical contacts between gonadotropin-releasing hormone nerve terminals and the basal lamina occurred by evagination of the basal lamina and/or by emerging processes from gonadotropin-releasing hormone nerve terminals. The quantification of the evagination of the basal lamina revealed that the basal lamina was at least twofold more tortuous in appearance during proestrus. These results demonstrate for the first time the existence of dynamic plastic changes in the external zone of the median eminence, allowing gonadotropin-releasing hormone nerve terminals to contact the pericapillary space on the day of proestrus, thus facilitating the release of the neurohormone into the pituitary portal blood.

Animals↗
PubMed1987

Preovulatory secretion of progesterone, luteinizing hormone, and prolactin in 4-day and 5-day cycling rats.

Timing of ovulation and changes in plasma progesterone, luteinizing hormone (LH), and prolactin (PRL) during periovulatory stages were determined in Holtzman rats exhibiting regular 4- or 5-day cycles under a daily artificial illumination from 0500 to 1900 h. The 5-day cycling rats ovulated between 0130 and 0930 h on estrus, whereas some of the 4-day cycling animals ovulated as early as about 0130 h and others as late as 1130 h on estrus. Onset time of preovulatory LH and progesterone surges was about 1500 h on proestrus in both the 4- and the 5-day cycling rats. Peak levels of plasma LH and progesterone were measured at 1700 to 1900 h on proestrus, while the first rises and peak values of plasma PRL were evident a few hours earlier than those of plasma LH in the rats with two cycle lengths. Plasma LH levels at 1900 h on proestrus as well as plasma progesterone levels at 1600 and 2300 h on proestrus and at 0130 and 0330 h on estrus were significantly lower in the 5-day cycling rats than in the 4-day cycling animals (p less than 0.05). In contrast, PRL levels from 1500 through 2300 h on proestrus remained consistently higher in 5-day cycling rats than in 4-day cycling rats, and significant differences in PRL levels between these rats were apparent at 1500, 1600, and 2100 h (p less than 0.05-0.01). Thus, these results demonstrate that the 5-day cycling rats exhibit the attenuated magnitude of LH surge accompanied by the augmented preovulatory PRL release, and that plasma progesterone levels reflect the magnitude of LH surge. A tentative working hypothesis concerning the etiology of the 5-day cycle has been proposed.

Animals↗
PubMed1995

Follicular and luteal progesterone play different roles synchronizing pituitary and ovarian events in the 4-day cyclic rat.

Administration of 4 mg of the antiprogestagen RU486 to 4-day cyclic rats during proestrus induced a 1-day shortening of the ovarian cycle, a reduction in ovulatory rate that was reversed by an injection of exogenous human (h)FSH in the evening of proestrus, and the absence of the LH-inhibiting effect of exogenous estradiol resulting in a 24-h advancement of the preovulatory LH surge. These effects were not present when RU486 was injected during estrus. RU486 injected during either proestrus or estrus increased serum levels of LH and estradiol-17 beta in diestrus and reduced the magnitude of the preovulatory surge of gonadotropins. Only rats treated with RU486 during estrus showed increased follicular size and acceleration of oocyte maturation on proestrous afternoon. These results demonstrate that in 4-day cyclic rats receiving an injection of RU486 during proestrus, the low ovulatory rate is a consequence of a reduced secondary FSH surge-induced follicular recruitment in the afternoon of estrus and that the shortening of the estrous cycle is the result of an advanced desensitization to the negative feedback of estradiol on LH secretion. Furthermore, since the administration of RU486 during proestrus blocks both follicular and luteal progesterone actions whereas injection during estrus blocks only luteal progesterone actions, we suggest that, in 4-day cyclic rats, the actions of progesterone during diestrus retard maturation of follicles via the lowering of serum LH concentrations and that the actions of progesterone in proestrous evening delay the desensitization to the negative estrogen feedback on LH secretion.

Animals↗
PubMed2002

Preservation of splenic immune functions by female sex hormones after trauma-hemorrhage.

OBJECTIVES: Immune functions are markedly depressed in males but not in proestrus females after trauma-hemorrhage. Nonetheless, it is unclear what role sex steroids play in the maintenance of immune function in females after trauma-hemorrhage. DESIGN: Prospective, controlled animal study. SETTING: University research laboratory. SUBJECTS: Eight-week-old female CBA/J mice. INTERVENTIONS: Mice underwent sham-ovariectomy or ovariectomy. Two weeks thereafter, ovariectomized and proestrus sham-ovariectomized mice were subjected to laparotomy (i.e., soft tissue trauma) and hemorrhagic shock (35 +/- 5 mm Hg for 90 mins, resuscitated) or sham operation. Splenocyte proliferation and interleukin-2, interleukin-3, and interferon-gamma release were determined at 2 hrs after trauma-hemorrhage. MEASUREMENTS AND MAIN RESULTS: These immune functional capacities were maintained in proestrus sham-ovariectomized mice after trauma-hemorrhage, whereas they were suppressed in ovariectomized mice subjected to trauma-hemorrhage. 17beta-Estradiol in vitro had no effect on splenocyte functions in proestrus sham-ovariectomized females; however, addition of 17beta-estradiol to splenocytes from ovariectomized females subjected to trauma-hemorrhage normalized immune functional capacities. CONCLUSIONS: These findings suggest that elevated circulating 17beta-estradiol in proestrus females plays a direct role in the maintenance of immunocompetence after trauma-hemorrhage.

Animals↗
PubMed1981

Basal and GnRH-induced release and synthesis of LH and FSH from incubated pituitary glands throughout the 4-day estrous cycle of the rat.

A comparative study of the patterns of LH and FSH released and synthesized during the normal estrous cycle of the rat was performed in vitro. Groups of female rats were killed at 09.00 h and 15.00 h throughout the 4-day estrous cycle and the adenohypophysis incubated for 4 h. Pituitary extracts and media were assayed for LH and FSH by radioimmunoassay. Both hormones exhibited maximum concentrations in tissue and medium on proestrus afternoon. The increased release of LH occurred during the day of proestrus, while that of FSH lasted from the afternoon of proestrus to the morning of estrus. Synthesis of LH exhibited a marked rising phase from the afternoon of diestrus-2 through the morning of estrus. When release and synthesis of LH and FSH were expressed as percentages of hormone concentration at the beginning of the incubation period, the percentages of FSH were greater than those of LH at all stages of the cycle. Addition of synthetic gonadotrophin-releasing hormone (GnRH) to the incubation medium was followed by a dose-dependent increase in release and synthesis of both LH and FSH. Pituitary responsiveness to GnRH reached a peak on the afternoon of proestrus and fell to a minimum during diestrus. Whereas maximum LH responsiveness correlated with the proestrus discharge of the hormone , that of FSH ceased before the basal release of the hormone, which terminates on estrus. The possible role of sex steroid hormones in regulating in vitro secretion of gonadotrophins and pituitary sensitivity to exogenous GnRH is discussed.

Animals↗
PubMed1978

The physiological role of thyrotropin-releasing hormone in the regulation of thyroid-stimulating hormone and prolactin secretion in the rat.

The physiological role of thyrotropin-releasing hormone (TRH) in the regulation of thyrotropin (thyroid-stimulating hormone, TSH) and prolactin (Prl) secretion has been assumed but not proven. Stimulation of their release requires pharmacologic doses of TRH. Lesions of the hypothalamus usually induce an inhibition of TSH secretion and an increase in Prl. To determine whether TRH is essential for TSH and Prl secretion in the rat, 0.1 ml of TRH antiserum (TRH-Ab) or normal rabbit serum was administered to normal, thyroidectomized, cold-exposed, and proestrus rats through indwelling atrial catheter. Serum samples were obtained before and at frequent intervals thereafter. Serum TSH concentrations in normal, thyroidectomized, cold-exposed, and proestrus rats were not depressed in specimens obtained up to 24 h after injection of normal rabbit serum. In contrast, serum TSH was significantly decreased after the administration of TRH-Ab in all normal (basal, 41+/-8 muU/ml [mean+/-SE]; 30 min, 6+/-2; 45 min, 8+/-3; 75 min, 4+/-2); thyroidectomized (basal, 642+/-32 muU/ml; 30 min, 418+/-32; 60 min, 426+/-36; 120 min, 516+/-146); coldstressed (basal, 68+/-19 muU/ml; 30 min, 4+/-3; 180 min, 16+/-8); and proestrus (basal, 11 a.m., 57+/-10 muU/ml; 1 p.m., 20+/-3; 3 p.m., 13+/-4; 5 p.m., 19+/-3) rats. However, 0.1 ml of TRH-Ab had no effect on basal Prl concentrations in normal or thyroidectomized rats and did not prevent the Prl rise in rats exposed to cold (basal, 68+/-7 ng/ml; 15 min, 387+/-121; 30 min, 212+/-132; 60 min, 154+/-114), or the Prl surge observed on the afternoon of proestrus (basal 11 a.m., 23+/-2 ng/ml; 1 p.m., 189+/-55; 3 p.m., 1,490+/-260; 5 p.m., 1,570+/-286). These studies demonstrate that TRH is required for TSH secretion in the normal, cold-exposed and proestrus rat and contributes, at least in part, to TSH secretion in the hypothyroid rat, but is not required for Prl secretion in these states.

Animals↗
PubMed1985

Changes in the pulsatile pattern of luteinizing hormone secretion during the rat estrous cycle.

To ascertain whether changes in the pattern of GnRH release from the hypothalmus occur during the 4-day rat estrous cycle, the pattern of LH release was characterized on each day of the estrous cycle, and the results were interpreted in light of the changes in pituitary responsiveness to GnRH previously described by this laboratory to occur during this time. Blood samples were taken from intact, freely moving rats via venous catheters at 6- to 10-min intervals for 3-4 h. LH pulse height and LH interpulse interval were quantified on each day of the cycle, and the transition on the afternoon of proestrus from tonic LH release to the preovulatory LH surge was detailed. The effects on the pattern of LH release during estrus of small doses of GnRH (0.4 ng) and the continuous infusion of the opioid antagonist naloxone were also examined. Plasma LH concentrations (NIAMDD rat LH-RP-1) were determined with a highly sensitive LH RIA. LH pulses were identified using the PULSAR algorithim. The LH interpulse intervals of 46 +/- 2 min on diestrous-1 day, 49 +/- 4 min on diestrous day 2, and 60 +/- 8 min on proestrus immediately before the LH surge were not significantly different. There were no changes immediately preceding the preovulatory LH surge on the afternoon of proestrus in either the LH interpulse interval or the LH pulse height. Instead, the transition from tonic LH secretion to the preovulatory LH surge was found to occur abruptly. These data suggest that an abrupt increase in GnRH secretion during the afternoon of proestrus initiates the dramatic rise in LH concentrations. The pattern of LH secretion during the day of estrus differed significantly from that on the other days of the cycle in that no LH pulses were observed. However, the administration of small pulses of GnRH elicited physiological elevations in LH release. Furthermore, the continuous infusion of naloxone to estrous rats immediately stimulated a pulsatile pattern of LH secretion, with a LH interpulse of 56 +/- 4 min. These data indicate that the absence of LH pulses during estrus may result from a deficit in GnRH release. Similar modifications in GnRH release during the other days of the cycle were inferred from the observed changes in LH pulse heights. The LH pulse height of 21 +/- 3 ng/ml on diestrous day 2 was significantly less than the LH pulse height of 41 +/- 4 ng/ml on diestrous day 1 or 35 +/- 4 ng/ml on proestrus before the surge.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Effects of hyperprolactinemia on estrous cyclicity, serum luteinizing hormone, prolactin, estradiol, and progesterone concentrations, and catecholamine activity in microdissected brain areas.

The purpose of the present study was to determine the duration of PRL treatment required to suppress estrous cyclicity and preovulatory LH surges and to ascertain whether such treatment affects cyclicity by altering catecholamine activity and/or ovarian steroid secretion. Rats exhibiting 4-day estrous cycles were treated with ovine PRL (oPRL) or vehicle beginning on diestrous day 1 at 0900 h, diestrous day 2 at 2400 h, proestrus at 0600 h, or proestrus at 1200 h. Jugular veins of rats were cannulated to the level of the right atrium on diestrous day 2. Unrestrained rats were bled on proestrus. Preovulatory LH surges and ovulation were completely blocked, and vaginal cytology remained leukocytic on the expected day of proestrus and estrus when oPRL treatment was begun on diestrous day 1. Such treatment elevated progesterone levels beginning on diestrous day 2 and suppressed the preovulatory rise in estradiol observed on proestrous morning and afternoon in control rats. To determine the effect of oPRL on catecholamine activity, alpha-methylparatyrosine was administered to groups of oPRL- or vehicle-treated rats at 0900 or 1500 h on diestrous day 1, diestrous day 2, or proestrus. Animals were killed 0, 45, or 90 min later. Norepinephrine and dopamine concentrations were measured in the median eminence, suprachiasmatic nucleus, medial preoptic nucleus, striatum, ventral aspect of the stria terminalis, and posterior pituitary gland by radioenzymatic assay. Controls exhibited increased norepinephrine turnover rates in the median eminence, suprachiasmatic nucleus, and medial preoptic nucleus on proestrous afternoon concomitant with preovulatory LH surges. In contrast, oPRL-treated rats showed no such increase. In addition, median eminence dopamine turnover rates were elevated beginning on the afternoon of diestrous day 1 in oPRL-treated rats compared to control values. No other differences in norepinephrine and dopamine turnover rates were observed in oPRL-treated rats compared with controls in any other brain area on any day examined. Thus, the data indicate that elevated PRL concentrations have profound effects on reproductive cyclicity by disrupting ovarian steroid secretion and essential preovulatory neurochemical events in selected brain areas involved in the regulation of LHRH.

Animals↗
PubMed1993

RU486 administration blocks neuropeptide Y potentiation of luteinizing hormone (LH)-releasing hormone-induced LH surges in proestrous rats.

We previously demonstrated that NPY potentiates LHRH-induced LH secretion specifically under endocrine conditions in which preovulatory LH surges are generated. The present study was designed to test the hypothesis that NPY's facilitatory actions are dependent upon preovulatory progesterone secretion. In Exp 1, female rats were fitted with atrial catheters on diestrus. On proestrus, hourly blood samples were collected from 1100-2100 h. At 1230 h, rats received a sc injection of the progesterone receptor antagonist RU486 (6 mg/kg BW) or oil. At 1330 h, rats received pentobarbital (40 mg/kg BW), to block hypothalamic LHRH release, or saline. Every 30 min from 1400-1800 h, pentobarbital-treated rats received iv pulses of LHRH (15 ng/pulse) or saline along with concurrent pulses of NPY (5 micrograms/pulse), or saline. In Exp 2, rats received jugular catheters on diestrus, but were sampled every hour throughout the morning (0700-1600 h), rather than the afternoon, of proestrus. In these morning groups, pentobarbital was injected at 0830 h, and peptides (LHRH or combined LHRH and NPY solutions) were administered as pulses at 30-min intervals between 0900-1300 h. Results from Exp 1 were as follows: administration of RU486 to rats given an ip injection of vehicle at 1330 h and pulses of saline from 1400-1800 h completely blocked the endogenous LH surge. In oil-treated pentobarbital-blocked rats, concurrent administration of NPY with LHRH significantly (P < 0.01) potentiated the ability of LHRH to restore LH surges. However, NPY was without any potentiating effects in animals pretreated with RU486 at 1230 h. RU486 also attenuated the ability of LHRH alone to restore LH surges in pentobarbital-blocked rats. In Exp 2, NPY was without effect on LHRH-induced LH secretion during the morning hours of proestrus. Our results demonstrate that 1) NPY facilitates LHRH-induced LH surges on the afternoon of proestrus; 2) presumptive progesterone receptor blockade by RU486 completely prevents NPY's potentiating effects; and 3) NPY is without effect on the morning of proestrus, before the afternoon surge of progesterone. These findings are entirely consistent with the idea that one function of preovulatory progesterone secretion is to up-regulate pituitary sensitivity to the facilitatory actions of NPY. It is hypothesized that these actions of progesterone together with an increase in NPY neurosecretion mediate the acute increase in pituitary sensitivity to LHRH that occurs just before the LH surge.

Animals↗
PubMed1994

Cells that express luteinizing hormone (LH) and follicle-stimulating hormone (FSH) beta-subunit messenger ribonucleic acids during the estrous cycle: the major contributors contain LH beta, FSH beta, and/or growth hormone.

There is a 2-fold increase in the percentage of gonadotropes bearing LH beta or FSH beta mRNAs or antigens as the cells approach proestrus. The purpose of this study was to identify the source of these cells with dual labeling techniques. The first hypothesis was that they stemmed from small monohormonal gonadotropes (containing only LH or FSH) that were driven to transcribe and translate the other gonadotropin. Alternatively, they may stem from other pituitary cell types. We detected the LH beta or FSH beta mRNAs by in situ hybridization (biotinylated oligonucleotide probes were detected by peroxidase-labeled avidin). Second, immunolabeling protocols localized the pituitary hormones. The percentages of cells with LH beta antigens and FSH beta mRNA increased to 81% of the LH beta antigen-bearing cells by the time of peak expression of FSH beta mRNA. Similarly, FSH beta antigen-bearing cells increased their expression of LH beta mRNA to 40% of such cells by the morning of proestrus. During the peak period of expression (the evening of proestrus), LH antigen-bearing cells had increased their expression of LH beta mRNA to 93%. Furthermore, 81% of the same cells expressed FSH beta mRNA. Thus, at least 80% of cells with LH antigens became bihormonal as the cells approached proestrus. This partially supports the first hypothesis for the origin of the new gonadotropes. However, the dual labeling studies also showed that 47% or 60% of cells with GH antigens expressed LH beta or FSH beta mRNAs, respectively, during peak expression (14% of pituitary cells contained gonadotropin mRNAs and GH antigens). Expression by cells with other antigens was low or absent (< 5% of pituitary cells). Perhaps a subset of somatotropes expresses gonadotropin mRNAs. Alternatively, the labeling could signify the presence of GH bound to GH receptors in gonadotropes. In either case, it appears that GH cells may be somehow linked to gonadotrope function as the cells approach proestrus.

Animals↗
PubMed1994

Acute increase in responsiveness of luteinizing hormone (LH)-releasing hormone nerve terminals to neuropeptide-Y stimulation before the preovulatory LH surge.

Neuropeptide-Y (NPY) neurons regulate LH secretion in part through facilitation of LHRH release. We tested the hypothesis that responsiveness of LHRH neurons to NPY's facilitatory actions is physiologically regulated during the estrous cycle, and specifically, that it may be increased as a component of the gonadotropin surge-generating process. A dynamic superfusion paradigm was used to examine the role of cycle stage and time of day on LHRH responsiveness to NPY stimulation, using median eminence tissue from animals killed at 0900, 1400, and 1800 h on metestrus and proestrus. Tissue obtained at 0900 and 1800 h on metestrus did not exhibit significant LHRH responses to 10(-7) M NPY, and only moderate responses were seen at 1400 h on metestrus and 0900 h on proestrus. At 1400 h on proestrus, however, median eminence responsiveness to the same concentration of NPY was significantly increased, with LHRH responses to NPY being 2- to 5-fold greater than those at 0900 (P < 0.01), 1400 (P < 0.05), and 1800 h on metestrus (P < 0.01) and at 0900 h on proestrus (P < 0.05). Neither cycle-related changes in basal LHRH release nor changes in the releasability of LHRH in response to depolarization could account for the accentuated responses in the 1400 h proestrous group. These data clearly demonstrate that the responsiveness of LHRH terminals and/or their afferents to the actions of NPY is acutely enhanced during a brief window of time on proestrus, viz. immediately before generation of gonadotropin surges. Our findings are consistent with the hypothesis that the preovulatory endocrine milieu permits an acute increase in the responsiveness of LHRH nerve terminals to the actions of NPY, perhaps by prompting increases in the number and/or affinity of NPY receptors.

Animals↗
PubMed1975

Changes of hypothalamic LH-RF content during the rat estrous cycle.

Anti-LH-RF serum was produced in rabbits by synthetic LH-RF-BSA conjugate prepard with bis-diazotized benzidine. Employing this antiserum, a radioimmunoassay for LH-RF was established with the assay range from 0.8 to 10 ng/ml. Acid extracts of hypothalami from 4 day cycling rats through various stages of the estrous cycle particularly in the afternoon of proestrus were measured for their LH-RF contents. The hypothalamic LH-RF content was high at 10:00 on the day of proestrus and declined until 17:00 and thereafter, the content gradually increased to reach the basal level. Serum LH showed the highest level at 17:00 on the day of proestrus and fell at 21:00 on the same day. Accompaning this change of serum LH level, pituitary LH content began to decrease at 17:00 of proestrus. These results indicate that LH-RF released in the afternoon of proestrus may participiate to stimulate the preovulatory discharge of LH in the rat.

Animals↗
PubMed2004

Orexin A and B levels in the hypothalamus of female rats: the effects of the estrous cycle and age.

OBJECTIVE: Orexins have been implicated in the regulation of several physiological functions including reproduction, energy balance and vigilance state. For successful reproduction, the precisely timed hormonal secretions of the estrous cycle must be combined with appropriate nutritional and vigilance states. The steroid- and nutritional state-dependent modulation of LH release by orexins, as well as an increase of vigilance, suggest that orexins may co-ordinate these functions in the course of the estrous cycle. DESIGN: We studied the brain tissue levels of orexins in the course of the estrous cycle in young and middle-aged rats. Young cycling rats (3 months old) and irregularly/non-cycling (7-9 months old) female rats were inspected for vaginal smears and serum hormone levels. METHODS: Tissue concentrations of orexin A and B were measured in the hypothalamus and lateral hypothalamus on different days of the estrous cycle. RESULTS: Orexin A concentration in the hypothalamus of young cycling rats was higher on the day of proestrus 5-6 h after the lights were switched on than on the other days of the estrous cycle at the same circadian time. Orexin B concentration was higher on both the day of proestrus and the day of estrus as compared with the days of diestrus. The hypothalamic concentrations of both orexin A and B in the non-cycling middle-aged rats were lower than those in cycling rats on the days of proestrus and estrus. CONCLUSIONS: We have concluded that the high hypothalamic concentration of orexins on the day of proestrus may contribute to the LH and prolactin surges. High orexin A levels may also contribute to the decreased amount of sleep on the day of proestrus.

Aging↗
PubMed1998

Differential expression and selective localization of vascular permeability factor/vascular endothelial growth factor in the rat uterus during the estrous cycle.

This study examines the expression of the multi-functional cytokine, vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) in the rat uterus during early proestrus, proestrus, estrus and diestrus. Groups of ovariectomized or hypophysectomized rats served as endocrine controls. Expression of VPF/VEGF mRNA was 2-fold greater in uteri during proestrus and estrus than in other phases of the estrous cycle. In situ hybridization techniques indicated that VPF/VEGF mRNA expression was confined to the luminal epithelium during proestrus, but shifted to the stromal compartment during estrus. Ovariectomized, hypophysectomized or diestrus rats exhibited scattered localization of VPF/VEGF mRNA among glandular epithelium and endometrial stromal compartments. Although VPF/VEGF mRNA was expressed throughout the estrous cycle, but in different compartments of the endometrium depending on the stage of the estrous cycle, VPF/VEGF protein expression appears to be restricted to the epithelial compartment during proestrus and estrus. Results indicate that circulating levels of gonadal steroids and LH may be associated with the differential expression of VPF/VEGF mRNA and its translation activity in the endometrium during different stages of the estrous cycle.

Animals↗
PubMed1988

Induction of estrus in greyhound bitches with prolonged idiopathic anestrus or with suppression of estrus after testosterone administration.

Twelve anestrous adult Greyhound bitches were used to study a regimen for induction of estrus. Once daily, 7 bitches were given diethylstilbestrol (DES; 5 mg, PO) until sanguineous vaginal discharge and vulvar edema were observed (designated as day 1 of proestrus) and for 2 days thereafter. If no response was elicited after 7 days, a doubled DES dose was given for up to an additional 7 days. Luteinizing hormone (5 mg, IM) was given on day 5 of proestrus, and follicle-stimulating hormone (10 mg, IM) was given on days 9 and 11 of proestrus. Bitches were bred once on day 13. Five bitches were used as a control group; they were given candy tablets for 7 days (first day on tablets, treatment day 1) and 0.9% NaCl (1.0 ml, IM) on treatment days 12, 16, and 18. The 7 bitches treated with DES had a mean proestrus period of 7.7 days and a mean estrus period of 5.7 days up to the day of mating. After mating, they had a mean gestation interval of 64 days and delivered a mean of 4 pups/litter. In 5 bitches, initial treatment with 5 mg of DES/day induced proestrus within 7 days; however, in 2 bitches, additional treatment with 10 mg of DES/day was needed for 5 and 6 days, respectively. Serum estradiol-17 beta and progesterone concentrations remained at base line during the period of DES treatment. Concentrations of both hormones increased after injection with luteinizing hormone and remained high for the next 4 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Anestrus↗
PubMed1976

Importance of mammary gland DNA synthesis on carcinogen-induced mammary tumorigenesis in rats.

DNA synthesis in mammary gland estimated by [3H]thymidine incorporation was significantly higher on the day of proestrus than on the second day of diestrus in 50-day-old female Sprague-Dawley rats. The percentage of progressive mammary tumors, tumor growth rate, and the number and the weight of tumors per tumor-bearing rat were significantly higher in the animals given a single i.v. injection of 5 mg 7,12-dimethylbenz(a)anthracene at proestrus than in the animals given it at diestrus. Inhibition of DNA synthesis at proestrus by 2-bromo-alpha-ergocryptine also suppressed mammary tumorigenesis by the carcinogen. In 90-day-old rats in which little difference was found in mammary gland DNA synthesis between proestrus and diestrus, there was no difference in mammary tumorigenesis between animals given the carcinogen at proestrus and animals given it at diestrus. On the other hand, the prestimulation of mammary gland DNA synthesis by prolactin increased the growth, the number, and the weight of carcinogen-induced mammary tumors. These results demonstrate the importance of mammary DNA synthesis at the time when a carcinogen acts on the glands in mammary tumorigenesis.

Age Factors↗
PubMed1981

Cellular junctions in perifollicular contractile tissue of the rat ovary during the preovulatory period.

Rat ovarian perifollicular contractile tissue was examined at specified intervals prior to ovulation to determine the type, relative number, and length of cellular junctions. Rat ovaries were taken for electron-microscopic observation at 1500 h on the afternoon of proestrus (proestrus 0-h group), at 2000 h (proestrus 5 h group), at 0100 h (proestrus 10-h group) and at 1600 h on the afternoon of diestrus I. Close junctions, intermediate junctions, and gap junctions were counted and measured. Then number of gap junctions/1,000 micrometers of membrane and the number of intermediate junctions/1,000 micrometers of membrane was significantly higher in the proestrus 10 h groups as compared to the other groups. There was no difference in the number of close junctions during the periods studied. Also the length of all junctions was similar in all groups. These morphological findings are discussed in the context of contractile role for perifollicular tissue in the ovulatory process.

Animals↗