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PubMed1985

Mounting behavior as affected by stage of estrous cycle in Holstein heifers.

Nine Holstein heifers whose estrous cycles were synchronized were observed during three subsequent consecutive cycles. Observations of heifers during each periestrus period began when the first heifer reached day 15 of an estrous cycle and ended 36 h after onset of estrus for the ninth heifer. There were 118 1-h observations at 6-h intervals during the three periestrus periods. Estrous cycles were divided into postestrual, luteal, preestrual, and estrual stages by blood progesterone profiles and estrus. Heifers of these four stages accounted for 27.5, 48.3, 15.4, and 8.8% of heifers available to mount during the 118 observations, and heifers of each stage made 9.0, 5.2, 18.9, and 66.9% of attempted mounts. When number of heifers in estrus simultaneously increased from one to five, total attempted mounts and stands per hour increased from 10.1 to 63.5 and from 4.5 to 48.5. Stands per heifer per hour increased significantly as number of heifers in estrus increased from one to two and tended to increase as number in estrus increased further. Presence of one preestrual heifer in a group containing one estrual heifer increased total stands per hour from 2.3 to 5.0. Efficiency of detection of estrus may depend on proportion of animals within estrous cycle stages that have highest mounting activity.

Animals↗
PubMed1983

A quantitative immunocytochemical study of the luteinizing hormone and follicle-stimulating hormone cells in the adenohypophysis of adult male rats and adult female rats throughout the estrous cycle.

We investigated whether 1) the absolute or the relative numbers of LH and FSH cells change during the rat estrous cycle, 2) the percentages of gonadotrophs that contain LH and/or FSH change during the estrous cycle, and 3) gonadotrophs change in size during the rat estrous cycle. Groups of four female rats were decapitated at one of five different times during the estrous cycle. Four male rats were also decapitated. Serum concentrations of LH and FSH were determined by RIA. Paired horizontal flip-flopped or nonflipped paraffin sections were mounted from the dorsal, middle, and ventral portions of each pituitary gland. In each pair of sections, one was stained with a-rat LH-S4 and the other with a-rat FSH-S7 by the unlabeled antibody peroxidase-antiperoxidase method. All immunoreactive cells were counted. Photographs were taken from randomly chosen corresponding areas, and the cells were individually matched to determine the percentage that contained one or both hormones. Correction factors had to be used because in paired flip-flopped or nonflipped sections stained with the same antibody (a-rat LH-S4), not all of the stained cells found in one section were found in the other section. The absolute numbers of LH and FSH cells did not change throughout the estrous cycle. The ratio of LH cells to FSH cells in the pars distalis of female rats was also constant throughout the estrous cycle. In female rats, 75.2% of LH cells also contained FSH, while 99.4% of FSH cells also contained LH. In the male rats, 88.6% of LH cells also contained FSH, while 98.6% of FSH cells also contained LH. Similar results were obtained in paired flip-flopped sections stained with a-rat LH beta and a-rat FSH beta. Sequential staining of additional individual tissue sections with a-rat LH-S4 and then a-rat FHS-S7 or vice versa revealed the following. Staining of LH-stained tissue for FSH revealed less than 1% new cells, but staining of FSH-stained tissue for LH revealed a 8.7% increase in gonadotrophs in males and a 25.4% increase in females. The gonadotrophs in female rats did not change in size during the estrous cycle and were significantly smaller than the gonadotrophs in male rats. The results suggest that in normal adult rats: 1) virtually all FSH-containing cells contain LH, 2) about 25% of the gonadotrophs in females and about 11% of the gonadotrophs in males contain LH but not FSH, 3) the number of cells containing LH or those containing LH and FSH does not change during the estrous cycle, 4) gonadotrophs in female rats do not change in size during the estrous cycle and are smaller than the gonadotrophs in male rats, and 5) FSH release during the early morning of estrus, when the serum FSH concentration is elevated and the serum LH concentration is low, occurs from cells that contain both LH and FSH.

Animals↗
PubMedDate not supplied

[Dependence of the reversal training of rats in a Y-maze and their haloperidol sensitivity on the estrous cycle phase].

In female rats estrous cycle related variations were found in reversal learning in a Y-maze. Low intersession fluctuations of errors and a high number of well relearning rats were obtained on the day of diestrus I as compared with estrus. The improvement of avoidance behaviour by haloperidol (0.1 mg/kg) also was better in diestrus I. The estrous cycle dependent variations of the behavior and neuroleptic effect may be a result of periodicity of ovarial hormones secretion and their influences on the brain dopaminergic systems.

Animals↗
PubMed1998

Progesterone concentrations during estrous cycle of dairy cows exposed to electric and magnetic fields.

Sixteen multiparous nonpregnant lactating Holstein cows (each weighing 662 +/- 65 kg in 150.4 +/- 40 day of lactation) were confined to wooden metabolic cages with 12:12 h light:dark cycle during the experiment. The cows were divided into two sequences of eight cows each and exposed to electric and magnetic fields (EMF) in an exposure chamber. This chamber produced a vertical electric field of 10 kV/m and a uniform horizontal magnetic field of 30 microT at 60 Hz. One sequence was exposed for three estrous cycles of 24 to 27 days. During the first estrous cycle, the electric and magnetic fields were off; during the second estrous cycle, they were on; and during the third estrous cycle, they were off. The second sequence was also exposed for three 24 to 26 days estrous cycles, but the exposure to the fields was reversed (first estrous cycle, on; second estrous cycle, off; third estrous cycle, on). The length of each exposure period (21 to 27 days) varied according to the estrous cycle length. No differences were detected in plasma progesterone concentrations and area under the progesterone curve during estrous cycles between EMF nonexposed and exposed periods (2.28 +/- 0.17 and 2.25 +/- 0.17; and 24.5 +/- 1.9 vs. 26.4 +/- 1.9 ng/ml, respectively). However, estrous cycle length, determined by the presence of a functional corpus luteum detected by concentrations of progesterone equal to or more than 1 ng/ml plasma, was shorter in nonexposed cows than when they were exposed to EMF (22.0 +/- 0.9 vs. 25.3 +/- 1.4 days).

Animals↗
PubMed1994

Caudal brain stem plays a role in metabolic control of estrous cycles in Syrian hamsters.

In Syrian hamsters, a critical factor necessary for the occurrence of normal estrous cycles appears to be the cellular availability of oxidizable glucose. For example, estrous cycles are inhibited by food deprivation or treatment with 2-deoxy-D-glucose (2DG), a drug that inhibits cellular glucose utilization. Several lines of evidence suggest that these effects require the participation of neurons in part of the caudal brain stem, the area postrema (AP) and adjacent, reciprocally-innervated nucleus of the solitary tract (NTS). This study was designed to examine the role of the AP in 2DG-induced anestrus. Hamsters received either aspiration lesions directed at the AP or sham operations. Between 12 and 16 days after surgery, both sham-operated and lesioned hamsters showed two consecutive 4-day estrous cycles, as measured by estrous behavior and vaginal discharge. Subsequently, both groups were treated with doses of 2DG known to inhibit the estrous cycle (1750 mg/kg every 6 h on days 1 and 2 of the cycle). Hamsters were tested for measures of estrous cyclicity daily after treatment. Only 9% of the sham-operated hamsters showed estrous cycles within 5 days after the start of 2DG treatment. In contrast, all of the hamsters with confirmed lesions of the AP showed estrous cycles within 5 days of the start of 2DG treatment. Histology showed that most lesions removed the AP plus part of the medial NTS, while two lesions removed part of the AP only.(ABSTRACT TRUNCATED AT 250 WORDS)

Anestrus↗
PubMed1982

Alteration of the estrous cycle of gilts by movement to a confinement housing system.

Thirty-six crossbred gilts were maintained in outside dirt lots for 2 or more estrous periods. Eighteen of the gilts were moved to another outside dirt lot (non-confined) and the other eighteen were moved to a single pen in a confinement finishing building (confined). A blood sample was collected on the day of movement and every 7 days thereafter for 12 weeks and quantitated for progesterone to verify the occurrence of each ovulation. Any estrous cycle shorter than 18 days or longer than 23 days was classified as abnormal. The duration of estrous cycles of non-confined gilts were not different before, during or after movement, whereas the duration of estrous cycles were greater (P=.005) during movement than before movement in the confined gilts. The duration of estrous cycles of confined gilts were greater (P=.020) than those of non-confined gilts during movement. The percentage of abnormal estrous cycles were greater during movement than before (P=.007) or after (P=.052) movement for the confined gilts, whereas the percentage age of abnormal estrous cycles were greater (P=.050) during movement than before movement in non-confined gilts. Therefore, the greatest percentage of abnormal estrous cycles occurred during movement in both groups. A single incident of silent estrus followed by normal estrous cycles was observed. In addition, an estrus occurred while plasma progesterone concentration was elevated (51 ng/ml) and was followed by normal estrous cycles.

Journal Article↗
PubMed2006

Analysis of endometrial myeloid and lymphoid dendritic cells during mouse estrous cycle.

This study was performed to evaluate the frequency and localization of endometrial myeloid (CD11c(+) CD11b(+)) and lymphoid (CD11c(+) CD8alpha(+)) dendritic cells (DCs) at different stages of murine estrous cycle. To address the systemic effect of ovarian hormones fluctuations during estrous cycle, the same variables were studied in splenic DCs as well. Stages of the estrous cycle of Balb/c mice were determined by examination of vaginal smears. Frozen sections of uterus and spleen at each stage of estrous cycle were stained for CD11c and MHC-II. Two-color immunohistochemistry was also carried out using anti-CD11c with one of the antibodies against CD11b, CD8alpha, CD86, and DEC-205. The average density of DCs and relative percentage of myeloid and lymphoid DCs (MDCs and LDCs) were determined at each stage of estrous cycle by morphometric analysis. Our results showed that DCs were present throughout the estrous cycle in mice endometrium, but their frequency was highest at estrus and lowest at proestrus (P<0.005). The lymphoid subset of DCs was more prominent at estrus relative to those at other stages (P<0.005). Conversely, the relative percentage of myeloid DCs at estrus was significantly lower compared to other stages (P<0.005). Nearly all endometrial and splenic DCs expressed CD86 and MHC-II. At proestrus, and particularly at estrus, DCs were more concentrated subadjacent to the luminal and glandular epithelial layers with some scattered throughout the stroma whereas, at metestrus and diestrus, DCs were randomly distributed in stroma and around the glandular and luminal epithelial layers. The number and immunophenotype of splenic DCs were not statistically different between stages of estrous cycle. Our results suggest that endometrial but not splenic myeloid and lymphoid DCs are influenced by steroid hormones during estrous cycle.

Animals↗
PubMed1997

Effects of the estrous cycle and the gender differences on hepatic drug-metabolising enzyme activities.

The aim of the present study was to investigate the effects of the estrous cycle and physiological dose of estradiol (E2) and the gender difference on several hepatic drug-metabolising enzyme activities. Eight-week old female Sprague-Dawley rats at different stages of the estrous cycle [proestrous (P), estrous (E), and diestrous (D)] and 8-week old male rats were used in this study (n = 5, respectively). Serum E2 level at D was higher than that at E and lower than that at P. The hepatic cytochrome P450 content, aniline hydroxylase, ethoxycoumarin O-deethylase and aminopyrine N-demethylase activities in male were significantly higher than those in female at any stage of the estrous cycle and these activities in female remained unchanged during the estrous cycle. Neither the estrous cycle nor the gender difference affected the cytochrome b5 content. NADPH-cytochrome c reductase (fPT) activity at P was similar to that in male, and was significantly higher than that in E and D. fPT activity was increased by the administration of physiological dose of E2 in ovariectomized rats. Uridine diphosphate glucuronyltransferase (UDP-GT) activity at E was significantly lower than that at P or D and that activity in female was significantly lower than that in male. These results indicate that the estrous cycle, especially serum E2 level, may affect both fPT and UDP-GT activities.

Animals↗
PubMed1980

Accuracy of predicting stages of bovine estrous cycle by gross appearance of the corpus luteum.

Four readily identifiable changes in appearance of corpora lutea (Stages I to IV) occur during a bovine estrous cycle. Accuracy of estimating the stage of an estrous cycle by appearance of corpora lutea was determined in a double-blind study. One investigator observed estrus in a group of heifers while another with no prior knowledge of reproductive histories of the heifers estimated stage of the estrous cycle by visual inspection of their corpora lutea. Stage of the estrous cycle (Stage I, days 1 to 4; Stage II, days 5 to 10; Stage III, days 11 to 17; Stage IV, days 18 to 20) was estimated correctly in 41 of 48 heifers. The correlation between estimated and actual days of the estrous cycle was .81. In addition, concentrations of progestins and weights of corpora lutea during estimated stages of the estrous cycle were similar to many other investigations. Stages of the estrous cycle in heifers can be estimated from appearance of corpora lutea.

Animals↗
PubMedDate not supplied

[A mathematical model of the physiological estrous cycle in outbred rats].

The mathematical model of the physiological estrous cycle of the laboratory rat was developed. The data on physiological concentration of the hormones, participating in the estrous cycle regulation and admittances on the growth and selection of the ovarian follicles made the base of the model. The developed system of differentiated equations allowed to reproduce quiet precisely the duration of the estrous cycle phases, to follow up the behaviour of the apparent cohort of the growing ovarian follicles during several cycles. The model is a base for the studying of the effect of the different factors on the estrous cycle.

Animals↗
PubMed2000

Waves of follicle development during the estrous cycle in sheep.

The pattern of ovarian follicle development in maiden cyclic lambs was characterized using the definition of a follicle wave as the changes in the number of follicles among the days of the estrous cycle, as originally defined in cattle by Rajakoski in 1960. We also examined the steroid content relationships among follicles on Days 5 (Wave 1) and 14 (Waves 2 and 3) of the estrous cycle. In Experiment 1, the ovaries of 20 cyclic lambs (40 to 45 kg) were examined daily using transrectal ultrasonography for 1 or 2 estrous cycles (n = 31 cycles). The number of small (2 and 3 mm in diameter), medium (4 and 5 mm) and large (> or = 6 mm) follicles were aligned with the beginning and end of the average length estrous cycle and then compared among days. Identified follicles were defined as those that grew to > or = 4 mm and remained at > or = 3 mm for > or = 3 d. The number of identified follicles emerging (retrospectively identified at 2 or 3 mm) per ewe per day was also aligned with the average length estrous cycle. In Experiment 2, ewe lambs were ovariectomized on Day 5 (n = 6) or 14 (n = 5) of the estrous cycle, then follicle diameters and follicular fluid concentrations of estradiol and progesterone were compared among follicles. Data were analyzed by repeated measures ANOVA and compared among days using Fisher's LSD. In Experiment 1, either 2 (n = 10 cycles), 3 (n = 20 cycles) or 4 (n = 1 cycle) periods of emergence of identified follicles occurred during individual cycles, with estrous cycle lengths of 15.6 +/- 1.6, 16.1 +/- 1.1 and 17 d respectively. In animals with 2 or 3 periods of emergence of identified follicles, the total number of small, medium and large follicles differed (P < 0.05) among days of the estrous cycle showing a wave-like pattern. In Experiment 2, a single follicle collected on each of Days 5 and 14 of the cycle (6.2 +/- 0.2 and 3.9 +/- 0.2 mm in diameter) had a higher (P < 0.05) concentration of follicular fluid estradiol (36.2 +/- 4.4 and 50.9 +/- 21.6 ng/mL) than other follicles collected on the same day (next largest follicle: 4.3 +/- 0.3 and 3.5 +/- 0.4 mm; 4.3 +/- 0.9 and 18.2 +/- 6.7 ng/mL estradiol). The results showed that 1) there was a synchronous emergence of follicles associated with fluctuations in the number and size of follicles during the estrous cycle; 2) within a wave there was a hierarchy among follicles for diameter and steroid content; 3) ovarian follicle growth in ewe lambs occurred in 2 or 3 organized waves during the estrous cycle.

Animals↗
PubMed1995

Protein tyrosine kinase expression during the estrous cycle and carcinogenesis of the mammary gland.

The susceptibility of the mammary epithelium to neoplastic transformation is linked to the exposure to estrogen during the estrous cycle. The effects of the estrous cycle on the mouse mammary gland have been investigated by analyzing 3H-thymidine incorporation, milk protein gene expression and DNA fragmentation. We found that the mammary epithelium undergoes limited proliferation, differentiation and apoptosis in a cycle-dependent manner. The estrous-responsive regulators of the mammary epithelium are unknown; however, considering the integral role of protein tyrosine kinases (PTKs) in the control of normal and malignant development, members of this family of enzymes are likely candidates for such regulatory molecules. Using a RT-PCR-based cloning strategy, we have undertaken a survey of PTKs expressed in the mammary gland at defined stages of development, with special emphasis on the estrous cycle. We identified 21 known and 4 novel PTKs. Their expression was analyzed throughout mammary gland development and in mammary neoplasias using a transgenic mouse model for invasive and non-invasive carcinogenesis. Most of the identified PTKs showed highest expression during the estrous cycle and were down-regulated during pregnancy and lactation. Deregulated expression was rarely observed in the non-invasive mammary tumors. In contrast, 10 of 19 PTKs expressed during the estrous cycle were also over-expressed in the invasive carcinomas, mostly involving members of the receptor family of PTKs.

Amino Acid Sequence↗
PubMed1988

Dynamic change in charge heterogeneity of pituitary FSH throughout the estrous cycle in female rats.

Anterior pituitaries were removed from female rats at various stages during the estrous cycle and FSH was fractionated by isoelectric focusing (IEF). Fourteen FSH components were observed during the estrous cycle and twelve of them were distributed between pH 3.71 and 6.66. IEF profiles of FSH in the pituitaries varied with the stage in the estrous cycle. Especially at the time of serum FSH surge on the day of proestrus, most of the components decreased, while only a highly alkaline component showed an increase. When these FSH components were separated and their nature was examined by radioreceptor assay (RRA), radioimmunoassay (RIA) and gel filtration, differences were observed among these components in the RRA/RIA ratio and gel filtration profile. As a general tendency, the RRA/RIA ratio of the components became greater while the apparent molecular size became smaller, as their pI became higher. However, some highly acidic components showed a biphasic elution pattern and the most acidic one eluted the latest on gel filtration, suggesting that these components may be heterogeneous in terms of molecular size. The FSH concentration in sera collected at different stages in the estrous cycle was measured by both RRA and RIA. The RRA/RIA ratio was high when the serum immunoreactive FSH was low, and low during the FSH surge. From these findings, it is concluded that the quality of FSH molecules present in the anterior pituitary gland changes dynamically throughout the estrous cycle, especially during the period of serum FSH surge. Furthermore it is suggested that the type of FSH secreted from it also varies according to the stage in the estrous cycle.

Animals↗
PubMed1996

Nonluteal estrous cycles of 3-week duration are initiated by anovulatory luteinizing hormone peaks in African elephants.

Previous attempts to characterize the estrous cycle of elephants have yielded conflicting estimates of cycle length and LH profiles. In order to establish artificial breeding programs in this species, resolution of these issues is needed. Therefore, four female African elephants housed at the Indianapolis Zoo were studied for approximately 6 mo beginning in December 1994. Blood was collected weekly, and the serum was immediately analyzed for progesterone (P4). Whenever the weekly concentration of P4 was found to be low, blood was collected one or four times per day. All serum samples were assayed for LH, and the daily samples were assayed for P4 and estradiol. Transient increases of serum LH (designated as peaks) were observed four times in each of the four females. Of these 16 LH peaks, 8 were classified as ovulatory LH (ovLH) peaks and 8 were classified as anovulatory LH (anLH) peaks. Peaks designated ovLH averaged 3.60 +/- 0.67 ng/ml (mean +/- SEM); serum P4 measured during these peaks began to increase 2-3 days before each ovLH peak and continued to increase for several weeks thereafter, reaching a peak of 675 +/- 35 pg/ml. The eight other LH peaks, designated anLH peaks, were of similar (p > 0.05) magnitude averaging 3.07 +/- 0.72 ng/ml, but the serum concentration of P4 remained very low (< 80 pg/ml) during and for several weeks after these peaks. Six peaks designated anLH occurred an average of 12.2 +/- 1.4 days after serum P4 had declined below 80 pg/ml. In each elephant, there was a regular sequence in which each ovLH peak was followed by a luteal-active period lasting about 60 days and then about 12 days later by one anLH peak. Each anLH peak was followed 19-22 days later by one ovLH peak, but serum P4 remained at nonluteal levels throughout this interval between peaks. The authors propose to designate this interval after the anLH peak and before the next ovLH peak as a nonluteal (i.e., low P4) estrous cycle of only 3-wk duration. Following each short nonluteal estrous cycle, there was a single ovLH peak that initiated one luteal-active estrous cycle lasting 10-11 wk until terminated by the next anLH peak. The present results demonstrate that nonpregnant African elephants, housed in the absence of males, alternate between short nonluteal estrous cycles and long luteal-active estrous cycles. Daily measurements of serum P4 can be used to distinguish between the two types of estrous cycles and thereby provide a clinical prediction about the optimum time for artificial insemination.

Animals↗
PubMed1987

Transient shortening of estrous cycles in aging C57BL/6J mice: effects of spontaneous pseudopregnancy, progesterone, L-dihydroxyphenylalanine, and hydergine.

Regular estrous cycles can be reinitiated in old acyclic female rats by pharmacologic, hormonal, and environmental manipulations. The most responsive acyclic states are persistent vaginal cornification (PVC) and spontaneous pseudopregnancy (SP). However, it is not known if the irregular cyclicity that precedes acyclicity during aging can also be alleviated. We found that transient shortening of estrous cycles follows smear sequences indicative of pseudopregnancy in C57BL/6J mice, aged 9-15 mo, suggesting a role for progesterone. This phenomenon was investigated through a limited model of pseudopregnancy in which intact aging mice with lengthened cycles were given progesterone implants (yielding 70 ng progesterone/ml plasma) that suppressed estrous cycles; upon removal of the implants, cycles were transiently shortened in aging mice. Therefore, we hypothesize that withdrawal from the progesterone elevations associated with SP is the mechanism in shortening subsequent estrous cycles. Effects of central-acting drugs, similar to those used to reinitiate cyclicity in acyclic old rats, were also examined. Hydergine, an ergot mixture with partial dopaminergic and serotonergic agonist activities, suppressed SP when fed to 10- to 12-mo-old, middle-aged mice. Hydergine did not otherwise affect estrous cycle length, prevent PVC, or reinitiate cycling in acyclic PVC mice. Feeding L-dihydroxyphenylalanine to middle-aged mice did not suppress SP, affect estrous cycle lengths, or reinitiate cycles from PVC.

Aging↗
PubMedDate not supplied

Level of energy intake affects the estrous cycle in Sundevall's jird (Meriones crassus).

Effects of energy intake on the estrous cycle of the desert gerbillid, Sundevall's jird (Meriones crassus; 80 g; n=22) were studied. Females were offered either maintenance or below maintenance levels of millet seeds and ad lib. Atriplex halimus leaves and stems; drinking water was not available. Vaginal smears were used to determine sexual stage. We hypothesized that the estrous cycle ceases at low levels of energy intake and commences when sufficient energy is available. Females lost body mass linearly with a decrease in metabolizable energy intake. Estrous cycle averaged 4.46 d at maintenance energy intake but increased to an average of 7.81 d at 70% of maintenance energy intake. A cessation of the cycle occurred at an energy intake below 70% of maintenance requirements, which resulted in a body mass loss of more than 1% per day. More variability in the length of the different stages of the cycle was found with lower levels of energy intake. When offered ad lib. millet seeds and A. halimus (n=14), recovery to the normal cycle was attained within 10 d by 43% of the females and within 16 d by the rest of the females. Recovery time was longest in females that previously had the lowest energy intake. We concluded that the estrous cycle of M. crassus is sensitive to energy intake. With restricted energy intake, the estrous cycle and reproductive activities cease but can be restored with provision of adequate energy. This strategy ensures that reproduction occurs when conditions of food availability and body condition of the females are favorable.

Animals↗
PubMed2006

[Influences of orthodontic tooth movement on estrous cycle and estrogen in rats].

OBJECTIVE: To explore the influences of orthodontic tooth movement on estrous cycle and estrogen in female rats. METHODS: Two hundred female rats were divided into control group, one-time activation group, four-time activation group and sham-operated group. Each group was divided again into 4 sub-groups according to the different stage of the estrous cycle. The force-loading groups received repeated intermittent force. Serum estrogen was measured and the change of estrous cycle was recorded. RESULTS: There were significant variations in the estrogen level among the groups which received mechanical force during the same stage of the estrous cycle (P < 0.01) and among the subgroups within each group (P < 0.05). These experimental treatments affected the estrous cycle of the rats in the groups received force in metestrus and diestrus. CONCLUSIONS: Estrus of rats was the appropriate time for the orthodontic force.

Animals↗
PubMed1982

The contribution of gonadostatin (inhibin-F) to the control of gonadotropin secretion in a simulated estrous cycle in steroid-treated ovariectomized rats.

We have examined the contribution of gonadostatin to the control of gonadotropin secretion throughout the rat estrous cycle. The estrous cycle was simulated in rats ovariectomized on diestrus-1, designated day 1 (D-1) by use of low or high level estradiol and progesterone Silastic implants. The steroid implant regimen simulated the major changes of these hormones in the blood during the course of the estrous cycle. Injections of porcine follicular fluid (pFF) were superimposed on this steroid regimen. Four treatment combinations of steroid and pFF or their controls were tested: 1) steroid implants only, 2) pFF only at a constant dose level, 3) steroid implants and pFF injections at a constant dose level, and 4) steroid implants and pFF injections with reduced levels on simulated proestrus. In group 1 both basal and surge release of LH were similar to those in the intact rat, but both basal and surge release of FSH were significantly elevated above levels observed in the intact rat for the respective periods. In group 2 FSH was suppressed to diestrous levels throughout the course of the experiment, with no surge occurring on D-3. Serum LH levels were slightly elevated above diestrous levels (50-150 ng/ml) with no surge. In group 3 serum levels of both gonadotropins were suppressed to diestrous levels on D-1 and D-2, and a steroid-induced, pFF-attenuated surge occurred on the afternoon of D-3. Group 4 had, with a minor variation, proestrous-like FSH and LH surges on D-3 and basal (diestrous) gonadotropin levels during simulated D-1, D-2, and early proestrus. This study supports previous evidence for estradiol and progesterone control of LH secretion and elaborates the control of FSH secretion. The role of gonadostatin and steroids is demonstrated in the negative feedback regulation of FSH secretion.

Animals↗