Oestrogen and progesterone content of ovarian vein blood of the ewe during the oestrous cycle

Cell-specific expression of estrogen-responsive genes in the uteri of cyclic, early pregnant and ovariectomized ewes

A single physiological dose of estradiol up-regulates estrogen receptor-alpha(ER), progesterone receptor (PR), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), c-fos, cyclophilin, and actin mRNAs in the endometrium of ovariectomized ewes. Therefore, we hypothesized that these genes would be up-regulated by the preovulatory surge of estrogen which occurs on the evening of Day 15 in the estrous cycle of sheep. ER and PR mRNA concentrations increased between Day 15 and Day 1 in cyclic ewes in most endometrial epithelial cells, while GAPDH mRNA increased in epithelial and stromal cells in the deep endometrium. Day 15 pregnant ewes had lower expression of ER, PR, GAPDH, cyclophilin and actin genes. For ER and GAPDH mRNAs, the greatest reduction occurred in the superficial endometrium. Ovariectomized ewes demonstrated concentrations of ER, PR, and GAPDH mRNAs that were similar to those in the cyclic ewes. While concentrations of c-fos mRNA did not differ between groups, those of cyclophilin and actin mRNAs were lower in the pregnant and ovariectomized ewes. In conclusion, ER, PR and GAPDH gene expression rose during estrus in endometrial cells with the highest ER gene expression and were repressed in pregnant ewes in superficial endometrial cells with the greatest PR gene expression.

Changes in preoptic and hypothalamic levels of progesterone receptor mRNA across the oestrous cycle of the ewe

We measured the levels of progesterone receptor (PR) mRNA in the hypothalamus and preoptic area (POA) of the ewe across the oestrous cycle. Perfusion-fixed hypothalamic tissue was collected from sheep killed during the luteal and follicular phases and during behavioural oestrus. Blood samples taken at the time of tissue collection verified that the oestrous ewes were undergoing a preovulatory luteinizing hormone (LH) surge. Matched sections were taken from the POA, periventricular nucleus (PeVN), ventromedial nucleus (VMN) and arcuate nucleus of each animal. In situ hybridization was performed using a sheep specific, (35)S-labelled riboprobe for PR and semiquantitative image analysis was conducted on emulsion-dipped slides. The number of silver grains per cell was greater in the VMN and arcuate nucleus of oestrous ewes than in luteal and follicular phase ewes; there was no cyclic variation in the level of PR mRNA expression in the cells of the POA and PeVN. The number of labelled cells per mm2 in the VMN was higher in the oestrous ewes than in luteal phase and follicular phase ewes. The number of labelled cells in the PeVN was also higher in the oestrous ewes than in follicular phase ewes, but there was no cyclic variation in the POA and arcuate nucleus. In the ewe, the onset of behavioural oestrus corresponds to the onset of the preovulatory LH surge and increased PR mRNA expression at this time is likely to be due to the high concentrations of circulating oestrogen that precede this period.

LHRH — Induced ovulation and fertility of anestrous goats

Seventeen female mature anestrous does were used to study the effect of luteinizing hormone-releasing hormone (LHRH) on ovulation (Experiment I) and on fertility rate and blood estrogen/progesterone concentrations (Experiment II). Laparotomy after day 8 of treatment with a single injection of LHRH (300 ug) and estradiol cypionate (0.2 mg/kg) revealed evidence of ovulation in two out of three and a developed follicle in the third. Similar treatment to six does in Experiment II, when followed by natural mating with a fertile buck, produced pregnancy in two does, pseudopregnancy in two and no effect (nonpregnancy) in the remaining two animals. The pregnant does had normal parturition after 148 to 150 days of gestation. In pregnant does, blood progesterone levels first showed a gradual increase until day 130 (10.07 ng/ml) and then declined sharply at 48 hours before parturition. Estrogen concentration, on the other hand, failed to increase until day 80, and thereafter it reached a peak (1800 pg/ml) at 24 hours prior to parturition; the level declined sharply at 24 hours after parturition. In pseudopregnant does, progesterone levels remained in close proximity with those of pregnant does until day 90, when they started to decline.

Differential sensitivity of estrogen target tissues: implications for estrogen regulation of serum luteinizing hormone

In the rat, it is generally accepted that the primary site of estrogen's stimulatory (positive) effects on serum LH is the preoptic area-anterior hypothalamus (POA/AH). In contrast, the primary site of estrogen's inhibitory (negative) effects on serum LH levels has not been conclusively identified. There is evidence to suggest both a medial basal hypothalamic (MBH) and an anterior pituitary site of action. The present studies utilized a unique characteristic of these estrogen effects to investigate their putative loci. Extensive dose-response curves of estrogen's induction of positive and negative feedback indicated that the negative feedback response was activated at a lower concentration of serum estradiol than the positive feedback response. The differential sensitivities of these two responses suggested that the tissues mediating them might also be differentially sensitive to estradiol. In a previous paper, we showed that receptor translocation is an index of estrogen sensitivity. We measured receptor translocation in response to a series of estradiol doses in the POA/AH, the MBH, and the pituitary. Dose-response curves for estrogen's effect on receptor translocation showed that the pituitary receptor translocation mechanism is activated at significantly lower levels of serum estradiol than that of either the POA/AH or the MBH. These results are consistent with the POA/AH as a site of estrogen's positive feedback effects. In addition, they suggest that negative feedback in the rat may be mediated via estrogen's action at the anterior pituitary. Estrogen's negative feedback effect on serum LH occurs at a serum level of estrogen at which no receptor is translocated in the MBH. Therefore, the pituitary, which does possess nuclear receptors at these estradiol dose levels, is more likely to be the primary mediator of estrogen's negative feedback effects. In another experiment, pituitary, but not hypothalamic, receptor was translocated to the nuclear fraction with an injection of 100 micrograms clomiphere (Clomid). Under these conditions serum LH is depressed, thus strengthening the hypothesis that, in the rat, estrogen action on the pituitary can cause suppression of serum LH independently of the hormone's action in the hypothalamus.

Electromyographic activity of the nonpregnant and pregnant sheep uterus

Myometrial electromyograms were studied in nonpregnant ewes, pregnant ewes throughout the second half of gestation, and during labor and delivery in normal spontaneous vaginal delivery and premature delivery induced by the continuous infusion of synthetic adrenocorticotropin 1-24, 1 microgram x h-1, to the fetus at 120 and 130 days' gestation. The bursts of electromyographic (EMG) activity during estrus were very similar to those seen in the pregnant ewe in the second half of gestation. In the second half of gestation, the bursts of EMG activity lasted a mean of 6.7 minutes and occurred at intervals of 54.7 minutes in utero, without an incision for fetal instrumentation, and were 7.2 minutes in duration, occurring every 46.6 minutes when the uterus had been incised. EMG activity occurred simultaneously at most recording sites within the uterus. There was no evidence to support the view that a uterine pacemaker exists with a fixed location. As delivery approached, the mean duration of each EMG burst began decreasing more than 24 hours before delivery, and the frequency of the bursts increased, demonstrating that the recording of uterine electromyograms provides a precise and sensitive method for the study of the early changes that lead to labor and delivery.

Radioimmunoassay of estradiol-17 beta in unextracted ewe plasma

A radioimmunoassay for estradiol-17 beta (E 2 beta) without solvent extraction is described. It can be used for plasma samples with concentrations higher than 10 pg/ml. Tritiated E 2 beta, and a specific antiserum in phosphate buffer were added to plasma samples, the total incubation volume being 0,5 ml. An identical volume of steroid free plasma to that assayed in unknowns (0.050 -0.2 ml) was added to the standard curve. Immunoprecipitation was used to separate bound and free E2 beta and the bound radioactivity counted in the polyproplene assay tube. The calculated regression of E2 beta measured on plasma loaded with excess E2 beta (y = 0.987x / 3.8; R = 0.99) and that of E2 beta measured in the same sample by the direct assay on that of E2 beta found by a reference extraction method (y = 0.998x / 14.9; R = 0.98) as well as the presence of parallelism between the standard curve and different volumes of plasma and acceptable inter and intra assay coefficients of variation show that this method is suitable for the measurement of E2 beta in uteroovarian venous plasma. However, this method cannot be used for peripheral plasma of pregnant animals because it is not specific. The method was found useful in a study on the effect of gonadotrophin pulses on the ovary when many samples had to be analysed. Furthermore, there is a potential for automatization which would facilitate more detailed analyses of ovarian-hypophyseal relationships.

The active immunization of the cyclic ewe against an estrone protein conjugate

Four mature, cyclic ewes were given injections (I.M.) of a conjugate of 1,3,5 (10)-estratrien-3-ol-6,17-dione, 6 carboxyoxime bovine serum albumin (immunized ewes) on day 3 after estrus, and at days 10, 20, 40, 58, 91 and 134 after this initial treatment. Six control ewes treated with carrier emulsion alone continued to cycle normally. Three of the immunized ewes failed to exhibit estrus, an associated preovulatory surge of LH and ovulation. One ewe showed 1 abnormally short estrous period and then became anestrus. Injection of an estrone-protein-conjugate at days 3 and 13 after estrus did not appear to interfere with the rate of structural luteolysis of the corpus luteum present, but plasma concentrations of progesterone reached abnormally high luteal phase levels and in 2 ewes failed, subsequently to decline to normal follicular phase levels. Estrone binding capacity rose as early as day 9 after first treatment, and concentrations of LH rose as early as day 14. Subsequently, plasma levels of LH, estrone and progesterone and antisera titer rose; the only significant cross reaction of the antisera was with estradiol 17beta (11.32 +/- 2.80%).

Periovulatory changes in ovarian temperature in ewes

Thermistors were implanted in intact ewes, and ovarian and aorta temperatures were recorded for 72 hours, following the removal of a progesterone implant intended to induce estrus. Serum levels of luteinizing hormone (LH) were measured hourly over a 10 hour period beginning at the onset of estrus. Ovaries were examined by laparotomy at the end of each experiment. Estrus behavior, LH surge, and a fresh corpus luteum were all found to be present in four, and absent in two, of a total of six experiments. To remove variations in basal body temperature, ovarian temperatures were measured relative to aorta temperature at all times. In the nonovulating ewes, both mean ovarian temperatures varied at random, whereas in the ovulating ewes they decreased by approximately 0.15 degrees C. to reach a minimum 1 hour before the time of maximum rate of increase in LH. The ovulating ovaries differed from the contralateral ovaries (where ovulation did not occur) in two respects: the mean temperature in the ovulating ovaries was lower by 0.02 to 0.10 degrees C. at all times, and its preovulatory decrease began several hours earlier. When taken in conjunction with published data on secretion and on the local and systemic effect of estradiol, these findings, are consistent with the hypothesis that ovarian estradiol induces an increase in ovarian blood flow. A heat-sink effect of the uterine mass due to its proximity to the ovaries may also be involved.

In vitro contractile activity of the mesotubarium superius from the rabbit oviduct in various endocrine states

We investigated the influence of estrogen on the contractile activity of smooth muscle in the nonpregnant female reproductive tract, using as a model isolated strips of mesotubarium superius (MTS) removed from the rabbit oviduct. We studied four physiologic states in which muscular activity was influenced to varying degrees by endogenous estrogen. Normal estrous (estrogen dominated) rabbits were used as controls. We observed decreased activity in MTS from rabbits chronically deprived of estrogen (60) days postovariectomy). However, a dramatic increase in activity occurred in response to acute withdrawal of ovarian function (12 hours postovariectomy). An increase in activity also occurred at the time of ovulation. We concluded that acute withdrawal of endogenous estrogen is a potent stimulus to reproductive smooth muscle in the female rabbit and that it might contribute to increased muscular activity at ovulation.

Influence of oestrogen on thyroid function in the ewe

1. Thyroid activation at oestrus occurs in several species, which may be related to oestrogen secretion occurring at the same time. In the ewe this relationship has been examined by measuring thyroid activity before and after oestrogen administration.2. Measurements have been made of thyroid (131)I release rate and protein-bound (131)I concentration in the plasma in normal and ovariectomized ewes and of protein-bound (125)I in plasma from thyroid vein blood in ewes with exteriorized thyroid glands.3. No evidence of an activation of the thyroid by oestrogen was observed in immature ewes or adult oestrous cycle, anoestrous or ovariectomized ewes, given oestrone or oestradiol dibenzoate in doses of 25-1000 mug by injection.4. It was concluded that oestrogen may not be responsible for thyroid activation observed in normal oestrous ewes.