Effects of progesterone and oestradiol on RNA and protein metabolism in the genital tract and on survival of embryos in the ovariectomized ewe.

The hormonal regulation of metabolism in the genital tract and the development of embryos during early pregnancy in the ewe have been examined. Ovariectomized ewes received injections of maintenance progesterone, oestrous oestradiol and priming progesterone according to schedules designed to simulate endogenous ovarian secretion during early pregnancy, around the time of oestrus and during the luteal phase of the oestrous cycle immediately preceding oestrus. The survival and development of embryos was dependent upon the dose of maintenaince progesterone and the duration of treatment at the time of transfer, but changes in progesterone dose did not change endometrial protein or RNA metabolism on particular days. Both priming progesterone and oestrous oestradiol were required for normal embryo development. Priming progesterone and oestrous oestradiol each increased endometrial RNA/DNA ratios during early pregnancy. There were no interactions between priming progesterone and oestrous oestradiol, their effects being simply additive. Neither maintenance nor priming progesterone had any effect on protein and RNA metabolism in the oviduct. It is suggested that in the intact ewe oestrogen secreted at oestrus and progesterone secreted prior to oestrus play important roles in the establishment of a uterine environment suitable for the subsequent normal development of embryos.     

Progesterone and oestrogen receptors in the female genital tract throughout pregnancy in tammar wallabies

The tammar, Macropus eugenii, is a monovular macropodid marsupial which has a post-partum oestrus and an 11 month embryonic diapause. Progesterone and oestradiol cytosol receptors were measured by Scatchard analyses and single point analysis in the lateral vagina, endometrium and myometrium of the gravid and contralateral non-gravid uterus throughout pregnancy, immediately after parturition and during seasonal reproductive quiescence. In endometrial tissues, both progesterone and oestradiol receptors doubled in concentration in both gravid and non-gravid uteri between day 0 and day 5 of pregnancy, coinciding with previously described peak values in peripheral plasma progesterone and oestrogen. Receptor concentrations in endometrial tissue during seasonal quiescence were not significantly different from those immediately after reactivation. After day 12 of pregnancy, downregulation of both progesterone and oestradiol cytosolic receptors occurred concomitant with the increase in progesterone in the peripheral plasma. However, there was a unilateral increase in oestradiol receptor concentrations in endometrium obtained from the non-gravid uterus between day 25 of the 26.5 day gestation and immediately after parturition. Myometrial receptor concentrations mirrored those of the endometrium but were lower. Concentrations of progesterone receptor in the lateral vaginae were at the lower limit of detection, while the oestradiol cytosol receptor concentrations were even lower in this tissue. Thus, the steroid receptor concentrations provide another example of local unilateral endocrine responses in the reproductive tract of the tammar. These results also indicate that the downregulation of progesterone and oestradiol receptors that occurs in both uteri in mid- and late-pregnancy is selectively and locally reversed before parturition in the non-gravid endometrium in response to the local effects of follicular oestradiol from the ipsilateral ovary.     

Increased uterine uptake and nuclear retention of [3H]oestradiol through the oestrous cycle and enhanced end-organ sensitivity to oestrogen stimulation in vitamin B6 deficient rats

Vitamin B6 deficient female rats showed a significantly earlier, greater and more prolonged uptake of a tracer dose of [3H]oestradiol into the uterus, with increased nuclear accumulation, compared with vitamin B6 supplemented animals. This was most marked at oestrus, with little difference at anoestrus. The responses to low doses of ethynyl-oestradiol were greater in ovariectomized deficient animals than in those receiving the supplemented diet, with an increased uterotrophic response and greater induction of peroxidase. In the deficient animals there was virtually complete suppression of LH secretion at doses of ethynyl-oestradiol that had no effect in controls. At high doses of ethynyl-oestradiol there was no difference between the two groups of animals. The results suggest that increased uterine uptake and accumulation of [3H]oestradiol in vitamin B6 deficiency is associated with enhanced end-organ responsiveness to sub-maximal oestrogen stimulation, and that pyridoxal phosphate may have a coenzyme role in oestrogen action.     

Control of oestrus in cattle using progesterone coils

Four experiments were conducted to determine the effect of length of treatment, stage of cycle at start of treatment and administration of oestradiol benzoate or progesterone at the start of treatment with intravaginal progesterone coils on oestrous response and fertility. In Experiment 1, the number of heifers in oestrus was affected neither by injection of 5 mg oestradiol benzoate alone or with 200 mg progesterone nor by length of treatment. More heifers (P < 0.05) were in oestrus on day 2 after treatment following a 12-day treatment compared to a 9-day treatment.In Experiment 2, heifers between days 17 and 20 of the oestrous cycle received an injection of either 5 mg oestradiol benzoate alone or with 200 mg progesterone at the start of a 9-day treatment with progesterone coils. Neither the number of heifers in oestrus nor the pattern of onset were affected after treatment. In Experiment 3, heifers between days 0 and 3 of the oestrus cycle received progesterone coils for 9, 12 or 14 days. In addition, animals received (i) no further treatment, (ii) a gelatin capsule adhered to the coil containing 10 mg oestradiol benzoate (iii) a gelatin capsule adhered to the coil containing 200 mg progesterone. Following a 9- or 12-day treatment period heifers receiving the coil with the oestrogen capsule had a high oestrous response ( compared to , P < 0.05). When oestrogen was not given, there was a significant linear effect of duration of treatment on the number in oestrus (9 days, ; 12 days ; 14 days, ; P < 0.05).In Experiment 4, post-partum cows were used to compare a 9- and 12-day treatment period and half the animals in each group received either 5 mg oestradiol benzoate and 200 mg progesterone at the start of treatment or a 10 mg gelatin capsule adhered to the coil. The length of treatment affected the number of heifers in oestrus since were in oestrus after a 12-day treatment period compared with after a 9-day period (P < 0.001). There were no significant differences in the number of cows in oestrus after injection of oestrogen and progesterone ( ) or after the use of the gelatin capsule ( ).     

Uterine oxytocin receptors in cyclic and pregnant cows.

Binding of [3H]oxytocin to uterine subcellular preparations ('oxytocin receptor concentrations') was measured in uterine tissue of heifers and multiparous dairy cows at various stages of the oestrous cycle and during early pregnancy. A method for the assay of ovine uterine oxytocin receptors was optimized for use on bovine tissue. Oxytocin receptor concentrations were increased in cyclic animals around the period of luteolysis and oestrus, rising on Day 15 in endometrium and on Day 17 in myometrium while pregnant animals showed no comparable rise. Receptor concentrations then declined on Day 3 after oestrus in myometrium and on Day 5 in endometrium. Some cyclic animals did not show the expected rise in receptors in the late luteal phase; these animals had abnormally high progesterone concentrations for this stage of the cycle. In animals slaughtered on Day 18 after oestrus and/or insemination which had low oxytocin receptor levels, plasma progesterone concentrations were consistently high; while all animals showing the late luteal phase elevation in receptor values had low progesterone concentrations. Oxytocin receptor and progesterone concentrations were negatively correlated (P less than 0.05). These data support the hypothesis that oxytocin receptor level is a key factor in the process of luteolysis in cattle and that in pregnancy there is suppression of uterine oxytocin receptor at the expected time of luteolysis. We suggest that uterine oxytocin receptor levels are partly controlled by circulating steroid hormones and are suppressed during early pregnancy.     

Influence of the oestrous cycle on L-glutamate and L-aspartate transport in rat brain synaptosomes.

Oestrous cycle and sex differences in sodium-dependent transport of L-[3H]glutamate and L-[3H]aspartate were investigated employing well washed synaptosomes prepared from rat brain cortex. Transport was best analysed on the basis of two components, a high and low affinity transport site. Oestrous cycle and sex differences were observed for both substrates. The high affinity transporter displayed highest affinity for glutamate transport in synaptosomes from female rats during proestrous and oestrous. This differed significantly from glutamate transport during dioestrous and in male rats. High affinity aspartate transport displayed highest affinity during oestrous and differed significantly from transport during dioestrous. Maximal velocity of high affinity glutamate transport was higher in synaptosomes from females during dioestrous compared with oestrous and lower in synaptosomes from male rats when compared with female rats in dioestrous and metoestrous. The low affinity sodium-dependent glutamate transporter displayed a 10-fold higher affinity for glutamate during proestrous than during the other three phases of oestrous and in male rats. Exogenously applied oestradiol and progesterone to synaptosomes from male rats showed no effect on glutamate or aspartate transport. No acute effect of oestradiol or progesterone on glutamate currents in oocytes expressing EAAT1 or EAAT2 subtype of glutamate transporter was observed. These results suggest hormonal regulation of high and low affinity sodium-dependent excitatory amino acid transporters over the four day oestrous cycle in synaptosomes from rat cortex. This regulation is unlikely to be due to a direct effect of oestradiol or progesterone on glutamate transporters.     

Cervical mucus and oestrous behaviour responses to oestrogens in sheep: Progesterone-oestrogen relationships and role of progesterone pre-treatment

The final dose of progesterone (5, 10, 20 mg) and time to oestrogen injection relative to the final dose of progesterone (24–72 h) had no significant effect on the production of cervical mucus measured 24 h after the injection of 30 μg oestradiol benzoate (ODB). However, there were significant effects on the behavioural oestrous responses (time from injection of oestrogen to onset of oestrus and duration of oestrus). Time to onset of oestrus increased from 18 to 27.8 h with increasing dose of progesterone (P < 0.001) and decreased from 24.8 to 20 h with increasing time to oestrogen injection (P < 0.05). Conversely, the duration of oestrus decreased from 36.2 to 23.8 h with increasing dose of progesterone (P < 0.001) and increased from 29 to 39 h with increasing time to oestrogen injection (P < 0.01).Ovariectomized ewes became refractory to ODB as measured by the cervical mucus response after the fifth sequential daily injection of 20 μg oestradiol benzoate. Progesterone priming was not required to restore subsequent sensitivity to oestrogen treatment. However, there was a positive linear relationship between length of recovery period and level of response to subsequent treatment.It was concluded that: (1) progesterone pre-treatment or priming is not necessary in the cervical mucus bioassay in ovariectomized ewes; and (2) a period of 8–16 days is needed between assays for normal sensitivity to be regained.     

Changes of progesterone content of rat uterine flushings in relation to serum concentrations of progesterone during the oestrous cycle.

Uterine fluid was collected from four-day cyclic rats at each stage of the oestrous cycle and assayed for progesterone and protein content. Progesterone was determined by radioimmunoassay either after ethanol (or 2.5% NaOH) denaturation of proteins from uterine flushings ('total' progesterone) or without protein denaturation ('ether-extractable' progesterone). The amount of 'ether-extractable' progesterone in the lumen was constant from metoestrus to pro-oestrus (340 pg per uterus) but lower in oestrus (200 pg per uterus). However, 'total' progesterone content of uterine fluid was subject to cyclic variations and was highest in dioestrus (890 pg per uterus) and lowest in oestrus (350 pg per uterus), in contrast to serum progesterone which is lowest in dioestrus and highest in oestrus. Protein content of uterine flushings peaked to 780 micrograms per uterus in pro-oestrus then fell to about 140 micrograms per uterus until the end of the oestrous cycle. Changes in protein content of the lumen were followed by qualitative variations since the mean amount of 'bound' progesterone ('total' progesterone minus 'ether-extractable' progesterone) released per milligram of denatured lumen protein rose from 1.8 pmol in pro-oestrus to 18.2 pmol in dioestrus. The changes of luminal 'bound' progesterone during the oestrous cycle suggest that progesterone binding to luminal proteins could be an important modulator of progesterone action in rat uterus. Moreover, the variations in progesterone content of the lumen, irrespective of serum progesterone concentrations, are consistent with the hypothesis that progesterone synthesis occurs in the uterus.     

Characterization of uterine sex steroid receptors in the pig and their variation during the oestrous cycle

The present study establishes and validates an in vitro binding and exchange assay for tissue receptors for oestradiol (E) and progesterone (P) in pig uterus. Both hormones bound to specific cytoplasmic (Rc) and nuclear (Rn) receptor proteins with high affinity. The relative concentrations of the receptors were measured in dissected samples from endometrium and myometrium obtained at late prooestrus, oestrus, and luteal phases of the oestrous cycle. The Scatchard analysis of the oestradiol and R 5020-receptor complex displayed linearity and indicated a single class of high affinity, low capacity binding sites. Significant variations were seen in the binding of E and P to their cytosolic and nuclear receptors, following the changes in the circulating levels of the hormones in blood plasma during the oestrous cycle. Both tissue components, i.e. endometrium and myometrium followed a similar pattern when related to the stage of the oestrous cycle considered. The ERc increased from prooestrus, reaching a maximum at standing oestrus, thereafter decreasing. The concentration of ERn increased from prooestrus towards the early luteal phase, with a significant reduction by day 8 of the cycle. The amounts of PRc were maximal at standing oestrus, remaining high during the early luteal phase, while the PRn showed a linear increase from oestrus onwards throughout the luteal phase.     

Endometrial protein secretion during early pregnancy in entire and ovariectomized ewes

The secretion and synthesis of protein in vitro by explants of endometrium were examined in entire ewes during the first 10 days of the oestrous cycle and during an equivalent interval in ovariectomized ewes which received injections of oestradiol and progesterone. The schedule of steroid injections given was designed to simulate endogenous ovarian secretion of progesterone during the luteal phase before oestrus, of oestradiol around oestrus and of progesterone during the luteal phase after oestrus. The rate of protein synthesis and tissue RNA:DNA and protein:DNA ratios in intercaruncular and caruncular endometrium were generally higher in entire than in ovariectomized ewes. In ovariectomized ewes oestradiol increased these activities at 2-4 days after oestrus, whereas progesterone preceding oestradiol caused increases at oestrus, but not thereafter. In entire ewes and in ovariectomized ewes receiving the full steroid treatment regimen, protein secretion was high at oestrus and declined markedly during the next 4-6 days. In ovariectomized ewes not receiving progesterone before oestradiol, secretion increased between 4 and 6 days after oestrus, or during the equivalent stage of treatment in ewes which did not show oestrus. The omission of this progesterone did not modify secretion by caruncular endometrium. Oestradiol increased protein secretion by both tissues. The data suggest that progesterone given before oestradiol (or its equivalent in entire ewes) inhibits the secretion, at about 4-7 days after oestrus, of uterine proteins which may impair embryo development in ovariectomized ewes which do not receive this progesterone.     

Oestrous and ovarian responses to exogenous progesterone and oestrogen in prepubertal ewe lambs in relation to the fecundity of their dams

Oestrus was consistently induced by 20, 40 or 80 microgram oestradiol benzoate in progesterone-primed lambs aged 23 weeks and 17 weeks respectively in two experiments. The duration of oestrus increased linearly with increasing log dose of oestrogen, and was negatively correlated with the time of its onset. In the absence of progesterone there was a reduced incidence, later onset and shorter duration of oestrus. Progesterone alone did not induce oestrus. In lambs treated during January (Exp. 2), a later date of injection of oestrogen was associated with earlier onset and longer duration of oestrus. The induced oestrus was anovulatory. Oestrogen reduced the proportion of lambs with follicles greater than or equal to 3 mm in diameter whilst progesterone had no effect. Lambs which were the progeny of low- and high-fecundity dams did not differ in their oestrous or ovarian responses. Correlations between the dam's lamb production index and the time to onset and duration of the induced oestrus were also not significant.     

Prolactin as a factor in the uterine response to progesterone in rabbits

The direct effect of prolactin on uteroglobin production and on uterine endometrial oestrogen and progesterone receptor concentrations was tested by using ovariectomized rabbits (at least 12 weeks) treated with prolactin; prolactin + progesterone; prolactin + oestradiol + progesterone; oestradiol + progesterone; or progesterone alone. Prolactin treatment produced a significant (P less than 0.05) increase in the concentration of cytosolic oestrogen and progesterone receptors, restoring the concentrations to values found at oestrus. However, the concentration of nuclear receptors remained low. In the remaining treatment categories there was no significant (P greater than 0.05) increase in the concentration of oestrogen and progesterone receptors compared with those in ovariectomized controls. However, the sequential treatment of ovariectomized animals with prolactin + progesterone stimulated uteroglobin production to a concentration equal to that found in intact rabbits on the 5th day of pregnancy. This was not achieved by prolactin or progesterone alone or with oestradiol. These results suggest that prolactin acts as an essential factor in the rabbit uterine response to progesterone, perhaps by the modulation of progesterone receptor activity.     

Plasma hormone levels and reproductive behaviour in anoestrous ewes after treatment with progesterone and PMSG

Plasma progesterone and gonadotrophin levels were studied in anoestrous ewes treated during June or July with a subcutaneous progesterone implant and/or an injection of oestradiol or PMSG. Of 32 ewes treated with progesterone during July, 9 showed a gonadotrophin surge after removal of the implant, and 10 ewes showed oestrous behaviour during the following 4 days. Six ewes conceived at this induced oestrous. Progesterone treatment during June was much less effective, with only 2 of 19 treated ewes showing a gonadotrophin surg and oestrous behaviour. Administration of PMSG at the time of implant removal in the June experiment was followed by a gonadotrophin surge and oestrous behaviour in 18 of 19 ewes, and 15 ewes conceived at the induced oestrus. An injection of PMSG, without progesterone pretreatment, stimulated a gonadotrophin surge and ovulation, but did not result in oestrous behaviour. The treatments employed appeared to initiate cyclic ovarian activity in the July experiment, but not in the June experiment.     

Changes in the density of peripheral benzodiazepine binding sites in genital organs of the female rat during the oestrous cycle

The affinity and the density of peripheral-type benzodiazepine binding sites (PBzS) in tissues from the genital organs of female rats were studied during the oestrous cycle. When comparing PBzS density on the day of oestrus to PBzS density on the day of pro-oestrus, a significant increase was observed in the ovary (1.9-fold), oviduct (2.4-fold) and uterus (1.7-fold), but not in the kidney. Serum oestradiol also increased to a maximum on the day of pro-oestrus. The ovarian and uterine PBzS density and serum concentrations of oestradiol and progesterone were measured every 8 h between the days of dioestrus and pro-oestrus. Ovarian and uterine PBzS density increased to a maximal value at 01:00 and 09:00 h, respectively, on the day of pro-oestrus. However, a significant increase in PBzS density occurred in the ovary (P less than 0.02) and uterus (P less than 0.001) at 09:00 h on the day of pro-oestrus as compared to 09:00 h on the day of dioestrus. These changes were associated with an increase in serum oestradiol and progesterone concentrations. The affinity of PBzS in all tissues examined remained unaltered during the oestrous cycle. This study demonstrates that changes associated with the oestrous cycle occur in the density of PBzS in various genital organs.     

Induction of ovulatory oestrus in true anoestrous buffaloes during low breeding season

A fertility treatment trial of anoestrous buffaloes was undertaken on a well managed dairy farm in the low breeding season. Forty lactating buffaloes, 12 each from first and second parity and 16 from third or higher parity, not seen in oestrus for at least 3 to 5 months were diagnosed anoestrous by rectal examination. A subcutaneous ear implant containing 3 mg of norgestomet was inserted, accompanied by an intramuscular injection of 3 mg norgestomet and 5 mg of oestradiol valerate (Syncro-mate B, Intervet). After 9 days the implant was removed and 600 IU of PMSG (Intervet) were given intramuscularly. Irrespective of oestrous behaviour, the animals were inseminated with frozen semen at two fixed times: 48 and 72 h after removal of the implant. Thirty animals having calved in the same period as the experimental animals and not seen in oestrus since then served as controls. Milk samples for progesterone analysis were taken on the day of insertion of the implant, the day of removal and on days 10 and 22 after the second A.I. Progesterone determination by means of an enzyme immunoassay (EIA) revealed that 33 buffaloes out of 40 (82.5%) were in true anoestrus. Ovulation occurred in 21 buffaloes out of 30 (70%). Three buffaloes could not be followed up further. The overall conception rate was 53.3%. The parity-wise conception rate was 40%, 44.4% and 72.2% in first, second and third or higher parity, respectively. None of the control animals displayed oestrus during the course of the study.     

Luteinizing hormone, oestrogen and progesterone levels in peripheral serum of anoestrous and cyclic ewes as determined by radioimmunoassay.

Jugular vein blood was collected daily from four mature ewes throughout anoestrus and the first oestrous cycle of the breeding season until 4 days after the second oestrus. The levels of oestrogen, progesterone and LH were determined by radioimmunoassay. There were fluctuations in the LH level throughout most of the observed anoestrous period with a mean plus or minus S.E. value of 2-3 plus or minus 0-9 ng/ml. High LH values of 20-0, 41-2 and 137-5 ng/ml were observed in three ewes on Day - 24 of anoestrus. A brief minor rise in progesterone level was also observed around this period. Progesterone levels were consistently low (0.11 plus or minus 0-01 ng/ml) before Day - 25 of anoestrus. A major rise occurred on Day - 12 of anoestrous and this was followed by patterns similar to those that have been previously reported for the oestrous cycle of the ewe. Random fluctuations of oestrogens deviating from a mean level of 4-40 plus or minus 0-1 pg/ml were observed during anoestrus and the mean level during the period from the first to the second oestrus was 5-2 plus or minus 0-3 pg/ml. A well-defined peak of 13-3 plus or minus 0-7 pg/ml was seen in all ewes on the day of the second oestrus. Results of the present study suggest that episodic releases of LH occur during anoestrus and periods of low luteal activity. The fluctuations in LH levels, as observed during the period of low luteal activity, i.e. before Day - 25 of anoestrus, were less pronounced during the periods of high luteal activity. The view that luteal activity precedes the first behavioural oestrus of the breeding season is supported.     

Influence of progesterone and oestradiol-17 beta on blastocysts of the tammar wallaby (Macropus eugenii) during seasonal diapause

Forty tammar wallabies, presumed to be carrying quiescent blastocysts, were injected with progesterone and oestradiol alone, or in combination, during seasonal quiescence when the corpus luteum is inactive. Plasma progesterone concentrations were increased to values equivalent to those of late pregnancy for the duration of the treatment in progesterone-treated groups but otherwise remained at values equivalent to seasonal quiescence. Tammars treated with low doses of oestradiol showed no measurable increase in plasma oestradiol concentrations but in those treated with high doses plasma concentrations were increased to oestrous levels. At autopsy on Day 18 after the start of treatment the embryos and reproductive tracts were assessed. While progesterone alone caused reactivation of about 50% of the embryos, blastocysts in tammars treated with oestradiol alone remained in diapause (low dose) or disappeared from the uterus (high dose): 2 blastocysts collapsed after some slight expansion. No synergistic effect on pregnancy was noted in tammars receiving both oestradiol and progesterone. We conclude that oestrogen alone is not capable of stimulating normal growth of blastocysts, and its role during early pregnancy in tammars remains unclear.     

Oestradiol and progesterone receptors in the pig oviduct during the oestrous cycle

The concentrations of the tissue receptors for oestradiol (E) and progesterone (P) in the porcine oviduct at different stages on the oestrous cycle have been investigated by in vitro binding and exchange methods. Both hormones bound to specific cytoplasmic (Rc) and nuclear (Rn) receptor proteins with high affinity. The concentrations of ERc and ERn were two-fold higher in the ampulla as compared to the isthmus. The amount of ERc in the isthmic portion of the oviduct did not vary throughout the oestrous cycle. However, the ampullar ERc concentrations increased during prooestrus, showed a maximum at standing oestrus, thereafter decreasing. Significant variations in the amount of oviductal ERn were observed. Despite the differences in ERn amounts between segments, the concentration of ERn increased significantly during late prooestrus, attaining a three-fold elevation and remaining elevated during the period of standing oestrous and early luteal phase (days 3-4), thereafter returning to basal levels. No significant variations in the amount of isthmic PRc were found throughout the period studied. The ampulla, however, showed a significant increase in PRc concentrations during standing oestrus, thereafter decreasing. The concentrations of PRn in isthmus and ampulla were of about the same magnitude and varied significantly during the oestrous cycle, increasing in concentration from standing oestrous onwards. The temporal relationships between the variations in levels of oestradiol and progesterone receptors in oviductal tissues and those of the circulating plasma levels were established. The data obtained in this study suggest a relationship between the changes in the levels of oestradiol and progesterone oviductal binding during the first days of the oestrous cycle, and the gamete and embryo transport throughout the oviduct in the porcine species.     

Oestrogen and progesterone receptor immunoreactivity and c-fos expression in the ovine cervix.

Immunocytochemistry was used to detect the presence of oestrogen and progesterone receptors in the cervices of prepubertal lambs, seasonally anoestrous ewes, cyclic ewes, and pregnant ewes of known gestational stages, to define the roles of gonadal steroids in cervical function. The presence of the immediate early gene product, c-Fos, a marker for cellular activation, was also investigated using immunocytochemistry and in situ hybridization. Oestrogen receptor immunoreactivity was restricted to the endometrium on days 0-3 of the oestrous cycle (day 0 = oestrus). In immature animals, very few scattered nuclei in the endometrium were immunoreactive. Oestrogen receptor immunoreactivity was not apparent in the endometrium during the remainder of the oestrous cycle or in this region in anoestrous animals. In pregnant ewes, oestrogen receptor immunostaining appeared as relatively few isolated nuclei in the connective tissue stroma. Progesterone receptor immunoreactivity was found in the endometrium at days 0-3 of the oestrous cycle and also in the luminal epithelium, the myometrium and the blood vessels. Progesterone receptor immunoreactivity was also found in these regions, with the exception of the endometrium, at all other stages examined. Immunostaining for c-Fos was present in the endometrium at days 0-3 of the oestrous cycle, and some scattered immunopositive nuclei were present in prepubertal animals. c-Fos immunoreactivity was also found in the myometrium and in blood vessels at all other stages examined. Visualization of c-fos gene expression by in situ hybridization showed that it occurred in the luminal epithelium and blood vessels at oestrus, but was restricted to the blood vessels in all other samples examined.     

Hormonal control of pinocytosis in the uterine epithelium of the rat.

Ovariectomized rats were treated with oestradiol-17 beta and/or progesterone to mimic the hormonal parameters inducing uterine sensitivity for implantation. The degree of pinocytosis of trypan blue and ferritin in the endometrial cells was examined. Significant epithelial pinocytosis of trypan blue occurred after a 3-day treatment of progesterone, and uptake was independently increased by priming with oestrogen and by oestradiol given on the 3rd day of progesterone treatment. Progesterone treatment caused uptake of ferritin by the epithelial cells; in control animals epithelial and stromal cells were involved. Oestrogen priming enhanced ferritin absorption, while 'nidatory' oestrogen had no effect. Oestradiol given alone completely blocked pinocytosis of both intraluminally injected substances.