Differences in the rabbit uterine response to progesterone as influenced by growth hormone or prolactin

The direct effect of growth hormone (GH) on the uterine response to progesterone was tested by using ovariectomized rabbits (at least 12 weeks) treated with GH; GH + progesterone; or progesterone alone. These results were compared with the effect of prolactin or prolactin + progesterone on the uterus. Prolactin treatment produced an increase (P less than 0.01) in the endometrial surface area and restored cytosolic oestrogen and progesterone receptor concentrations to oestrous control values. The sequential treatment of does with prolactin + progesterone stimulated uteroglobin production to a concentration equal to that found in intact rabbits on Day 5 of pregnancy. In contrast, GH treatment had no effect on endometrial surface area, produced an increase in the concentration of cytosolic oestrogen receptor but did not produce an increase in the concentration of progesterone receptor. The sequential treatment of does with GH + progesterone failed to stimulate uteroglobin secretion above control (progesterone alone) values. It is concluded that the action of prolactin in the rabbit uterus is no generally somatogenic; rather, prolactin increases the concentration of progesterone receptor and thereby enhances the uterine response to progesterone.     

Variability in the response of the rabbit uterus to progesterone as influenced by prolactin

Ovariectomized rabbits from different breeders were treated at different times of the year with prolactin alone or with progesterone and the production of uteroglobin by the uterus was studied. There were seasonal, strain and dose variables in the uterine response to prolactin and progesterone. Treatment with prolactin (at 1 mg/day) plus progesterone generally induced higher levels of uteroglobin production than did treatment with progesterone alone. The differences were greatest in the winter for Tennessee animals and in the spring for animals from the New Mexico and North Carolina colonies. Ovariectomy produced a decrease (P less than 0.01) in the concentration of cytosolic oestrogen and progesterone receptors, and prolactin treatment restored the concentration to oestrous control values. However, there were no seasonally dependent changes in the concentration of the receptors for any of the treatment groups. Increased doses of prolactin (2 mg/day) induced high levels of uteroglobin production and new proteins to appear in uterine secretions of long-term ovariectomized rabbits but much lower levels (10-11%) when given to pregnant does. Additional ovulations were also noted plus adverse effects on the embryos.     

Prolactin enhances uteroglobin gene expression by uteri of immature rabbits

The effect of prolactin on uteroglobin production by immature rabbits was studied with neonatal (1 day old) and juvenile (14 days old) does. The animals were divided into 11 treatment groups for each age category and exposed to a 9-day injection protocol. Each day the animals received a subcutaneous injection of oestradiol-17 beta and/or ovine prolactin and/or progesterone, or were sham-injected. Juvenile animals, which received 100 micrograms oestradiol/kg 24 h-1, plus progesterone or plus prolactin and progesterone, produced detectable amounts of uteroglobin in the uterine secretions (0.034 +/- 0.010 mg uteroglobin/mg total protein and 0.098 +/- 0.03 l mg uteroglobin/mg total protein, respectively). None of the animals in the other juvenile treatment groups or any of the neonatal groups produced uteroglobin. From this survey it was apparent that uteroglobin secretion could be induced by exogenous oestradiol and progesterone in rabbits treated as early as 14 days of age, and that the added supplementation of prolactin enhanced the response to the ovarian steroids. As a result, additional juvenile animals were injected with 100 micrograms oestradiol +/- prolactin + progesterone and the effects of these two treatments were quantitated as follows: uteroglobin mRNA levels by slot-blot hybridization; endometrial surface area by computerized image analysis; and oestrogen, progesterone and prolactin receptors by immunocytochemistry. Prolactin modified the response of the juvenile rabbit uterus to oestradiol + progesterone for all parameters tested.     

Servomechanism of prolactin and progesterone in regulating uterine gene expression

To investigate the interaction of PRL and progesterone in regulating uterine gene expression, we have quantitated the concentration of PRL receptor and of uteroglobin (UG) mRNA in the endometrium of rabbits of different ages and after treatment with different hormones. During uterine differentiation in 2- to 4-week old rabbits, a marked increase in unoccupied uterine PRL receptor number was observed, presumably increasing uterine sensitivity to PRL. Receptor values for 4-week old rabbits were comparable to values for sexually mature, estrous females, but were lower than in 5-day pseudopregnant (PSP) animals. When total PRL receptor was determined by Scatchard analysis after in vitro desaturation with MgCl2, PSP animals again expressed the highest receptor concentration with no changes in the dissociation constant (Kd) values. To determine whether progesterone regulates uterine PRL receptor, long term ovariectomized rabbits (greater than 12 weeks) were treated with various combinations of hormones, and unoccupied and total uterine PRL receptors were determined. Progesterone treatment resulted in the highest concentration of both unoccupied and total PRL receptor after desaturation and removal of anti-ovine PRL antibodies with MgCl2. The value for total uterine PRL receptor was equivalent to the value for mammary gland, and the Kd values (2-4 x 10(-10) M) were similar. Treatment of long term ovariectomized rabbits with progesterone, with or without estradiol, produced an increase (P less than 0.05) in the UG mRNA content, which also occurred in PSP animals. PRL alone had no effect on UG mRNA but PRL plus progesterone increased (P less than 0.05) UG mRNA in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increases in the oxytocin-induced prostaglandin F2 alpha response and reduction in the concentrations of endometrial oxytocin receptors in ewes in response to progesterone.

Ovariectomized ewes were given progesterone and oestrogen priming as steroid pretreatment and subsequently treated with progesterone, prostaglandin F2 alpha (PGF2 alpha), or both. In Expt 1, plasma concentrations of the metabolite 13,14-dihydro-15-keto-PGF2 alpha (PGFM) were measured after an i.v. injection of oxytocin. There was little PGFM response in the untreated control ewes or in the pretreated ewes. Treatment with PGF2 alpha alone had no effect (P greater than 0.05), whereas treatment with progesterone either alone or with PGF2 alpha significantly (P less than 0.05) increased the uterine PGFM response to oxytocin. In Expt 2, chronically ovariectomized ewes had high concentrations of endometrial oxytocin receptors. Treatment with PGF2 alpha alone did not alter the concentrations of the receptors. Treatment with progesterone either alone or with PGF2 alpha significantly (P less than 0.05) reduced the concentrations of the receptors. It is concluded that progesterone promotes the PGFM response to oxytocin, but simultaneously suppresses the concentrations of endometrial oxytocin receptors.     

Effects of prolactin on conceptus survival and uterine secretory activity in pigs

Hypoprolactinaemia was induced by bromocriptine (CB154; 100 mg/day) which decreased circulating prolactin by 40% (P less than 0.06), but did not affect conceptus survival at Day 25 when administered on Days 10-16 when compared to saline:ethanol-treated control gilts. Bromocriptine or vehicle was administered to cyclic gilts on Days 10-11, oestradiol valerate was injected on Day 11 and uterine flushings were collected on Day 12. Total recoverable protein and uteroferrin in uterine flushings were not affected by treatment. However, leucine aminopeptidase activity (P less than 0.02) and total recoverable Ca2+, Na+, K+ and Cl- (P less than 0.05) were decreased in uterine flushings of gilts that received bromocriptine, suggesting that hypoprolactinaemia decreased general secretory activity of the endometrial epithelium and modulated ionic changes, respectively, in the uterine environment of pigs. Subcutaneous administration of pig prolactin (1 mg/12 h) increased (P less than 0.001) serum prolactin 4.5-fold. The interaction between hyperprolactinaemia and progesterone, without oestrogen, on components of uterine flushings were determined using gilts that received progesterone (200 mg/day) and prolactin or saline on Days 4-14 after ovariectomy on Day 4. On Day 15, there were no differences (P greater than 0.05) in any of the uterine secretory components measured. Hyperprolactinaemia (1 mg pig prolactin on Days 6-11) enhanced overall uterine secretory response on Day 12 to oestradiol (5 mg) administered on Day 11 compared to gilts that received 1 ml saline on Days 6-11 of the oestrous cycle. Total recoverable protein and leucine aminopeptidase activity were greater (P less than 0.05) for oestradiol-treated gilts, but effects of prolactin were not significant. Total recoverable glucose (P less than 0.01), PGF-2 alpha (P less than 0.02), uteroferrin (P less than 0.01) and specific activity of uteroferrin (P less than 0.001) were increased by prolactin and oestradiol, but not oestradiol alone. Calcium (P less than 0.05), chloride (P less than 0.05) and potassium (P less than 0.01) were increased in response to oestradiol. These results indicate an interaction between oestradiol and prolactin, but not progesterone and prolactin, which enhances secretion of some products of the pig uterine endometrium.     

Seasonal changes in oestrogen receptor affinity in the domestic rabbit, Oryctolagus cuniculus

Over the course of 1 year the Ka value of uterine oestrogen receptor for oestradiol varied 10-fold from a low of 0.259 +/- 0.065 X 10(9) M-1 in early spring to 2.21 +/- 0.21 X 10(9) M-1 in fall. There were no significant changes in receptor number. In addition, administration of oestradiol or progesterone to ovariectomized rabbits resulted in significant reductions in measureable oestrogen receptor affinity. Although these variations in oestrogen receptor Ka values parallel reproductive success in the domestic rabbit, no causal relationship has been established.     

Immunization of ovariectomized ewes against progesterone, oestrogen or cortisol to detect effects of adrenal steroids on reproduction

Ovariectomized ewes were immunized against cortisol, oestrogen or progesterone to determine whether steroids of non-ovarian origin occur in sufficient amounts to influence the reproductive system. Ewes immunized against oestrogen (oestrone + oestradiol) had smaller uteri (P less than 0.05) and a lower concentration of oestradiol in uterine tissue (P less than 0.05), while the adrenal gland was heavier (P less than 0.05). In the peripheral plasma of immunized ewes, the concentration of FSH, but not LH, was increased (P less than 0.05). Ewes immunized against cortisol also had smaller uteri (P less than 0.05) and heavier adrenal glands (P less than 0.05), but gonadotrophins and the concentration of oestradiol in the uterus were unaffected. Immunization against progesterone, or injection with synthetic glucocorticoids, did not affect any of the characteristics measured. We conclude that the adrenal gland of the ewes produced sufficient oestrogen or aromatizable androgen to have significant effects on the reproductive system. In contrast, adrenal production of progesterone did not produce detectable biological effects. Immunization against cortisol did affect the reproductive system, but the mechanism of this action could not be determined.     

Role of progesterone and oestradiol in the regulation of uterine oxytocin receptors in ewes.

The interaction between oestrogen and progesterone in the regulation of the uterine oxytocin receptor in sheep was evaluated by measuring the binding of oxytocin to membrane preparations of caruncular and intercaruncular endometrium and myometrium. Ovariectomized ewes were assigned in groups of five to each cell of a 4 x 2 factorial design. The four treatments were (a) vehicle (maize oil) for 12 days, (b) progesterone (10 mg day-1) for 9 days, (c) progesterone for 9 days followed by maize oil until day 12 and (d) progesterone for 12 days. The two oestradiol treatments consisted of the administration of implants in the presence or absence of oestradiol. The ewes were killed on day 10 (group b) or day 13 (groups a, c and d) for collection of uterine tissues. The response of the caruncular and intercaruncular endometrium to the treatments was similar. In the absence of oestradiol, treatment with progesterone continuously for either 9 or 12 days reduced the concentration of the oxytocin receptor in comparison with both the control and the progesterone withdrawal group (in which values were similar). The presence of oestradiol reduced the receptor concentrations in control and both 9- and 12-day continuous progesterone treatment groups, but enhanced the concentration in the progesterone withdrawal group. The myometrial oxytocin receptors responded in a similar way to those in the endometrium to progesterone treatment alone, but the addition of oestradiol produced no further effect. In conclusion, progesterone and oestradiol caused downregulation of the endometrial oxytocin receptor. On the other hand, progesterone withdrawal, similar to that which occurs during luteolysis, increased receptor density in the presence of oestradiol. Progesterone may influence the response of the myometrium to oxytocin by causing a reduction in receptor density.     

Isolation of a plasma protein observed in patients with essential hypertension

Daily progesterone administration (1.33 mg/kg body weight) to immature rabbits brought about an initial increase in the uterine content of uteroglobin which, however, subsided when progesterone treatment was continued for 10 days. During this treatment period progesterone did not lose its own uterine receptors nor did it lose its inhibitory effect on the accumulation of occupied nuclear estrogen receptors. Since immature rabbits were used, the decrease of uteroglobin concentration cannot be explained by inhibitory effects of endogenous estrogens. The results suggest that termination of uteroglobin secretion may be a selective and inherent effect of progesterone itself.     

Control of endometrial oxytocin receptor and uterine response to oxytocin by progesterone and oestradiol in the ewe

The effects of administration of progesterone and oestradiol on ovine endometrial oxytocin receptor concentrations and plasma concentrations of 13,14-dihydro-15-keto prostaglandin F-2 alpha (PGFM) after oxytocin treatment were determined in ovariectomized ewes. Ewes received progestagen pre-treatment, progesterone and/or oestradiol in 11 different treatment schedules. Progestagen pre-treatment decreased oxytocin receptor concentrations in endometrium from ewes treated subsequently with either progesterone for 5 days or progesterone for 5 days plus oestradiol on Days 4 and 5 of progesterone treatment. Oestradiol increased endometrial oxytocin receptor concentrations when administered on Days 4 and 5 of 5 days progesterone treatment. Progestagen pre-treatment followed by progesterone treatment for 12 days caused a large increase in oxytocin receptors and no further increase occurred when ewes were given oestradiol on Days 11 and 12, or when progesterone was withdrawn on Days 11 and 12, or these two treatments were combined. Oxytocin administration caused an increase in plasma PGFM concentrations in ewes which did not receive progestagen pre-treatment, and subsequently received progesterone treatment for 5 days and oestradiol treatment on Days 4 and 5 of progesterone treatment. Similarly treated ewes which received progestagen pre-treatment did not respond to oxytocin. Oxytocin administration also increased plasma PGFM concentrations in ewes which received progestagen pre-treatment followed by progesterone treatment for 12 days, progesterone treatment for 12 days plus oestradiol on Day 11 and 12 of progesterone treatment, progesterone withdrawal on Day 11 and 12, or progesterone withdrawal and oestradiol treatment combined. The results indicate that (1) progesterone pre-treatment affects oxytocin receptor concentrations in the endometrium and uterine responsiveness to oxytocin and (2) progesterone treatment alone for 12 days after a treatment which mimics a previous luteal phase and oestrus is sufficient to induce oxytocin receptors and increase oxytocin-induced PGF release. These results emphasize the importance of progesterone and provide information which can be used to form an hypothesis for control of luteolysis and oestrous cycle length in the ewe.     

Hormonal regulation of oestrogen and progesterone receptors in cultured bovine endometrial cells.

Changes in the number of progesterone and oestradiol receptors in the endometrium are thought to play a role in the induction of luteolysis. The effect of oestradiol and progesterone on the regulation of their receptors in cultured bovine uterine epithelial and stromal cells was examined to determine the mechanisms involved in this process. Cells were obtained from cows at days 1-3 of the oestrous cycle and were cultured for 4 or 8 days in medium alone (RPMI medium + 5% (v/v) charcoal-dextran stripped newborn calf serum) or with oestradiol, progesterone or oestradiol and progesterone. At the end of culture, receptor binding was measured by saturation analysis. Specific binding of both [3H]ORG 2058 (16 alpha-ethyl-21-hydroxy-19-nor (6,7-3H) pregn-4-ene-3,20-dione) and [3H]oestradiol to epithelial and stromal cells showed high affinities (Kd = 1.1 x 10(-9) and 6 x 10(-10) mol l-1, respectively, for progesterone receptors; Kd = 5.5 x 10(-9) and 7 x 10(-10) mol l-1, respectively, for oestradiol receptors). In the stromal cells, oestradiol (0.1-10 nmol l-1) increased the number of oestradiol receptors from 0.21 +/- 0.06 to 0.70 +/- 0.058 fmol microgram-1 DNA and the number of progesterone receptors from 1.4 +/- 0.83 to 6.6 +/- 0.70 fmol microgram-1 DNA in a dose-dependent manner after 4 days of culture (P < 0.01). After culture for 8 days, the stimulatory effect of oestradiol increased. Progesterone (50 nmol l-1) had no effect on the number of oestradiol or progesterone receptors (P > 0.05). However, progesterone inhibited the stimulatory effect of oestradiol. In epithelial cells, the lower concentrations of oestradiol (0.1 and 1 nmol l-1) stimulated the number of progesterone receptors (P = 0.05) after 4 days culture, whereas the highest concentration of oestradiol (10 nmol l-1), progesterone (50 nmol l-1) and progesterone (50 nmol l-1) plus oestradiol (1 nmol l-1) had no effect. After culture for 8 days, the stimulatory effect of oestradiol decreased. In contrast to progesterone receptors, the number of oestradiol receptors increased with oestradiol concentration (P < 0.01). These data show that the number of progesterone receptors was higher in the stromal cells than in epithelial cells, whereas the number of oestradiol receptors was higher in the epithelial cells than in stromal cells. Oestradiol upregulates its own receptor and increases the number of progesterone receptors in both cell types in vitro, whereas progesterone has little effect, but inhibits the effects of oestradiol on progesterone receptors.     

Hormonal regulation of lysosomal hydrolases in the reproductive tract of the rabbit

The total protein content and the activities of lysosomal hydrolases (arylsulphatase, alkaline and acid phosphatases, beta-glucuronidase, beta-N-acetylhexosaminidase, alpha-L-fucosidase and beta-galactosidase) in the uteri of ovariectomized rabbits treated with different concentrations of progesterone, oestradiol-17 beta and a combination of progesterone and oestradiol were determined. The enzyme activities were also measured in the reproductive organs of rabbits induced to superovulate by PMSG and hCG. In superovulated and steroid-treated rabbits, the changes in lysosomal hydrolases were more obvious in the endometrium than the myometrium. Except for the myometrial alkaline phosphatase and beta-galactosidase and the endometrial alkaline phosphatase, there were no significant changes in the solubilities of hydrolases after treatment with steroids. beta-Galactosidase levels were significantly higher in the ovariectomized rabbits treated with progesterone. An antagonistic effect of oestradiol and progesterone was observed with respect to uterine weight, protein content and enzyme activities in the ovariectomized rabbits treated simultaneously with oestradiol and progesterone.     

Effects of cycloheximide on the uterine refractory state induced by 'nidatory' oestrogen in rats.

After priming with oestradiol, ovariectomized rats were given 6 days of progesterone treatment in which two doses of 50 ng oestradiol were given on Days 3 and 6. This basic treatment allows the oestradiol-induced (1st injection) disappearance of uterine sensitivity to decidual stimuli to occur. Cycloheximide could not mimic oestrogen action in the production of the uterine refractory state. However, a high dose (500 micrograms per animal) of this inhibitor given with the first injection of oestradiol allowed the uterus to remain in a neutral state and to respond to decidual induction after the second dose of oestradiol. By delaying the injection of cycloheximide after the first oestrogen treatment, protein synthesis requisite to the occurrence of uterine refractoriness would not take place within 12 h after the 'nidatory' oestrogen injection.     

雌激素在兔胚泡着床中的作用——子宫雌激素受体的研究

为了验证雌激素作用存在于完整的和去卵巢兔胚泡着床过程中,本文用~3H—雌二醇交换法测定了早期妊娠 D_3、D_5、D_7子宫组织的雌二醇受体浓度,并与去卵巢后仅补充孕酮的 D_7子宫作比较。结果显示:在 D_3、D_5、D_7的子宫细胞浆和细胞核中都存在雌二醇受体。妊娠7天去卵巢兔的子宫细胞核中雌二醇受体量与妊娠7天卵巢完整的兔作比较,二者无明显差异。这说明去卵巢后子宫细胞核中雌激素受体浓度并未受影响,因此雌激素作用依然存在。关于胚泡是否有雌激素受体的问题,本工作在胚龄5、6、7天胚泡中未测得雌二醇受体。据此,胚泡着床时,雌激素的作用可能主要通过母体子宫组织而发挥其生理效应。     

Influence of pregnancy and sex steroids on concentration, motor effect and receptor binding of VIP in the rabbit female genital tract

The influence of sex steroid and pregnancy on the tissue concentration, uterine motor effect and receptor binding of VIP has been studied in the female genital tract of pregnant rabbits and oophorectomized rabbits during progesterone and/or oestrogen substitution. The concentration of immunoreactive VIP was high in the vagina and cervix, and lower in the uterine body of both pregnant and non-pregnant rabbits. A significant decrease in the VIP concentration (pmol/g wet weight) of the uterine body was observed toward term of pregnancy. The total uterine content of VIP, however, seems unchanged. Treatment of oophorectomized rabbits with ovarian steroids had no effect on the VIP concentration. The sensitivity for and potency of VIP on the relaxation of uterine muscle was significantly higher in oophorectomized rabbits treated with a combination of progesterone and oestrogen than in control rabbits. No difference was observed between non-pregnant and pregnant rabbits. The degradation and binding affinity for 125I-labelled VIP was highest in oophorectomized rabbits substituted with both oestrogen and progesterone. In the pregnant rabbits, the amount of receptors was decreased near term. In conclusion, sex steroids are able to influence the motor effect of VIP at the receptor level, but have no effect on the VIP concentration in the female genital tract.     

Effect of ovine trophoblast protein-1, oestrogen and progesterone on oxytocin-induced phosphatidylinositol turnover in endometrium of sheep

In Exp. 1, endometrium was collected from Day-15 cyclic ewes and effects of oTP-1, oxytocin and oTP-1 + oxytocin, in various temporal relationships, on phosphatidylinositol (PI) turnover were determined. Co-treatment of endometrium with oTP-1 and oxytocin inhibited stimulatory effects of oxytocin, while treatment with oTP-1 before and during oxytocin administration had no effect. Turnover of PI was unaffected by oTP-1 alone. In Exp. 2, ovariectomized ewes were treated with progesterone (50 mg/day) for 10 days and then oestrogen (100 micrograms/day) for 2 days and endometrium was collected. Oxytocin stimulated PI turnover in endometrium, but oTP-1 had no effect alone or in combination with oxytocin. In Exp. 3, ovariectomized ewes were treated with corn oil (1 ml/day), oestrogen (50 micrograms/day), progesterone (50 mg/day) or progesterone + oestrogen for 10 days and endometrium was collected. Oxytocin stimulated PI turnover only in ewes that received progesterone. oTP-1 alone had no effect on PI turnover, while co-treatment of endometrium with oxytocin and oTP-1 stimulated PI turnover in ewes treated with progesterone, but not progesterone and oestrogen. Pretreatment of endometrium with oTP-1 stimulated PI turnover when ewes were treated with progesterone or progesterone + oestrogen. Pretreatment of endometrium with oxytocin and then treatment with oTP-1 inhibited PI turnover compared to treatment with oxytocin alone. In Exp. 4, ovariectomized ewes were treated as in Exp. 2. Catheters were placed into the uterine horns and ewes received oTP-1 into one horn and serum into the other twice daily on Days 10-12 of steroid treatment. Endometrium collected on Day 13 was used to measure PI turnover and received either no treatment or oxytocin. Oxytocin stimulated PI turnover in endometrium of these ewes and in-vivo treatment of the ewes with oTP-1 had no effect on PI turnover. These results indicate that antiluteolytic effects of oTP-1 are not mediated by inhibiting effects of oxytocin on phosphatidylinositol turnover if oxytocin receptors are present and that uterine responsiveness to oxytocin is progesterone dependent.     

Progesterone receptors and ventilatory stimulation by progestin

Progestin is thought to be a ventilatory stimulant but its effectiveness in raising ventilation is variable in humans and other species. We hypothesized that the level of progesterone receptors was an important determinant of the ventilatory response to progestin. Since estradiol induces progesterone receptor formation, we compared the ventilatory effect of the synthetic progestin medroxyprogesterone acetate (MPA) given in combination with estradiol with the effects of estradiol alone, MPA alone, or vehicle (saline) in ovariectomized rats. Animals receiving MPA alone had low numbers of progesterone receptors (2.43 pmol/g uterine wt) and had no change in ventilation, arterial Pco2, or Po2. MPA administration raised ventilation 23 +/- 5%, lowered arterial Pco2 3.2 +/- 0.9 Torr (both P less than 0.01) and tended to raise arterial Po2 when given in combination with estradiol to animals with increased numbers of progesterone receptors (4.85 pmol/g uterine wt). Estradiol alone produced the highest number of progesterone receptors (12.3 pmol/g uterine wt) but had no effect on ventilation or arterial Pco2 and decreased arterial Po2. Combined estradiol plus MPA treatment produced a greater fall in arterial Pco2 than did treatment with MPA alone, estradiol, or saline (all P less than 0.05). These results suggest that both an elevation in progestin levels and progesterone receptor numbers are required to stimulate ventilation.     

Effects of human chorionic gonadotrophin on contractile activity of steroid-primed pig myometrium in vitro

We examined the effects of (a) oestrogen and progesterone on concentrations of luteinizing hormone/human chorionic gonadotrophin (LH/hCG) receptors in uterine smooth muscle in vivo and (b) hCG on spontaneous myometrial contractions in vitro. Ovariectomized gilts received 2 ml corn oil (control; n = 5), 2 mg oestradiol benzoate (n = 6) or 20 mg progesterone (n = 5) for 5 days. Gilts were hysterectomized 8 h after the last injection and longitudinal sections of myometrium were incubated in modified Krebs' solution with 0 or 10 i.u. of hCG (n = 10/gilt) for 4 h at 37 degrees C in 95% O2:5% CO2. After incubation, myometrial sections were placed in a tissue chamber perfused with Krebs' solution and mechanical activity was recorded for 30 min. Cell membrane fractions were prepared from myometrial tissue not used for in-vitro studies and analysed for LH/hCG receptors. Treatment with oestradiol benzoate increased (P less than 0.01) the number of LH/hCG-binding sites compared with gilts receiving corn oil or progesterone. Incubation of myometrium with hCG reduced (P less than 0.01) the frequency and amplitude of spontaneous uterine contractions in gilts treated with oestradiol benzoate. In contrast, hCG had no effect (P greater than 0.05) on the pattern of myometrial contractions in gilts given corn oil or progesterone. These results indicate that oestradiol promotes the synthesis of LH/hCG receptors in pig myometrium and incubation of oestrogen-primed tissue with hCG has a quiescent effect on myometrial contractility.