4-day Cyclic Rats Research Articles

Effects of ovarian dopaminergic receptors on ovulation.

Hormonal and neural signals regulate the ovarian follicular development. The present study's hypothesis is that the blockade of ovarian dopamine receptors locally will affect follicle development and ovulation. Groups of adult 4-day cyclic rats of the CII-ZV strain on estrus, diestrus-1, diestrus-2, or proestrus day were injected with vehicle, haloperidol (DA2 > DA1 blocker), sulpiride (DA2 blocker), or SCH-23390 (DA1 blocker) into the bursa of both ovaries at 08:00, 13:00, or 20:00 h. Animals were sacrificed the following predicted estrus day. The following treatments blocked ovulation: injecting haloperidol to rats on estrus or diestrus-1 at 8:00, 13:00, or 20:00 h and to rats on diestrus-2 at 08:00, or 20:00 h; injecting SCH-23390 to rats on diestrus-1 at 8:00, 13:00, or 20:00 h; injecting sulpiride to rats on estrus at 20:00 h, diestrus-1 at 08:00, 13:00, or 20:00 h and to rats on diestrus-2 at 08:00 h. In rats treated with any of the dopamine antagonists that blocked ovulation, injecting GnRH at 14.00 h on the next predicted proestrus day restored ovulation. Injecting estradiol benzoate at 14.00 h of the next predicted diestrus-2 restored ovulation in some animals treated with haloperidol on estrus or diestrus-2 and was ineffective in rats treated on diestrus-1. In rats treated with sulpiride or SCH-23390 ovulation occurred in most animals (SCH-23390: 6/8; SPD: 9/12). Present results suggest that dopamine ovarian receptors' participation in regulating follicular development and ovulation varies along the estrus cycle, with their most prominent activity occurring on diestrus-1.

Effects of cottonseed oil (Gossypium Spp.) and cottonseed meal on estrous cycle, ovulation and histoarchitecture of female reproductive organs of adult cyclic Sprague-Dawley rats

Experiments were conducted to determine the effects of various forms of cottonseed oil (whole Cottonseed, “Refined” industrially extracted Cottonseed oil and “Crude” locally extracted Cottonseed oil) on the Estrous cycle and Ovulation, and Histoarchitecture of female reproductive organs. Regular 4-day adult cyclic female Sprague-Dawley rats were divided into four groups; three experimental and one control of five rats each. Group A rats were fed with 1.5mls/kg body weight of industrially extracted “refined” cottonseed oil-Sunola ® . Group B with 2mls/kg body weight of finely grounded whole cottonseed powder, while same number of animals in group C were fed with locally extracted “crude” cottonseed oil. Daily Vaginal smears were taken between 8-9am. Six estrous cycles were monitored before administration of the test substances, another six cycles were monitored during the periods the test substances were administered, then another six cycles were studied after withdrawal of the test substances. Effects of the test substances on ovulation were also studied by administering the test substances on the morning of proestrous and counting the number of ova shed on estrous. Adrenal glands and reproductive organs of test and control animals were subjected to histological study. Varying degrees of variation from the expected 2:1:1 ratio of number of diestrous: proestrous: estrous days were noticed. The variation was greatest in group B animals which were treated with finely ground whole cottonseed powder. Ovulation was completely blocked in animals treated with locally extracted “crude” cottonseed oil (Group C). Histological studies of reproductive organs of control and experimental animals showed normal histology. Keywords : cottonseed oil, cottonseed meal, estrous cycle, ovulation Nigerian Journal of Health and Biomedical Sciences Vol. 5(1) 2006: 21-26

Tamoxifen but Not Other Selective Estrogen Receptor Modulators Antagonizes Estrogen Actions on Luteinizing Hormone Secretion while Inducing Gonadotropin-Releasing Hormone Self-Priming in the Rat

Selective estrogen receptor modulators (SERMs) are compounds which may function as agonists or antagonists depending upon the target tissue. This study compares the actions of different SERMs on luteinizing hormone (LH) secretion, and on gonadotropin-releasing hormone (GnRH) self-priming in the rat. To do this, 4-day cyclic rats were injected twice, on day 2 (metestrus) and day 3 of the estrous cycle, with one of the following SERMs: 0.25 mg ICI 182,780, 3 mg tamoxifen (TX), LY139481-HCl or LY117018-HCl, or 0.5 mg RU58668. Control rats were given subcutaneous injections of 0.2 ml oil. On the morning of day 4 (proestrus in controls), rats from each group were either injected intraperitoneally with pentobarbital (40 mg/kg) for in vivo study or decapitated and their pituitaries collected for incubation (in vitro study). Additionally, pituitaries taken on each day of the estrous cycle from control rats as well as on day 4 from SERM-treated rats were processed for immunohistochemical determination of the estrogen receptor-α (ERα) gonadotrope. The plasma concentration or accumulation of LH in the medium was determined after 1 h (basal secretion). Thereafter, an intravenous bolus of GnRH (50 ng/0.5 ml/100 g BW) or 10^–8M GnRH was injected or added to the medium, respectively. After 1 h of GnRH exposure, blood or medium were taken, and another challenge of GnRH was made. At the end of the 3rd h of the experiment, blood or medium samples were taken again and the LH plasma concentration or accumulation in the medium were determined. All SERM treatments reduced uterus weight and decreased basal and stimulated LH secretion. Also, on day 4, rats treated with any SERM other than TX showed vaginal smears infiltrated by leukocytes and a reduction in GnRH self-priming. TX-treated rats exhibited cornified vaginal smears and an estrogenic effect on GnRH self-priming. Moreover, 15-min exposure to two consecutive GnRH (10^–8M) challenges 1 h apart in incubated pituitaries with estradiol (E₂, 10^–8M), TX (10^–7M), E₂ + TX, or medium alone form ovariectomized rats injected for 3 days with estradiol benzoate (25 µg), TX (3 mg), estradiol benzoate + TX, or 0.2 ml oil, respectively, showed that TX increased GnRH self-priming, as did E₂, whereas it reduced the E₂-sensitizing effect on GnRH-stimulated LH secretion and cancelled the E₂-dependent GnRH self-priming. All SERMs prevented the physiological nucleocytoplasmic shuttling of ERα exhibited during proestrus in control rats, and TX, in addition, induced a significantly larger number of gonadotropes displaying strong cytosolic immunosignals corresponding to ERα than the rest of the experimental groups. Overall, data from this study indicated that, in contrast to the general antagonistic effect of the tested SERMs, TX seemed to display both selective agonist and antagonist activity at the gonadotrope level and on GnRH self-priming of LH secretion respectively.

The in vitro inhibitory action of antiprogestin RU486 on LH and FSH secretion in the absence of progesterone in rats is estrogen-dependent.

Previous in vivo findings show that in the virtual absence of progesterone (P), the antiprogestin RU486 reduces LH and FSH secretion in proestrous rats, indicating that activation of P receptor (PR) can occur in the absence of the cognate ligand. The present study investigates, in vitro, whether or not the inhibitory effect of antiprogestin RU486 on gonadotropin secretion in the absence of P is estrous cycle dependent, and whether its specific expression in proestrus mirrors the high estrogen (E2) background. In the first experiment we investigated the effect of RU486 (10 nM) and/or LHRH (10 nM) on LH and FSH secretion in incubated pituitaries collected on each day of the estrous cycle of the rat. In the second experiment, we determined the effect of RU486 and/or LHRH on preovulatory LH and FSH release by pituitaries from female rats that were ovariectomized (OVX), treated with the antiestrogen LY117018-HCL (Eli Lilly & Co.), or injected with 20 micrograms of estradiol benzoate (EB). The third experiment investigated the effect of RU486 and/or LHRH on LH and FSH release by pituitaries collected from intact or EB-treated (0.1 mg/kg over three consecutive days) male rats. RU486 reduced both basal and LHRH-stimulated LH and FSH secretion in proestrous pituitaries from normal 4-day cyclic rats. By contrast, in diestrous pituitaries, RU486 increased both parameters of LH secretion but was without effect on FSH release. RU486 was also without effect in pituitaries collected from rats in estrus or metestrus, or from OVX or antiestrogen-treated rats. Moreover, EB injection or treatment induced the full inhibitory effect of RU486 in pituitaries from female and male rats, respectively. The above results suggested that P occupancy of the receptor is not required for the formation or function of the active receptor and hence for preovulatory LH and FSH secretion, and that this form of PR activation at pituitary level is E2-dependent and not genetically determined.

Effects of progesterone on the secondary surge of follicle-stimulating hormone in the rat.

In the cyclic rat, the secondary surge of FSH on estrus appears to depend on the LH surge-induced fall in serum concentrations of inhibin. To investigate the involvement of progesterone in the regulation of the secondary surge of FSH, 4-day cyclic rats were treated on proestrus with an antagonist of LHRH (LHRHant) and with an ovulatory dose of ovine (o) LH, progesterone, the antiprogestin RU486, or the combination of RU486 and oLH. Serum concentrations of gonadotropins and inhibin at 1830 h on proestrus and at 0030 h on estrus were determined, and the expression of inhibin/activin subunit mRNAs in the ovary at 0030 h on estrus was analyzed by in situ hybridization. Rats receiving saline showed low expression of alpha-, beta(A)-, and beta(B)-subunit mRNAs in the ovary and low serum levels of inhibin in conjunction with the elevated serum concentrations of FSH on estrus. Administration of LHRHant blocked the decrease in the synthesis and secretion of inhibin and abolished the FSH secondary surge, whereas the injection of oLH prevented these effects. Exogenous progesterone, compared with LHRHant injection, increased alpha-, beta(A)-, and beta(B)-subunit mRNA hybridization intensity in the ovary and serum inhibin immunoreactivity, and also restored, in part, the surge of FSH on estrus. The antiprogestin RU486 did not modify the effect of oLH on either inhibin/ activin subunit mRNAs in the ovary or serum levels of inhibin, but blocked the FSH surge. These results indicate that, in the cyclic rat, 1) the secretion of progesterone on proestrous afternoon, induced by the LH surge, is not involved in the fall of ovarian inhibin synthesis and secretion; and 2) in combination with a drop in serum inhibin, a stimulatory action of progesterone on another factor, possibly pituitary activin, could be necessary to elicit a complete secondary surge of FSH.

Characterization of the Atrial Natriuretic Peptide System in the Oviduct

The atrial natriuretic peptide (ANP) gene is expressed in several extraatrial tissues in which ANP may be involved in the regulation of autocrine or paracrine functions. In the ovary, the synthesis of ANP, its binding sites, and a physiological role were found. The ANP system in the oviduct, however, is yet to be defined. The purpose of the present study was to determine whether the ANP system is present in the oviduct and then to define its function. The serial dilution curves of oviductal extracts in rat and rabbit were parallel to the standard curve of ANP. Molecular profiles using reverse phase HPLC indicated that the prohormone and processed circulating peptide were the main forms present. The immunoreactive ANP content of the oviduct was 27.07 ± 4.41 pg/mg tissue wet wt (1.19 ± 0.19 ng/oviduct; n = 10; at metestrus) in rats and 1.21 ± 0.12 pg/mg tissue wet wt (0.15 ± 0.01 ng/oviduct; n = 12) in rabbits. In adult 4-day cycling rats, the immunoreactive ANP contents in oviducts had a cyclic change characterized by the lowest level at proestrus (14.59 ± 3.24 pg/mg; n = 12). A distinct and strong ANP immunoreactivity was found in the mucosal layer of rat oviduct, and ANP messenger RNA was also detected in the oviduct by reverse transcriptase-PCR. Specific high affinity binding sites for iodinated rat ANP ([125I]rANP) were observed in the mucosal layer of the oviduct in rats and rabbits. Specific [125I]rANP bindings localized in the mucosal layer of rabbit oviduct showed an apparent dissociation constant (Kd) of 18.69± 5.55 nm and a maximal binding capacity of 14.85 ± 6.19 fmol/mm2. These specific [125I]rANP bindings were not reversed by des-[Gln18,Ser19,Gly20,Leu21,Gly22]ANP-(4–23) as a selective ligand of clearance receptor. Synthetic ANP inhibited both the frequency and amplitude of basal motility of rabbit oviduct in a dose-dependent manner. These results suggest that the oviduct has its own ANP system, and the system is involved in the regulation of oviductal motility.

Characterization of the atrial natriuretic peptide system in the oviduct.

The atrial natriuretic peptide (ANP) gene is expressed in several extraatrial tissues in which ANP may be involved in the regulation of autocrine or paracrine functions. In the ovary, the synthesis of ANP, its binding sites, and a physiological role were found. The ANP system in the oviduct, however, is yet to be defined. The purpose of the present study was to determine whether the ANP system is present in the oviduct and then to define its function. The serial dilution curves of oviductal extracts in rat and rabbit were parallel to the standard curve of ANP. Molecular profiles using reverse phase HPLC indicated that the prohormone and processed circulating peptide were the main forms present. The immunoreactive ANP content of the oviduct was 27.07 +/- 4.41 pg/mg tissue wet wt (1.19 +/- 0.19 ng/oviduct; n = 10; at metestrus) in rats and 1.21 +/- 0.12 pg/mg tissue wet wt (0.15 +/- 0.01 ng/oviduct; n 12) in rabbits. In adult 4-day cycling rats, the immunoreactive ANP contents in oviducts had a cyclic change characterized by the lowest level at proestrus (14.59 +/- 3.24 pg/mg; n = 12). A distinct and strong ANP immunoreactivity was found in the mucosal layer of rat oviduct, and ANP messenger RNA was also detected in the oviduct by reverse transcriptase-PCR. Specific high affinity binding sites for iodinated rat ANP ([125I]rANP) were observed in the mucosal layer of the oviduct in rats and rabbits. Specific [125I]rANP bindings localized in the mucosal layer of rabbit oviduct showed an apparent dissociation constant (Kd) of 18.69 +/- 5.55 nM and a maximal binding capacity of 14.85 +/- 6.19 fmol/mm2. These specific [125I]rANP bindings were not reversed by des-[Gln18,Ser19,Gly20,Leu21,Gly22]ANP-(4- 23) as a selective ligand of clearance receptor. Synthetic ANP inhibited both the frequency and amplitude of basal motility of rabbit oviduct in a dose-dependent manner. These results suggest that the oviduct has its own ANP system, and the system is involved in the regulation of oviductal motility.

Follicular and Luteal Progesterone Play Different Roles Synchronizing Pituitary and Ovarian Events in the 4-Day Cyclic Rat1

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

Effect of lactation on hypothalamic preproenkephalin gene expression.

Enkephalin appears to modulate several aspects of reproductive function in female rats. The purpose of this study was to determine if lactation influences preproenkephalin gene expression in one or more hypothalamic nuclei known to be involved in maternal or reproductive behavior and prolactin secretion. Lactating rats were killed on day 3 (LAC 3) or day 10 (LAC 10) of lactation. Controls consisted of regular 4-day cycling rats that were killed on diestrous day 1, with 9 to 12 females per group. We used in situ hybridization histochemistry to assess preproenkephalin gene expression in individual cells in the medial preoptic nucleus, anterior, medial and posterior arcuate nucleus, magnocellular and parvocellular aspects of paraventricular nucleus, and ventromedial nucleus. Preproenkephalin mRNA in the anterior arcuate nucleus increased to reach significance (P < 0.05) at day 10 of lactation. Levels in the medial arcuate nucleus increased significantly (P < 0.001) by day 3 of lactation (LAC 3) and remained elevated on day 10 (LAC 10). No significant differences between lactating and control rats were detected in preproenkephalin mRNA levels in the posterior arcuate nucleus, medial preoptic nucleus or in the ventromedial nucleus. Substantial levels of preproenkephalin mRNA were found in the paraventricular nucleus, particularly in a limited region of the magnocellular portion. However, these levels did not change with lactation. These data provide evidence for differential regulation of the preproenkephalin gene during lactation. This change may contribute to lactational hyperprolactinemia and suppressed GnRH secretion, leading to reproductive acyclicity.

Recombinant FSH (Org32489) induces follicle growth and ovulation in the adult cyclic rat.

The effects of a single injection of recombinant human FSH (rhFSH; Org32489) on ovulation rate and timing and on antral follicle growth were studied in adult 5-day cyclic rats. Rats injected at 1700 h on dioestrus-2 with a dose of 10 IU rhFSH showed, on average, no increase in ovulation rate on the day of expected oestrus. However, an additional, precocious ovulation resulting in a normal number of corpora lutea (13.3 +/- 0.4, n = 6) was found to take place on the night after injection, i.e. dioestrus-3. No mating behaviour, as shown by the absence of vaginal plugs the next morning, was observed at this ovulation. Follicle counts showed a loss of large antral follicles due to ovulation and increased numbers of healthy small antral follicles at 17 and 41 h after injection, indicating a decrease of atresia of growing follicles as well as additional recruitment of new antral follicles. The endogenous serum FSH concentration on the subsequent day of oestrus (65 h after the rhFSH injection) as well as recruitment of small antral follicles were lower in the rhFSH-treated rats than in saline-treated controls. The ovulation at oestrus, 48 h after the precocious, rhFSH-induced ovulation showed large differences in the number of oocytes between the rats in one treatment group. Similar results in terms of immediate ovulation induction were obtained by using a highly purified human urinary FSH preparation (i.e. metrodin). Furthermore, the direct induction of ovulation by rhFSH or metrodin could not be prevented by the injection of an LHRH antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Inappropriate ovarian feedback in basal gonadotropin secretion in 4-day cyclic rat treated with mifepristone: Role of endogenous estradiol

Administration of the antiprogesterone RU486 to 4-day cyclic rats from metestrus onwards resulted in a dissociation of basal LH and FSH secretion and ovariectomy abolished this effect of RU486. Since RU486 also induces abnormally high concentrations of testosterone without affecting estradiol concentrations during the diestrous phase, we have studied the involvement of androgen or estrogen in RU486-dissociated gonadotropin secretions. Ovariectomized- (OVX) or sham-OVX rats at 08:00 h in metestrus were injected with RU486 (2 mg) or vehicle (0.2 ml) at 08:00 and 17:00 h in metestrus (day 1) and diestrus (day 2). Also, OVX-and sham-OVX rats injected with RU486 or oil were, in addition, treated with the antiandrogen flutamide and/or the antiestrogen tamoxifen (1 mg/0.2 ml) at 08:00 and 17:00 on days 1 and 2. The serum concentrations of LH and FSH were determined at 08:00 and 17:00 h on days 1 and 2 and at 08:00 h on day 3. OVX completely reversed the effects of RU486 on basal gonadotropin secretions while flutamide treatment affected neither LH nor FSH in any of the groups studied. On the contrary, tamoxifen treatment in RU486-injected rats reduced the LH concentrations to the levels found in OVX-rats and increased FSH concentrations to the levels in sham-OVX rats. Since the doses of flutamide and tamoxifen used block the action of androgens and estrogens, respectively, the results of this study evidence that endogenous estradiol in the absence of the effects of progesterone at both hypothalamus-pituitary and ovary levels stimulates LH and inhibits FSH secretion during the low secretion rate of gonadotropins in the rat.

Evaluation of biological activity of LHRH antagonists by three methods

We have previously screened the LHRH antagonists synthesized by our institute using the method of antiovulatory activity in the 4-day cycling rat(l,2). In this study we evaluated the biological activity of several new LHRH antagonists synthesized by our institute using three new methods: a. Suppression of ovulation in the cycling rat(3); b. Inhibition of ovulation in the pregnant mare’s serum gonadotropin (PMSG) treated immature rat(4); c. Inhibition of LH secretion in the adult ovariectomized rat.

Effect of chloroquine on oestrus cycle and ovulation in cyclic rats

We conducted experiments to determine the effects of chloroquine (CQ) on the oestrus cycle and ovulation in 4-day cyclic rats. There were two treatment groups. Group I animals had chloroquine phosphate (40 mg kg-1 body wt.) administered intraperitoneally (i.p.) starting from dioestrus day 1, once a day, 5 days a week for 4 weeks. Oestrus smear was monitored by daily saline vaginal lavage. Control rats received an equal volume of physiological saline. All animals were sacrificed at the end of the 4th week of treatment. Group II animals also received chloroquine phosphate (40 mg kg-1 body wt.) administered in a single dose at either 0900 h or 1800 h pro-oestrus, and on the morning of oestrus the rats were killed. Trunk blood was collected in each group at the time of sacrifice, centrifuged and the serum stored for subsequent radioimmunoassay of luteinizing hormone (LH), follicle stimulating hormone (FSH) and oestrogen. The fallopian tube was dissected out and a search made for the ova. Results showed that administration of chloroquine altered the oestrus cycle (i.e. the rats showed a persistent dioestrus smear), lowered serum oestrogen and luteinizing hormone levels while serum FSH was unaltered, prevented the expected ovulation when injected at 0900 h pro-oestrus and did not affect ovulation in rats injected at 1800 h pro-oestrus. This study supports the notion that chloroquine has an adverse effect on hypothalamo-pituitary ovarian systems.

Different effects of the antiprogesterone RU486 on progesterone secretion by the corpus luteum of rats with 4- and 5-day oestrous cycles

Administration of the antiprogesterone RU486 (2 mg/day) for 14 days to rats with a 5-day reproductive cycle resulted in an increase in both ovarian and pituitary weight in contrast with rats with a 4-day oestrous cycle. Luteal progesterone production decreased earlier in 4-day than in 5-day cyclic rats. Treatment of 5-day cyclic rats with antiprogesterone from the day of metoestrus onwards resulted in the advancement of the preovulatory prolactin surge by 24 h. Progesterone production by the corpus luteum was, however, not affected, indicating that in 5-day cyclic rats the corpora lutea are still functionally active at the time of the preovulatory surge of prolactin. They become, therefore, stimulated both in size and progesterone production. In contrast, the corpora lutea in 4-day cyclic rats are functionally inactive at the time of the preovulatory surge of prolactin, and prolactin acts luteolytically. In conclusion, the advancement of the preovulatory surge of prolactin by 24 h accounts, at least in part, for the increase in ovarian weight in 5-day cyclic rats after treatment with antiprogesterone. The results of these experiments do not agree with a direct effect of the antiprogesterone RU486 on progesterone secretion by the corpus luteum.

Ovarian atrial natriuretic peptide during the rat estrous cycle

The changes in ovarian levels of immunoreactive atrial natriuretic peptide (irANP) and arginine vasopressin (irAVP) were observed during the estrous cycle of rat. We also demonstrated the synthesis of ovarian ANP. In adult 4-day cycling rats, ovarian level of irANP was found to be the highest on proestrus and was to be the lowest on diestrus. Ovarian irANP level inversely correlated with ovarian level of irAVP. On reverse-phase HPLC, two distinct peaks of ovarian irANP, high and low molecular weight forms, existed in the each stage of the estrous cycle. However, no significant changes in plasma and atrial concentrations of ANP were observed during the cycle. The rat ovary contained mRNA coding for ANP. These data showing the synchronized cyclic change of ovarian irANP and irAVP with the estrous cycle suggest that the ovary locally synthesizes ANP and ovarian ANP may play regulatory roles on the follicular fluid dynamics.

Hormone concentrations and ovulatory response in rats treated with antiprogestagens

Administration of antiprogestagens (2 mg/day) to female rats for 21 days induces high serum prolactin levels. These levels stimulate luteal progesterone production and an increase in ovarian weight. Compared with RU486 (mifepristone) the increase in prolactin is less after treatment with ZK299 (onapristone), an antiprogestagen with lower antiglucocorticoid activity. To study whether cyclic ovulations occur in rats treated with antiprogestagens, 5-day cyclic rats were given daily injections of RU486 or ZK299 (2 mg) from metoestrus (day 1) to pro-oestrus. This treatment advanced the forthcoming ovulation by 1 day; however, the ovulation rate was low. Injection of 10 IU human chorionic gonadotrophin on the afternoon of pro-oestrus (day 3) increased the ovulation rate, but not to the level found in oil-treated rats. Serum LH concentrations measured from metoestrus to oestrus at 10.00 and 17.00 h were higher in antiprogestagen- than in oil-treated rats from day 2 (17.00 h) onwards. A low preovulatory LH surge was found in antiprogestagen-treated rats on the afternoon of pro-oestrus (day 3). Ovarian histology at the day of oestrus (day 4) confirmed the presence of a low LH surge as, besides ruptured follicles, unruptured follicles with dispersion of cumulus cells were present. The pro-oestrus surge of prolactin was also advanced by 24 h. The magnitude, however, was not different from that in oil-treated rats at day 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypersecretion of Follicle-Stimulating Hormone (FSH) after Ovariectomy of Hypophysectomized, Pituitary-Grafted Rats: Implications for Local Regulatory Control of FSH*

Previous observations have shown that a portion of the acute (less than 12 h) FSH hypersecretion after ovariectomy (OVX) is LHRH independent, thereby suggesting that mechanisms governing the acute FSH hypersecretory response to OVX may reside largely within the anterior pituitary gland. Accordingly, the present studies were conducted to determine whether acute OVX-induced FSH hypersecretion can be elicited in an animal model in which the anterior pituitary gland is isolated from diencephalic chemical signals, and if so, whether the hypersecretion could be abated by the FSH-suppressing protein, follistatin. Adult female rats hypophysectomized (H) 1 week earlier received anterior pituitary grafts (H/G) (one to three glands per rat) under the kidney capsule. In order to increase ovarian secretion of negative feedback effectors substances (i.e. estrogen, inhibin), some H/G rats were injected sc with 30 IU PMSG 4-6 days after receiving pituitary transplants, whereas other rats were given the saline vehicle. Two days later (0830 h), a blood sample was obtained via an indwelling atrial catheter inserted the previous day. H/G rats given saline or PMSG then were further subdivided and either castrated or sham castrated. Additional blood samples were obtained from the catheter, and trunk blood was collected from decapitated rats 24 h after OVX for measurement of serum estradiol and PRL levels. For comparison, H rats not receiving renal pituitary transplants were subdivided into similar experimental groups as the H/G rats. Blood samples were also obtained after sham OVX or OVX of pituitary-intact, 4-day cycling rats on diestrous day 1. Ovariectomy of PMSG-treated H rats receiving either one or three pituitary allografts resulted in a significant (P less than 0.01) increase in serum FSH levels by 12 h after OVX followed by a 2- to 3-fold increase in FSH levels by 24 h relative to either the pre-OVX FSH levels measured in this group or the FSH levels measured in PMSG-treated H/G rats 24 h after sham OVX. In contrast, OVX of saline-treated H/G rats failed to elicit FSH hypersecretion. Similarly, FSH hypersecretion was not observed after OVX of saline- or PMSG-treated H rats. Whereas serum LH levels were increased 24 h after OVX of diestrous rats, no such increases were detected 24 h after OVX of any H or H/G rats. In an additional experiment, H rats receiving two pituitary allografts were treated with PMSG and subsequently castrated. Twenty-four hours later, rats were injected iv with either 60 micrograms purified porcine follistatin or saline.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of Antiestrogens on Ovarian Aldo-Keto Reductase in Relation to Ovulation in Rats.

The pharmacological effects of antiestrogens on ovarian aldo-keto reductase and ovulation were investigated in rats. The activities of reduction of 13,14-dihydro-15-keto-PGF2 alpha, 4-benzoylpyridine and menadione in ovarian cytosol were significantly decreased by antiestrogen treatments, and the ovulation was completely inhibited. However, administration of luteinizing hormone-releasing hormone at 3:00 p.m. on the day of proestrus restored both enzyme activities and ovulation, which were inhibited by antiestrogens, to control levels. These results indicate that nonsteroidal antiestrogen inhibits the luteinizing hormone surge on the day of proestrus in 4-day cycling rats and that ovarian aldo-keto reductase may be closely involved in the ovulatory process in rats.

Effect of Human Growth Hormone on the Reproduction of Female Rats

Female rats were treated with human growth hormone (hGH) 0.3, 1.0 and 3.3 IU/kg daily for two weeks before mating, throughout mating and during the first seven days of pregnancy. Treatment with 1.0 and 3.3 IU/kg hGH caused a significant prolongation of the oestrous cycle. As a consequence the number of mating days was more than doubled compared to placebo treatment. The number of implantation sites and corpora lutea was significantly higher in hGH treated rats than in placebo treated rats. The number of early resorptions was increased in the rats given 3.3 IU/kg. The number of foetuses in rats sacrificed on day 20 of pregnancy and the number of viable offspring from the rats allowed to give birth were significantly increased by treatment with 1.0 IU/kg hGH. In a study of 4-day cyclic rats, treatment with 3.3 IU/kg hGH caused a prolongation of the cycle length to an average of 10.1 days, and the plasma progesterone levels tended to be higher in those rats in which the cyclic patterns had been most deranged. Foetal body weights were increased in the hGH groups, and a study with 125I-hGH indicated that hGH administered to pregnant rats will to some extent pass the placenta.

Evidence that desensitization of the negative feedback of oestrogen and priming for the positive feedback of oestrogen depend upon a common mechanism of oestrogen action in rats

Oestrogen priming of the central nervous system is required for the positive feedback of oestrogen, and the sensitivity of the negative feedback of oestrogen can be reduced by oestrogen itself. Using adult female and male rats we examined the possibility that these effects depend upon a common mechanism of oestrogen action that is mediated by the medial preoptic area (MPOA). Guide cannulae were implanted in the MPOA of 4-day cyclic rats which were ovariectomized during the evening of day 1 of dioestrus. Glass capillary tubes containing different substances were placed in the cannulae between 09.00 and 12.00 h on the presumptive day 2 of dioestrus. The effectiveness of oestrogen priming was evaluated by examining whether an s.c. implant of oestradiol-17 beta (OE2) induced an LH surge, and the inhibitory effect of oestrogen on tonic LH secretion was investigated by injecting the rats with 3 micrograms oestradiol benzoate (OB)/100 g body weight. The priming effect of an s.c. implant of OE2 could be imitated by the bilateral implantation in the MPOA of a mixture of OB and cholesterol at a ratio of 1:360 for 3 h only. Similar medial preoptic oestrogen implantation also significantly reduced the LH-inhibiting effect of OB. In accord with findings obtained in former studies on desensitization of the negative oestrogen feedback, oestrogen priming resulting from the s.c. administration of OE2 could be suppressed by short-term medial preoptic implantation of clomiphene citrate or apomorphine; bilateral electrical stimulation of the medial amygdaloid nucleus induced an increase in the serum concentration of LH in ovariectomized females implanted with OB in the MPOA, but not in castrated males pretreated and implanted with OB.(ABSTRACT TRUNCATED AT 250 WORDS)