Inhibition of the first ovulation and ovarian prostaglandin F2 alpha metabolism by danazol in rats.

The present study was conducted to investigate the mode of action of danazol by monitoring the first ovulation, serum luteinizing hormone (LH) levels and ovarian prostaglandin (PG) F2 alpha metabolism in pregnant mare serum gonadotropin (PMSG)-primed immature female rats. When danazol (750 mg/kg) was given p.o. once a day for 5 days (day 24-28), the occurrence of the first ovulation, the increase in capacity to form 13,14-dihydro-PGF2 alpha and PGF2 alpha levels induced by PMSG (5 IU) injected on day 26 were clearly inhibited on day 29. Danazol also markedly suppressed the LH surge occurring on day 28. Although the danazol-induced blockage of ovulation was restored by injection of human chorionic gonadotropin, the number of oocytes was significantly decreased as compared with that of controls. The present data indicate that the inhibitory actions of danazol on ovulation and ovarian PGF2 alpha metabolism may occur via some direct effects on the ovary in addition to the suppression of gonadotropin release from the pituitary gland.     

Effects of Tylosin on the Pituitary-Gonadal Axis in Male Rats

Abstract: Former investigations in rats showed a decrease of thyroid hormone concentrations after treatment with the antibiotic and growth promoter tylosin (Schäfer 1984). In the present study, the effects of tylosin on the pituitary-gonadal axis in adult rats were studied. The substance was administered in two concentrations to rats (0.1 and 5.0 mg tylosin/kg feed) for three different periods: 15, 29 and 65 days. At the end of each period the organ weights were determined and the hormone levels in serum and pituitary gland were measured by radioimmunoassay. After 15 days reduced levels of LH (luteinizing hormone) and FSH (follicle stimulating hormone) in the pituitary gland and LH in serum were found. Moreover, the weight of seminal vesicles was decreased and the weight of pituitary increased. After 29 days an equilibrium between effects of tylosin and endocrine contraregulation seemed to be achieved. The prolonged tylosin administration (65 days) depressed testosterone concentration and increased hypophyseal LH stores. The testing of the pituitary-testicular axis with acute LHRH (luteinizing hormone-releasing hormone) stimulation caused a reduced increse of LH in animals treated with 0.1 mg tylosin. In contrast, the LH responsiveness to LHRH in animals treated with 5.0 mg tylosin was unchanged, while the testosterone response to released LH was reduced. These findings demonstrate that tylosin acts on the pituitary as well as on peripheral functions of the pituitary-gonadal-axis and that its effect depends on the time interval of tylosin administration.     

The effects of morphine sulphate on ovulation in the immature rat treated with PMSG

Two experiments were carried out on the effects on ovulation of morphine sulfate administered prior to the preovulatory LH surge in the immature rat treated with PMSG. At the commencement of the experiments, rats were 30 days old. In Experiment 1 all rats were injected subcutaneously with 12 IU of PMSG at 1200 hr on day 30. Doses of 6, 12, 24 and 36 mg/kg of morphine were given IP at 1555 hr on day 32. Examination of oviducts on the morning of day 33 enabled the verification of ovulation as well as oocyte counts. Results suggest that the effect of morphine on ovulation is biphasic resulting in the stimulation of ovulation at low doses (6 mg/kg) and inhibition of ovulation at high doses (24 and 36 mg/kg). In Experiment 2, rats injected with a low dose of PMSG sufficient to result in ovarian maturation but not in a preovulatory LH surge, were injected on the eve of day 32 with either saline, 6 or 24 mg/kg morphine. The treatment of rats with 6 mg/kg morphine significantly increased mean ovulatory values compared with control and 24 mg/kg morphine conditions. Further, the percentage of 6 mg/kg treated rats ovulating was more than that of both control and 24 mg/kg morphine conditions. The failure of rats treated with 24 mg/kg morphine to display increments in ovulatory response similar to 6 mg/kg morphine injected rats suggests that increased ovulation is not due to the ability of morphine to cause adrenal progesterone release but is more probably the result of LH release at low doses of morphine.     

Alterations in hypothalamic and pituitary hormone levels induced by neonatal treatment of female mice with diethylstilbestrol.

Neonatal female mice of the NMRI strain were treated with the synthetic estrogen diethylstilbestrol (DES), 5 micrograms daily for the first 5 days after birth, or with vehicle only. Levels of LH and FSH (pituitary and serum) and LHRH (hypothalamus) were measured by radioimmunoassay (RIA) in 6- to 56-day-old females with 6- to 7-day intervals. Compared to controls, DES-treated females had low levels of LH on days 6, 12, and 21 in the pituitary, and on days 6 and 12 in serum; increased LH levels were seen in both the pituitary and serum on day 42. The FSH levels of DES-treated females were decreased on days 6 and 12 in the pituitary and on day 6 in serum; an increased FSH content occurred on day 21 in the pituitary. In the preoptic area and basal hypothalamus of DES-treated females, levels of LHRH were increased on day 21 and decreased on day 42. On day 56, the serum levels of FSH and LH and the hypothalamic content of LHRH were similar in controls and DES females. A second study including both synthetic and natural estrogen was performed in 12-day-old females. Treatment with 10(-2) micrograms DES or lower doses or 5 micrograms estradiol-17 beta (E2) on days 1 to 5 after birth had no depressive effect on serum LH. The hypothalamic-pituitary-ovarian feedback system reacted similarly to ovariectomy and E2 challenge in 15-day-old control and DES-treated females. DES-treated 56-day-old females had a reduced LH response to ovariectomy but increased response to exogenous E2 compared to controls. These results show that neonatal treatment with DES has pronounced effects on the hypothalamic-pituitary system in the developing female mouse, which may be of importance for the altered ovarian function in these females as adults.     

Effects of acute exposure to PCBs 126 and 153 on anterior pituitary and thyroid hormones and FSH isoforms in adult Sprague Dawley male rats.

3,3'4,4',5-Pentachlorobiphenyl (PCB 126) and 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) were administered to adult male rats in order to identify sensitive indicators of endocrine disruption. We tested the hypothesis that PCB exposure modifies follicle-stimulating hormone (FSH) pituitary isoforms, as well as the pituitary and serum concentrations of FSH, luteinizing hormone (LH), growth hormone, prolactin, and thyroid-stimulating hormone (TSH). Effects on serum levels of thyroxine (T4) and testosterone (T), and prostate androgen receptor content, were also tested. In one experiment, 5 groups of 8 rats each received two i.p. injections, one day apart, of either corn oil or 6.25, 25, 100 or 400 micrograms/kg/day of PCB 126. Decreases (p < 0.05) in the serum concentrations of T4 and LH started at doses of 25 and 100 micrograms/kg/day, respectively. Serum FSH concentrations were reduced (p = 0.07) in the highest dose group. In contrast, pituitary content of FSH and LH increased with PCB-126 doses (p = 0.004, p = 0.002, respectively). Despite changes in reproductive hormones, PCB-126 had no effect on the androgen receptor content of the prostate. The effect of PCB-126 was tested in the hemicastrated rat, and suggested adverse effects on testosterone secretion. To test the effects of PCB exposure on FSH pituitary isoforms, 4 groups of 10 male rats received two i.p. injections, one day apart, of either corn oil, PCB 153 (25 mg/kg/day), estradiol-17 beta (E2; 20 micrograms/kg/day), or PCB 126 (0.1 mg/kg/day). Serum T4 levels were higher (p < 0.01) in the E2 and PCB 153 groups, and slightly reduced in the PCB 126-treated groups, compared to controls. Simultaneous purification of pituitary FSH and TSH isoforms was performed by HPLC, using two chromatofocusing columns in series. In contrast to TSH isoforms, the distribution of FSH isoforms over the chromatography run differed slightly between treatment groups; the amounts of FSH isoform eluted during the pH gradient were lower (p < 0.05) in E2 and PCB 153-treated rats than in control or PCB 126-treated rats. The similarity between the effects of E2 and PCB 153 on T4 and FSH isoforms supports the contention that PCB 153 possesses estrogenic properties. Serum LH and T4 concentrations were the most sensitive and practical endocrine indicators of PCBs 126 and 153 exposure in male rats.     

Effects of alcohol on E2 beta-stimulated luteinizing hormone in ovariectomized rhesus monkeys.

Anovulation is a frequent concomitant of alcohol abuse, but it has been difficult to assess the acute effects of alcohol on ovulation. Estradiol benzoate (E2 beta) can stimulate a luteinizing hormone (LH) surge in ovariectomized monkeys that appears to be associated with increased luteinizing hormone-releasing hormone (LHRH) pulse frequency and amplitude. The acute effects of alcohol (2.5 and 3.5 g/kg) and an isocaloric sucrose control solution on LH and follicle-stimulating hormone (FSH) secretory activity were studied in five ovariectomized monkeys 41 to 51 hours after administration of E2 beta (42 micrograms/kg, IM). Integrated plasma samples were collected at 20-minute intervals over 10 hours. Under sucrose control conditions, LH increased to 445 and 584 ng/ml within 46 to 49.3 hours after E2 beta administration in two monkeys and high-amplitude LH pulses were evident in three monkeys. Alcohol (2.5 and 3.5 g/kg) significantly decreased the number of LH peaks and valleys (p < 0.01). Peak blood alcohol levels averaged 195 and 291 mg/dl. After 2.5 g/kg alcohol, there was no LH surge or LH pulses in four of five monkeys. A delayed LH surge occurred in one monkey 48 to 50.6 hours after E2 beta when blood alcohol levels decreased to 62 mg/dl. After 3.5 g/kg alcohol, no monkey had an LH surge and pulsatile LH release was significantly reduced in comparison to control conditions (p < 0.01). FSH levels remained stable across alcohol and control conditions. These data suggest that alcohol attenuates pituitary release of LH in response to E2 beta stimulation. These findings are consistent with menstrual cycle disruptions observed in alcohol-dependent women, social drinkers, and in a primate model of alcoholism.     

Study on developmental abnormalities in hypospadiac male rats induced by maternal exposure to di-n-butyl phthalate (DBP)

The objective of this study was to establish a hypospadiac rat model by maternal exposure to di-n-butyl phthalate (DBP) and to evaluate the developmental abnormalities of hypospadiac male rats. Timed-pregnant rats were given DBP by gastric intubation at doses of 0, 250, 500, 750 or 1000 mg/kg body weight (bw)/day from gestation day (GD) 14 to 18 to establish a hypospadiac rat model. The hypospadias was observed in the 500 and 750 mg/kg bw/day groups, the incidence of which was 6.8 and 41.3%, respectively. Transverse serial histological analysis of genitalia of hypospadiac male rats confirmed the malformation. With exposed dose increasing, the serum testosterone (T) levels of male rats inversely decreased, and in the same dosage group the serum T levels of hypospadiac rats were significantly lower than the levels of nonhypospadiac counterparts. The other reproductive lesions such as cryptorchidism and decreased ratio of anogenital distance/body weight (AGD/bw) were also observed. Autopsy analysis revealed the development of reproductive organs (prostate, testes, epididymis, pituitary gland) and nonreproductive organs (adrenal gland, liver, kidney, heart, spleen) of hypospadiac rats and nonhypospadiac counterparts. The results indicated that the reproductive system and developmental condition of hypospadiac male offspring were damaged severely by DBP.     

Endocrine disruption by indole-3-carbinol and tamoxifen: blockage of ovulation

Immature Sprague-Dawley rats received daily doses of indole-3-carbinol (I3C, 0-1.5 g/kg/day), 3,3'-diindolymethane (DIM, 0-400 mg/kg/day), tamoxifen (TAM, 0-0.5 mg/kg/day), or vehicle to determine if their antiestrogenic effects occur by the same mechanism and whether I3C's action is mediated by DIM. Follicular development was induced on day 24 of age by equine chorionic gonadotropin (eCG, 5 IU) 1 day after the initial dose. In a hormone replacement study, human chorionic gonadotropin (hCG, 10 IU sc, 48 h post-eCG) was used to mimic a normal preovulatoy luteinizing hormone (LH) surge following treatment with either I3C or TAM. Blood and ovaries were collected throughout follicular development and the number of ova shed was measured on the morning following expected ovulation (72 h post-eCG). I3C but not TAM reduced body weight gain at higher doses after 4 days of dosing. Ovarian weight gain and ovulation were inhibited by both I3C and TAM in a dose-dependent fashion. During the preovulatory period, both I3C and TAM blocked normal LH and follicle-stimulating hormone (FSH) surges and suppressed serum progesterone (P(4)) profoundly without changing circulating levels of estrogen (E(2)). At the time of expected ovulation, serum E(2) was increased in rats receiving I3C or tamoxifen, whereas serum P(4) was dose-dependently decreased. DIM exerted no significant effects on any of the endpoints studied, even at the highest dose, indicating that the antiestrogenic effects of I3C are not mediated by this metabolite of I3C. hCG successfully restored ovarian weight gain and ovulation in TAM-treated rats. However, hCG only partially reversed the blockage of ovulation by I3C, although ovarian weight gain was restored to normal. In summary, both I3C and TAM block ovulation by altering preovulatory concentrations of LH and FSH, but I3C appears to exert its effect(s) by (a) different mechanism(s) of action. I3C seems to act at both the ovarian and hypothalamic levels by mechanisms similar to those seen in TCDD-treated rats, whereas TAM appears to act only on the hypothalamic-pituitary axis as an anti-estrogen.     

Patent Evaluation: LHRH Peptides as LHRH Antagonists

Summary

Novelty: Glycosylated or polyhydroxylated leutinizing hormone releasing hormone (LHRH) peptides are disclosed and are proposed to possess LHRH antagonist activity. LHRH antagonists are potentially useful for the suppression of gonadotropin (leutinizing hormone, LH) secretion and hence may be useful for the suppression of female ovulation or male spermatogenesis. Glycosylated/polyhydroxylated calcitonins are also disclosed and are potentially useful for reducing plasma calcium levels and maintaining bone mass.

Biology: The glycosylated LHRH peptides were active in suppressing LHRH-induced LH release from rat pituitary cell culture, and in suppressing ovulation in rats, at doses of between 0.0005–10.0 mg/kg sc. The glycosylated calcitonins are stated to have reduced in vivo plasma calcium levels in rats. However, no specific data are presented.

Chemistry: Glycosylation or polyhydroxylation of the peptides is targetted towards the omega-amino groups of peptide lysine residues, the reaction being an Amadori rearrangement mediated by direct rather than N-glycosidic bonding. This method forms a subsidiary part of the claim and is exemplified in twenty-four cases. A specified example is CH₃CO-DPhe(p-Cl)-DPhe(p-Cl)-DTrp-Ser-Tyr-DLys(formyl)-Leu-Lys(N^η-1-deoxyfructosyl)-Pro-DAla-NH₂.     

Acute exposure to molinate alters neuroendocrine control of ovulation in the rat.

Molinate, a thiocarbamate herbicide, has been reported to impair reproductive capability in the male rat and alter pregnancy outcome in a two-generation study. Published data are lacking on the effects of acute exposure to molinate in the female. Based on this work and our previous observations with related dithiocarbamate compounds, we hypothesized that a single exposure to molinate during the critical window for the neural trigger of ovulation on the day of proestrus (PRO) would block the luteinizing hormone (LH) surge and delay ovulation. To examine the effect of molinate on the LH surge, ovariectomized (OVX) rats were implanted with Silastic capsules containing estradiol benzoate to mimic physiological levels on proestrus. Doses of 25 and 50 mg/kg molinate significantly suppressed LH and prolactin secretion. Intact regularly cycling females gavaged with 0, 25, or 50 mg/kg molinate at 1300 h on PRO were examined on estrus or estrus +1 day for the presence of oocytes in the oviduct. All control females had oocytes in the oviduct on estrus. Molinate doses of 6.25 to 50 mg/kg delayed ovulation for 24 h. Estrous cyclicity was examined after daily exposure to 50 mg/kg (21 days). Estrous cyclicity was irregular in the molinate group, showing extended days in estrus. Two experiments were conducted to determine whether molinate blocked the LH surge via a central nervous system (CNS) mode of action or via an alteration in pituitary response. In the first experiment, we evaluated the release of LH in control and molinate-treated rats after a bolus dose of exogenous GnRH. Luteinizing hormone release was comparable in the two groups, suggesting that the effect of molinate is centrally mediated. To further examine the potential role of the CNS, we examined the pulsatile release of LH present in the long-term OVX females. In this model, the pulsatile pattern of LH secretion is directly correlated with GnRH release from the hypothalamus. A significant decrease in the LH pulse frequency was observed in molinate-treated females. These results indicate that molinate is able to delay ovulation by suppressing the LH surge on the day of proestrus and that the brain is the primary target site for the effects on pituitary hormone secretion.     

Atrazine disrupts the hypothalamic control of pituitary-ovarian function.

The chloro-S-triazine herbicides (i.e., atrazine, simazine, cyanazine) constitute the largest group of herbicides sold in the United States. Despite their extensive usage, relatively little is known about the possible human-health effects and mechanism(s) of action of these compounds. Previous studies in our laboratory have shown that the chlorotriazines disrupt the hormonal control of ovarian cycles. Results from these studies led us to hypothesize that these herbicides disrupt endocrine function primarily through their action on the central nervous system. To evaluate this hypothesis, we examined the estrogen-induced surges of luteinizing hormone (LH) and prolactin in ovariectomized Sprague-Dawley (SD) and Long-Evans hooded (LE) rats treated with atrazine (50-300 mg/kg/day, by gavage) for 1, 3, or 21 days. One dose of atrazine (300 mg/kg) suppressed the LH and prolactin surge in ovariectomized LE, but not SD female rats. Atrazine (300 mg/kg) administered to intact LE females on the day of vaginal proestrus was without effect on ovulation but did induce a pseudopregnancy in 7 of 9 females. Three daily doses of atrazine suppressed the estrogen-induced LH and prolactin surges in ovariectomized LE females in a dose-dependent manner, but this same treatment was without effect on serum LH and prolactin in SD females. The estrogen-induced surges of both pituitary hormones were suppressed by atrazine (75-300 mg/kg/day) in a dose-dependent manner in females of both strains evaluated after 21 days of treatment. Three experiments were then performed to determine whether the brain, pituitary, or both organs were the target sites for the chlorotriazines. These included examination of the ability of (1) the pituitary lactotrophs to secrete prolactin, using hypophyosectomized females bearing pituitary autotransplants (ectopic pituitaries); (2) the synthetic gonadotropin-releasing hormone (GnRH) to induce LH secretion in females treated with high concentrations of atrazine for 3 days; and (3) atrazine (administered in vivo or in vitro) to suppress LH and prolactin secretion from pituitaries, using a flow-through perifusion procedure. In conclusion, the results of these studies demonstrate that atrazine alters LH and prolactin serum levels in the LE and SD female rats by altering the hypothalamic control of these hormones. In this regard, the LE female appeared to be more sensitive to the hormone suppressive effects of atrazine, as indicated by the decreases observed on treatment-day 3. These experiments support the hypothesis that the effect of atrazine on LH and prolactin secretion is mediated via a hypothalamic site of action.     

Ovulation in rats is delayed by a substituted triazole

When a single oral dose of 5 or 25 mg/kg of the substituted triazole R151885 [1,1-di(4-fluorophenyl)-2-(1,2,4-triazol-1-yl)-ethanol] was administered at midday on diestrus-2 to rats with regular 4-day estrous cycles, the subsequent ovulation was delayed by 24 or 48 hr, respectively. There was no evidence of toxicity at the doses used. The only morphological changes detected in the reproductive tract were a delay in accumulation of uterine fluid and prolonged but normal follicular maturation prior to the delayed ovulation. The delayed follicles were slightly larger than normal follicles at the time of ovulation. The preovulatory peak plasma concentrations of progesterone, follicle stimulating hormone (FSH), and luteinizing hormone (LH) were delayed by 24 hr in rats treated with 5 mg/kg of R151885 on diestrus-2. Although there was a normal preovulatory peak plasma concentration of estradiol, values were reduced by between 30 to 50% late on diestrus-2 and early on proestrus. Additionally, in ovariectomized rats, 3 daily doses of 25 mg/kg of R151885 antagonized the action of estradiol on the uterus by 45%. We suggest that the reductions in plasma estradiol concentrations during diestrus-2 and proestrus, combined with some antagonism of estradiol's action, may prevent adequate priming of the pituitary thereby suppressing the preovulatory LH surge required for ovulation. The suppression of this LH surge is of a temporary nature indicating a reversible effect of R151885 on the hormonal control system.     

Safety evaluation of alpha-lipoic acid (ALA)

The safety of the antioxidant alpha-lipoic acid (racemic form) (ALA), also called thioctic acid (CAS RN 1077-28-7) was assessed in acute and subchronic toxicity studies as well as in in vitro and in vivo mutagenicity/genotoxicity studies. ALA was not acutely toxic to rats (LD(50)>2000mg/kg bw, OECD method 425). Administration of 31.6 or 61.9mg ALA/kg bw/day for 4 weeks to male/female Wistar rats did not show any adverse effects. Specifically, there was no significant difference between control and treated animals at 31.6 or 61.9mg ALA/kg bw with regard to body weight gain, feed consumption, animal behaviour, or haematological and clinical chemistry parameters. Only the high-dose of 121mg ALA/kg bw was associated with slight alterations in liver enzymes as well as histopathological effects on the liver and mammary gland. ALA did not possess any mutagenic activity in the Ames assays conducted with various bacterial strains of Salmonella typhimurium. Moreover, there was no evidence of genotoxic activity in a mouse micronucleus assay. The results of these studies support the safety of ALA. The no-observed-adverse-effect level (NOAEL) is considered to be 61.9mg/kg bw/day.     

Cadmium-induced hypertension in rats

Chronic cadmium chloride (CdCl2, 0.5 and 1.0 mg/kg, i.p.) treatment in female albino rats for 2 weeks resulted in elevation of blood pressure. In chronic CdCl2-treated rats the pressor responses to different doses of noradrenaline, angiotensin II and depressor responses to acetylcholine and isoprenaline were unaltered. In rat hindquarter preparation there was elevation of perfusion pressure and the sensitivity of vascular bed to noradrenaline was increased in the CdCl2-induced hypertensive rats. Complete bilateral adrenalectomy or chemical sympathectomy or treatment with captopril did not prevent the development of CdCl2-induced hypertension. Treatment with verapamil (15 mg/kg/day, p.o.) or nifedipine (10 mg/kg/day, p.o.) for 2 weeks prevented the development of hypertension with chronic CdCl2 treatment. It is suggested that chronic treatment of rats with CdCl2 induces hypertension. It is possible that cadmium mimics the calcium ion for the induction of hypertension in rats.     

Suppression of the Luteinizing Hormone Surge by Chlordimeform in Ovariectomized,Steroid-Primed Female Rats

Abstract: The midcycle surge of luteinizing hormone (LH) from the pituitary provides the physiological trigger in the mammalian female for the process of ovulation. Accordingly, any agent that compromises the LH surge could function as a reproductive toxicant. Since ovariectomized (OVX) rats implanted with oestradiol capsules will exhibit daily afternoon surges, such animals can serve as a useful model for the investigation of toxicant-induced alterations in this functional hormonal event. The acaricide chlordimeform (CDF) has previously been found to decrease serum LH, probably by altering the hypothalamic noradrenergic transmitter control of LH secretion. Consequently, the present study focused on the effect of acute CDF administration on the appearance of the induced LH surge. Single intraperitoneal injections of CDF (0, 10, 25, 50 mg/kg) in OVX, oestradiol-implanted female Long-Evans rats approximately 5 hr prior to the expected surge caused a complete suppression at 25 and 50 mg/kg. Ten mg/kg had no effect on surge amplitude, but advanced the LH peak by 2 hr. The observed suppression did not persist beyond the day of CDF administration. Earlier dosing at 11 or 18 hr prior to the surge was without effect. Since CDF has been found to elevate serum corticosterone (CORT), 10 mg CORT/rat were given at different times prior to the surge. Twenty hr after administration only a partial lowering was seen; 5 hr exposure were ineffective. This indicates that an indirect adrenal effect was not the principal route, but may accompany an action of CDF on the hypothalamic mechanisms regulating the surge and becomes evident after more prolonged exposure.     

Suppression of the luteinizing hormone surge by chlordimeform in ovariectomized, steroid-primed female rats.

The midcycle surge of luteinizing hormone (LH) from the pituitary provides the physiological trigger in the mammalian female for the process of ovulation. Accordingly, any agent that compromises the LH surge could function as a reproductive toxicant. Since ovariectomized (OVX) rats implanted with oestradiol capsules will exhibit daily afternoon surges, such animals can serve as a useful model for the investigation of toxicant-induced alterations in this functional hormonal event. The acaricide chlordimeform (CDF) has previously been found to decrease serum LH, probably by altering the hypothalamic noradrenergic transmitter control of LH secretion. Consequently, the present study focused on the effect of acute CDF administration on the appearance of the induced LH surge. Single intraperitoneal injections of CDF (0, 10, 25, 50 mg/kg) in OVX, oestradiol-implanted female Long-Evans rats approximately 5 hr prior to the expected surge caused a complete suppression at 25 and 50 mg/kg. Ten mg/kg had no effect on surge amplitude, but advanced the LH peak by 2 hr. The observed suppression did not persist beyond the day of CDF administration. Earlier dosing at 11 or 18 hr prior to the surge was without effect. Since CDF has been found to elevate serum corticosterone (CORT), 10 mg CORT/rat were given at different times prior to the surge. Twenty hr after administration only a partial lowering was seen; 5 hr exposure were ineffective. This indicates that an indirect adrenal effect was not the principal route, but may accompany an action of CDF on the hypothalamic mechanisms regulating the surge and becomes evident after more prolonged exposure.     

Effects of dopamine d2 receptor agonists in a pituitary transplantation-induced hyperprolactinaemia/anovulation model in rats

1. In the present study, we investigated the effects of hyperprolactinaemia, induced by transplantation of anterior pituitary glands under the kidney capsule in female rats, on the relationship between serum and pituitary concentrations of the gonadotropins and on the oestrous cycle. 2. Rats with pituitary transplants showed increased serum prolactin concentrations and decreased serum concentrations of gonadotropins and increased pituitary concentrations of gonadotropins. Moreover, these rats showed persistent dioestrous and anovulation from 3 to 6 days after transplantation. 3. A single oral administration of cabergoline (at doses between 0.001 and 0.1 mg/kg) dose-dependently inhibited the elevated serum prolactin concentrations in hyperprolactinaemic rats. At 0.1 mg/kg, cabergoline induced a continuous reduction in serum prolactin concentrations for 5 days after administration. Terguride (0.1 mg/kg) and bromocriptine (10 mg/kg) also reduced serum prolactin concentrations at 1 and 3 days after administration. All three dopamine D2 receptor agonists increased serum gonadotropin concentrations and ovarian weight at 3 days after administration. 4. In rats exhibiting anovulation, a single oral administration of any one of the three dopamine D2 receptor agonists dose-dependently restored ovulation and a normal oestrous cycle appeared. Oral administration of cabergoline (0.03 mg/kg) or terguride (0.1 mg/kg) restored ovarian function and abolished the anovulation following a reduction in serum prolactin concentrations. However, bromocriptine (10 mg/kg) did not completely abolish anovulation. Following administration of terguride (0.3 mg/kg) or bromocriptine (30 mg/kg), only one normal oestrous cycle appeared; however, following cabergoline (0.1 mg/kg), two normal oestrous cycles appeared. 5. These results suggest that cabergoline has a potent and long-lasting action as a dopamine D2 receptor agonist and, thus, should be a useful drug for the treatment of galactorrhoea and hyperprolactinaemic amenorrhoea and/or anovulation in humans.     

Comparative evaluation of a 5-day Hershberger assay utilizing mature male rats and a pubertal male assay for detection of flutamide's antiandrogenic activity.

A 5-day Hershberger assay utilizing mature male rats and a pubertal male assay were evaluated for the ability to detect antiandrogenic compounds such as flutamide, an androgen receptor antagonist. Six days after the operation, implantation with two silicon capsules containing testosterone (T) (30 mg/capsule) in castrated rats provided the ventral prostate and seminal vesicle weights as well as serum T and luteinizing hormone (LH) levels equivalent to those of the controls (non-castrated, non-implanted rats). Castrated rats implanted with two T-capsules (6 rats/dose) were treated by gavage for 5 days with vehicle (0.5% carboxymethylcellulose) or flutamide (0.15, 0.6, 2.5, or 10 mg/kg/day). Flutamide produced significant decreases in weights of the seminal vesicles and the levator ani plus bulbocavernosus muscles (> or =0.6 mg/kg/day) and ventral prostate (> or =2.5 mg/kg/day), and an increase in serum LH levels (> or =2.5 mg/kg/day), but no changes in serum T levels. When age-matched intact male rats were treated with 10-mg/kg/day flutamide, a significant increase in serum T levels was observed concomitant with a tendency of increased LH. The organ weights were also decreased; however, the changes were less than those in the castrated, T-implanted rats. Immature intact male rats (10 rats/dose) were treated for 20 days with flutamide (0, 0.15, 0.6, 2.5, or 10 mg/kg/day). Flutamide produced significant decreases in weights of the seminal vesicles, ventral prostate, and levator ani plus bulbocavernosus muscles at 2.5 and 10 mg/kg/day. Serum LH levels, but not T levels, were increased at 10 mg/kg/day. Statistical significance of some of these changes was not observed in the 6 animals/dose examined. Our findings support that the Hershberger assay, in the current conditions, is the most sensitive among the assays examined and a useful short-term screening method for the detection of antiandrogenic compounds.     

Curcumin could prevent methemoglobinemia induced by dapsone in rats

The curcumin’s effect given orally by gavage in single- or multiple-dose regimens on methemoglobinemia induced by dapsone (DDS) was investigated in male Wistar rats. In the single-dose regimen, groups of 10 rats received either vehicle alone, or curcumin at 0.1, 1.0, 10, or 30 mg/kg body weight (bw), or curcumin at 0.02, 0.1, 1, 10, or 30 mg/kg bw plus DDS at 40 mg/kg bw, intraperitoneally (i.p.), 2 hours after. In the multiple-dose regimen, groups of 10 rats received either vehicle alone, or curcumin at 0.1, 1.0, 10, or 30 mg/kg bw for 5 days, with or without DDS (40 mg/kg bw, i.p.) 2 hours after on the fifth day. In both regimens, further groups of 10 rats were given DDS alone (positive controls) or normal saline (negative controls) i.p. Single-dose treatment with curcumin at 0.02 and 0.1 mg/kg bw significantly reduced DDS-induced methemoglobin formation, while the higher doses showed a pro-oxidant effect, significantly increasing DDS-induced methemoglobinemia. In the multiple-dose regimen, treatment with curcumin at 0.1 mg/kg bw significantly reduced DDS-induced methemoglobin formation, but the higher doses were without significant effect compared to DDS alone. It is concluded that curcumin at low doses mitigates methemoglobinemia induced by dapsone in rats, both in single- and multiple-dose regimens.