Progestational and androgenic receptor binding affinities and in vivo activities of norgestimate and other progestins

The progestational and androgenic in vitro receptor binding affinity and the in vivo activity of norgestimate was compared with that of its metabolites and other progestins. The relative binding affinities (RBAs) of norgestimate and its 17-deacetylated metabolite for rabbit uterine progestin receptors were similar to that of progesterone (P); those of 3-keto norgestimate and levonorgestrel were about five times that of P; those of gestodene and 3-keto desogestrel were about nine times that of P. The RBAs of norgestimate, P, and 3-keto norgestimate for rat prostatic androgen receptors were from 0.003 to 0.025 times that of dihydrotestosterone (DHT); those of 3-keto desogestrel, gestodene, and levonorgestrel were from 0.118 to 0.220 times that of DHT. The order of receptor level selectivity represented by the ratio of androgen:progestin IC50 values (with a greater ratio value reflecting a better selectivity) was norgestimate greater than P = 3-keto norgestimate greater than 17-deacetylated norgestimate greater than 3-keto desogestrel greater than gestodene greater than levonorgestrel. In vivo studies demonstrated similar profiles for norgestimate and its 17-deacetylated metabolite. These latter two steroids were equally potent as progestins in stimulating rabbit endometrium, and compared with the other progestins, both steroids exhibited minimal androgenicity as measured by the stimulation of rat prostate growth. In conclusion, these studies, as well as previous preclinical and clinical studies, provide evidence of the selectivity of norgestimate based on minimal androgenicity, indicating an improvement over other progestins used in oral contraceptives.

Profile of an oxytocin antagonist, RWJ 22164 for treatment of preterm labor in laboratory models of uterine contractility

An oxytocin antagonist, 1-deamino-[D-TYR(Oethyl)2,THR4,ORN8]oxytocin (RWJ 22164; dTVT), has recently been characterized in models of uterine contractility. Studies were undertaken to characterize the action of dTVT further on both oxytocin- and vasopressin-induced increases in uterine contractility both in vitro and in situ models and in a model of preterm labor. In these studies, dTVT was found to be a specific competitive inhibitor of both oxytocin- and vasopressin-induced contractions of both pregnant and nonpregnant guinea pig uterus in vitro. In situ, the intravenous administration of dTVT induced a dose-dependent inhibition of oxytocin- and vasopressin-induced contractions in a guinea pig model which measures uterine activity as changes in uterine perfusion pressure. Further studies demonstrated that the intravenous infusion of dTVT delays ongoing labor.

Inhibition of pregnancy before and after implantation in rats with monoclonal antibody against progesterone

A monoclonal antibody against progesterone completely blocked pregnancy when rats were injected intraperitoneally at 0.53 mumol/kg/day on days 1 and 2, or on day 11 of a first pregnancy. The antibody was equally effective when injected again during a second pregnancy. There was no evidence for anti-idiotypic antibody production even when the injection of a heterologous (mouse) antibody was repeated in a second pregnancy.

Evaluation of the anaphylactoid activity of a new LHRH antagonist

ORF 23541 [N-Ac-D-Nal(2)1,D-pCl-Phe2,D-Pal(3)3,Ser4,Nic-Lys5,D-Nic-Lys 6, Leu7, I-Lys8, Pro9,D-Ala10NH2; "Nal-Lys antagonist"] was identified as a potent LHRH antagonist without significant anaphylactoid activity. It blocked ovulation in proestrus rats when administered subcutaneously with an ED50 of 5.8 micrograms/kg. Much higher doses of ORF 23541 than of other antagonists were required to induce a cutaneous anaphylactoid-like reaction. Intradermal administration of ORF 23541 caused an 8.75 x 8.75 mm wheal response with estimated doses of 10.9 and 13.7 micrograms in rats and guinea pigs, respectively. These doses were at least 10 times greater than that required of other LHRH antagonists for the same response. ORF 23541 also did not alter pulmonary function in guinea pigs or dogs when administered intravenously at doses up to 10 mg. These results indicate that ORF 23541 represents a new generation of LHRH antagonists with an improved safety margin.

Anaphylactoid and anti-ovulatory activities of LHRH antagonists in rats

Studies were conducted with LHRH antagonists examining the relationship of structure to anaphylactoid-like activity and the relationship of anaphylactoid-like activity to anti-ovulatory activity in rats. Substitution of basic amino acids appeared to enhance the anaphylactoid-like activity of these peptides but other complex structural characteristics may also be involved. Anaphylactoid and anti-ovulatory activities were clearly independent and potent LHRH antagonists with minimal anaphylactoid-like activity were identified.

Evaluation of 1-deamino-[D-Tyr(Oethyl)2, Thr4, Orn8] vasotocin, an oxytocin antagonist, in animal models of uterine contractility and preterm labor: a new tocolytic agent

We attempted to characterize the ability of a new oxytocin derivative, 1-deamino[D-Tyr(Oethyl)2,Thr4,Orn8] vasotocin (ORF 22164), to antagonize the action of oxytocin in several in vitro and in vivo animal models of uterine hyperactivity. In these studies, the derivative was found to be a specific competitive inhibitor of oxytocin-induced contractions of pregnant guinea pig uterus in vitro. In addition, its intravenous administration induced a dose-dependent inhibition of oxytocin-induced uterine contractions in situ. Finally, like ritodrine, the drug induced a dose-dependent delay of ongoing labor in rats. These results suggest that 1-deamino-[D-Tyr(Oethyl)2,Thr4,Orn8] vasotocin, unlike ritodrine, is a potent and specific antagonist of oxytocin-induced uterine contractions and thus may have potential clinical utility in the treatment of preterm labor.

Characterizing pituitary response to a gonadotropin-releasing hormone (GnRH) antagonist in monkeys: tonic follicle-stimulating hormone/luteinizing hormone secretion versus acute GnRH challenge tests before, during, and after treatment

Pituitary sensitivity to a gonadotropin-releasing hormone (GnRH) challenge test before, during, and after GnRH antagonist administration was compared in four ovariectomized female monkeys receiving GnRH antagonist intramuscularly (IM) at increasing doses of 0.3, 1.0, and 3.0 mg/kg/day over 9 days. Three days before and 3 days after treatment, monkeys received vehicle alone. On experiment days 4, 7, 10, 13, and 16, 100 micrograms of GnRH was administered intravenously (IV) and blood drawn at 0 and 30 minutes. Before treatment, tonic follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels were 248 +/- 105 and 178 +/- 31 ng/ml, respectively; after 0.3 mg/kg/day of GnRH antagonist, FSH and LH decreased to 30 +/- 6 and 41 +/- 4 ng/ml, respectively. After treatment with either 1 mg/kg/day or 3 mg/kg/day of GnRH antagonist, both gonadotropins were undetectable in serum. Monkeys with lower initial levels of gonadotropins were suppressed by 48 hours after GnRH antagonist, while those with higher tonic gonadotropins were suppressed 6 days later (FSH: r = 0.992; LH: r = 0.833). The data show that initial physiologic status is predictive of the rapidity of the suppression response induced by a GnRH antagonist and that, after achieving pituitary suppression, responsivity to an IV GnRH challenge test may be restored before normal tonic FSH/LH secretion is regained.

A comparison of the potencies and activities of progestogens used in contraceptives

The potencies and activities of six progestational agents, norethindrone, levonorgestrel, desogestrel, medroxyprogesterone acetate (MPA), progesterone (P) and norgestimate have been evaluated using standard laboratory bioassays. The endocrine activities measured are those most closely related to the clinically important actions of contraceptives. Relative potencies varied with parameter measured, route of administration and species showing clearly that each progestogen is a distinct pharmacological entity. The order of potency using oral administration for either ovulation inhibition or endometrial stimulation in rabbits was desogestrel greater than levonorgestrel greater than MPA greater than norgestimate greater than norethindrone. Levonorgestrel was more androgenic than desogestrel, and P, norethindrone, norgestimate and MPA were essentially devoid of androgen activity. This profile demonstrates clear differences in the potencies and activities of these progestogens and in their selectivity for target organs.

Sensitivity differences in reproductive/endocrine organs to chronically administered LHRH agonists in female rats

The acute and chronic effects of two LHRH agonists on reproductive endocrine target organs were examined in female rats. Animals were injected twice daily with [(ImBzl)-D-His6,Pro9-NEt]LHRH (histrelin) or [D-Trp6,Pro9-NEt]LHRH for 1, 3, 5, 7, 11 or 28 days at 1, 10, 100 or 1000 micrograms/kg/day beginning in the luteal phase. The responses observed with the two agonists were similar. An initial stimulatory phase was observed on the first day of treatment with substantial increases in serum LH and progesterone levels. A significant diminution of hormone response was seen by day 3. Only 1000 micrograms/kg abolished the pituitary LH response at later treatment periods. Estrous cyclicity, ovarian and uterine weight, and progesterone and estradiol levels were inhibited in a time and dose dependent manner. The results demonstrate target organ sensitivity differences. In contrast to the relatively high doses needed to inhibit the pituitary response and decrease ovarian weight, doses as low as 1 microgram/kg were sufficient to decrease uterine weight. If these findings extrapolate to humans, it may be that conditions in which the desired therapeutic action is suppression of uterine tissue, may be treated with lower doses of LHRH agonists than conditions requiring complete gonadal suppression.

Experimental evidence for failure to implant as a mechanism of infertility associated with endometriosis

The effect of endometriosis on pregnancy, from ovulation through day 14 of pregnancy, was studied in an animal model previously developed and validated with the use of the rabbit. Endometrial tissue was implanted surgically in rabbits and allowed to grow for 11 weeks without hormonal supplementation. The animals were artificially inseminated with semen from bucks with established fertility and human chorionic gonadotropin was administered to induce ovulation. The animals were put to death 1, 4, 8, or 14 days later. The number of corpora lutea and fertilized ova was not affected through day 4. However, on days 8 and 14, a significant reduction in the number of normal fetuses was observed. In a second experiment peritoneal fluid from animals with endometriosis was transferred to normal rabbits 1 day before artificial insemination. A significant reduction in the number of normal fetuses was observed. These studies suggest that failure of nidation due to the maternal environment may be a major factor in infertility associated with endometriosis.

Lack of correlation between fertility and sperm numbers in male rats treated with histrelin, a potent LHRH agonist

Adult male rats were treated daily for up to 8 weeks with histrelin, [(ImBzl)-D-His6, Pro9-NEt]LHRH, to study the antifertility effects of this LHRH agonist. Although serum testosterone concentrations and testicular sperm numbers were significantly decreased by weeks 2 and 4 respectively, a reduction in fertility, as judged by the mean number of fetuses per mated female, was not observed until the sixth week of treatment. Furthermore, the number of spermatozoa in the cauda epididymidis of treated rats did not decrease below initial control levels at any time during the study and full fertility returned within 4 weeks after histrelin treatment was stopped. Thus, the lack of correlation between fertility and testicular and epididymal sperm numbers suggests that the antifertility effects of LHRH agonists are not due solely to reduced sperm numbers, but also result from androgen deficiency.

Multiple actions of a novel vaginal contraceptive compound, ORF 13904

ORF 13904, a sulfonated polystyrene polymer possessing potent vaginal contraceptive activity, was tested in vitro and in vivo to investigate its mechanism of action. Observations of rabbit spermatozoa when mixed with the compound in buffered saline confirmed that the compound is not spermicidal and showed that the cells rapidly and irreversibly agglutinate. Seminal plasma did not compromise the effects of the drug, but rather enhanced them. When spermatozoa were suspended in solutions containing ORF 13904 and then washed thoroughly to remove excess drug, human spermatozoa could not penetrate bovine cervical mucus in vitro and rabbit spermatozoa could not achieve fertilization after artificial insemination in vivo, suggesting that the drug either adheres to the sperm surface or irreversibly compromises sperm function. Biochemical analysis showed that ORF 13904 is also a potent acrosin inhibitor. These experiments suggest that ORF 13904 has several mechanisms of action, including the ability to agglutinate spermatozoa, alter sperm-cervical mucus interaction, and inhibit sperm acrosin.

Role of adrenal androgens in prostate regression in rats treated with an antiandrogen and an LHRH agonist

Histrelin, a potent luteinizing hormone releasing hormone (LHRH) agonist, and flutamide, an antiandrogen, were administered to intact and adrenalectomized rats to determine the role of adrenal androgens in the additive effects of the two drugs on prostate regression. Each compound, given separately, was effective in decreasing prostate weights in intact rats. When given together, additive effects were demonstrated by even greater atrophy of the prostates. It has previously been proposed that this additive effect may be primarily attributed to the ability of the antiandrogen to block the action of adrenal androgens. However, in adrenalectomized rats, the combination of histrelin and flutamide still produced a greater reduction in prostate weights than did either drug alone, indicating that the role of adrenal androgens in this effect is negligible. This experiment also was repeated with castrate, androgen-supplemented rats, and the additive effects previously described were not observed. In a final experiment, prostatic atrophy in castrate rats was not enhanced by either adrenalectomy or flutamide treatment. Thus, the additive effects of histrelin and flutamide appear to focus on testicular rather than adrenal androgens.

Development of an animal model for quantitatively evaluating effects of drugs on endometriosis

The present study was conducted to induce endometriosis in an experimental animal model in which the condition and its response to pharmacologic agents could be quantified. Endometriosis was induced in New Zealand White rabbits by transplanting endometrial sections into various sites throughout the peritoneum. After 7 weeks, the mean implant weight increased in concomitant controls from 10.3 to 89.0 mg. In the next 8 weeks, endometrial implant weight increased to 163.6 mg. Daily subcutaneous administration of a luteinizing hormone-releasing hormone agonist, histrelin, or oral administration of danazol, reduced the ectopic implant weight within 8 weeks to 21.7 and 46.0 mg, respectively. In a group of animals that were bilaterally ovariectomized, implant weight decreased significantly in the same 8-week period to 22.4 mg. Furthermore, histologic analysis of the endometriomas showed that ovariectomy, histrelin, or danazol treatment reduced the number of endometrial glands and atrophied the stroma. We conclude that this animal model represents an excellent method for quantitative evaluation of potential therapeutic agents for endometriosis.

The affinity of norgestimate for uterine progestogen receptors and its direct action on the uterus

Norgestimate is a new orally active progestational agent. Studies were conducted to demonstrate that norgestimate is active pharmacologically without requiring biotransformation to an active metabolite. In in vitro studies, norgestimate exhibited a relatively high affinity for the rabbit uterine progestogen receptor. To demonstrate that norgestimate was not being degraded to a biologically active entity, which was binding to receptor sites in the cytosol preparation, the stability of 14C-norgestimate in the preparation was determined. Following the incubation of 14C-norgestimate with the cytosol fraction used in the receptor assay, the labeled material was extracted and analyzed by reverse phase high performance liquid chromatography. 14C-Norgestimate was recovered from these incubation mixtures, confirming that norgestimate was available to bind to the progestogen receptor. In in vivo studies, norgestimate stimulated the endometrium in immature rabbits when applied directly to the uterus, again suggesting that bio-transformation to an active metabolite is not required for expression of norgestimate's pharmacological activity. These in vitro and in vivo studies, when considered with previously reported studies, show that norgestimate is a unique progestogen.

ORF 13904, a new long-acting vaginal contraceptive

A sulfonated polystyrene polymer, ORF 13904, was discovered in our laboratory to be a highly effective vaginal contraceptive in the rabbit model and to possess a unique mode of action. It was found to be non-spermicidal even at high concentrations, yet it greatly impeded sperm penetration of cervical mucus in vitro. When a gel formulation containing 5% ORF 13904 was administered to rabbits intravaginally, the mean number of fetal implants was reduced dramatically even when coitus was delayed for up to 8 hours or when multiple matings at different time intervals were permitted. The non-spermicidal qualities and extended duration of action of this compound represent major breakthroughs in the development of vaginal contraceptives.

Influence of ovarian steroids on prostaglandin- and leukotriene-induced uterine contractions

The mammalian uterus is capable of metabolizing arachidonic acid via the lipoxygenase pathway, and the uterus responds to lipoxygenase products. We postulated that progesterone influences the production of leukotrienes in the uterus in a way similar to that in which estradiol influences prostaglandin production. Uterine contractions were measured in actively sensitized guinea pigs throughout the estrous cycle and in ovariectomized, hormonally primed, sensitized guinea pigs. Antigen challenge stimulated uterine contractions (caused by prostaglandins) that increased throughout the estrous cycle to a maximum in day 15, when estradiol is at its peak. Pretreatment with indomethacin abolished uterine contractions except on day 9 of the cycle, when progesterone levels are at their highest. Day 9 contractions were blocked by FPL 55712, a selective receptor antagonist of leukotrienes. These findings were confirmed in ovariectomized/sensitized guinea pigs. Our data suggest that endogenous synthesis of leukotrienes in the uterus may be directly related to the rise of progesterone.

Reproductive/endocrine and anaphylactoid properties of an LHRH-antagonist, ORF 18260 [Ac-DNAL1(2), 4FDPhe2,D-Trp3,D-Arg6]-GnRH

It has been demonstrated in a variety of experiments that ORF 18260 inhibits (ED100) spontaneous and LHRH-induced ovulation in rats (10 micrograms/kg s.c.; 10 mg/kg i.g.) and hamsters (100 micrograms/kg s.c. and 100 mg/kg i.g.). Inhibition of LHRH induced ovulation appears to be competitive in nature. In normally cycling animals, efficacy varies with time of administration. In the spontaneously ovulating rat, the most effective time is 15.00 hr of proestrus; in the hamster it is 10.00 hr. Continuous administration inhibits ovulation in rats, and ORF 18260 has contragestational activity in rats and hamsters but not in guinea pigs and mice. Prostate growth in rats is inhibited at a dose of 100 micrograms/kg (s.c.). Our studies also suggest that ORF 18260 can also induce cutaneous anaphylactoid-like reactions in rats. When compound is administered intradermally in rats, ORF 18260 causes a dose-related whealing response, noticeable from the 0.01 micrograms/rat dose level.

In vitro and in vivo comparisons of antiandrogenic potencies of two histamine H2-receptor antagonists, cimetidine and etintidine--HCl

The antiandrogenic potency of cimetidine was compared to that of a new histamine H2-receptor antagonist, etintidine-HCl (ORF 16753-02). Although both compounds displaced [3H]dihydrotestosterone from androgen receptors in vitro and inhibited androgen-stimulated growth of the accessory sex organs of male rats in vivo, etintidine-HCl was significantly less antiandrogenic than cimetidine in the analysis of androgen receptor binding and in the inhibition of seminal vesicle weights. Because etintidine-HCl has been shown previously to have more potent gastric antisecretory activity than cimetidine, its lower antiandrogenic activity suggests that etintidine-HCl has a much wider therapeutic ratio and that its use clinically will result in fewer antiandrogenic side effects.

Effect of androgens and gonadotropins on progesterone secretion of chicken granulosa cells

A culture system has been used to study the effect of PMSG in vivo pretreatment and androgens on the in vitro secretion of progesterone from avian granulosa cells. PMSG in vivo pretreated cells secreted greater amounts of progesterone than did cells obtained from untreated hens. Testosterone and 5-alpha-dihydrotestosterone significantly increased basal progesterone secretion in PMSG pretreated cells as well as in granulosa cells harvested from non-treated hens. Testosterone or 5 alpha-dihydrotestosterone in combination with FSH or LH were additive and never resulted in a synergistic stimulation of progesterone secretion.

Antifertility activity and general pharmacological properties of ORF 13811: a synthetic analog of zoapatanol

ORF 13811, a synthetic analog of zoapatanol, was evaluated in a variety of in vivo and in vitro biological test systems to determine antifertility and uterotonic activity as well as its general pharmacological profile. ORF 13811 is a potent antifertility agent after oral administration in a number of animal species including mice, rats, guinea pigs, dogs and baboons. The single oral ED50 for contragestational activity in the pregnant guinea pig (day 22), mouse (day 16) and rat (day 16) is in the range of 6 to 10 mg/kg. In pregnant beagle dogs, a dose-related contragestational effect was obtained within several days after oral administration of ORF 13811 in the dosage range of 10 to 30 mg/kg. ORF 13811, when administered to pregnant baboons, caused dose-related vaginal bleeding and evacuation of uterine contents within 3 days following treatment with oral doses of 40 to 60 mg/kg. Serum progesterone levels were decreased in baboons and the degree of reduction correlated with contragestational activity. ORF 13811 was also effective in inhibiting implantation in mice, rats and hamsters, but required higher dose levels than those of the post-implantive treatments. In vitro uterotonic properties of ORF 13811 were demonstrated by its ability to induce contraction of uterine strips obtained from female guinea pigs at two different reproductive stages (day 15 of the estrous cycle and day 22 of pregnancy). In these preparations ORF 13811 was approximately 1/30 to 1/50th as potent as PGF2 alpha. In a series of pharmacological tests, ORF 13811 was found to possess slight sedative properties but was devoid of activity on pulmonary, gastrointestinal, and immune systems as well as in a number of biochemical tests, data not reported here. However, in cardiovascular studies, ORF 13811 appears to possess a vasoconstrictor profile in the dog, monkey and baboon as indicated by an increase in mean arterial blood pressure as well as total peripheral and regional vascular resistances. The in vitro pharmacological profile of ORF 13811 was examined in myocardial tissue and vascular smooth muscle test systems and compared to PGF2 alpha. ORF 13811 was found to contract rat aortic strips, 15 times less potent than PGF2 alpha. The compound had no direct effect on isolated guinea pig atria or papillary muscle. In summary, ORF 13811 is a potent orally active antifertility agent characterized primarily as a contractor of uterine and vascular smooth muscle.

Evaluation of drugs for arrest of premature labor in a new animal model

Reported are pharmacologic data from a new animal model used for evaluating drugs from several therapeutic classes for their potential use in the treatment of premature labor. This model measures the spontaneous delivery time between the first and second rat pups in a term pregnancy. In control animals, this averaged 16.3 +/- 4.2 minutes. Ethanol (3.5 gm/kg) and the beta-agonists ritodrine (12.5 mg/kg) and albuterol (0.25 mg/kg) significantly delayed delivery of the second pup. The calcium blockers nifedipine, verapamil, and diltiazem were the most active of all compounds tested in this model. The nonsteroidal anti-inflammatory agents indomethacin and naproxen were inactive at doses as high as 5 and 25 mg/kg, respectively. Metiamide, an H2-antagonist, and dimenhydrinate, an H1-antagonist, were inactive.

Comparative effect of estriol and equine conjugated estrogens on the uterus and the vagina

Estriol has been reported to act selectively on the vagina and cervix without causing endometrial proliferations. Studies comparing this effect of estriol to that of equine conjugated estrogens after intravaginal administration have not been reported. In this study, intravaginally administered Ortho- Gynest which contains estriol, and Premarin which contains equine conjugated estrogens, were evaluated for their ability to stimulate vaginal maturation and uterine growth in rats. Approximately 15 times more conjugated estrogens than estriol was needed to induce the same degree of vaginal cornification in castrated rats. In contrast, estriol was less potent than the conjugated estrogens in causing uterine growth in immature rats after subcutaneous administration in sesame oil and in mature rats after intravaginal administration in cream preparations. In studies evaluating the vaginal irritation potential of estriol vaginal cream, the irritation exhibited by treated rabbits was found to be comparable to that of sham-treated control rabbits. Estriol was well-tolerated in an oral acute safety study in rats.