Inhibition of the postcastration rise of luteinizing hormone and follicle-stimulating hormone in female rhesus monkeys (Macaca mulatta) by the administration of a luteinizing hormone-releasing hormone inhibitory analog ([N-Ac-D-Trp1-3,D-p-Cl-phe2,D-Phe6,D-Ala10]-LH-RH)

Castration rapidly decreases hypothalamic gamma-aminobutyric acidergic neuronal activity in both male and female rats

The postcastration LH response is greater and somewhat more rapid in male than female rats. We have previously demonstrated that hypothalamic gamma-aminobutyric acid (GABA)ergic neuronal activity decreases following gonadectomy in male rats. To investigate whether these same hypothalamic GABA neurons decrease their activity postcastration in female rats, and whether more rapid and or greater postcastration decreases occur in male rats, we determined the timing and magnitude of the postcastration decreases in GABA turnover which are associated with the sexually dimorphic postcastration LH response. Adult male and 4-day cycling female rats were castrated between 0800 and 1000 h (females ovariectomized on diestrus day 1). Serum LH levels increased significantly by 12 h postcastration in both males and females with the magnitude of the increases being 6.2-fold in males and 2.8-fold in females. GABA turnover was determined in 16 microdissected brain structures by the GABA transaminase inhibition method at 0 h (sham-operated controls), 6 h, 12 h and 1, 2, 4 and 6 days postcastration. In male rats, in the diagonal band of Broca at the level of the organum vasculosum of the lamina terminalis [DBB(ovlt)], the rate of GABA turnover decreased significantly already by 6 h postcastration compared with the 0 h controls, and remained suppressed through 6 days. This rapid down regulation of DBB(ovlt) GABAergic neurons also occurred in female rats, however, the duration of the decrease was not as prolonged as in male rats. Similar changes occurred in the tuberoinfundibular GABAergic (TIGA) neurons projecting to the median eminence in both males and females. Down regulation of these GABAergic neurons precedes or is coincident with increased postcastration LH secretion in both sexes, and the duration of the decreases is consistent with the less robust postcastration LH response in female rats. In addition, the rate of GABA turnover decreased after castration in the interstitial (bed) nucleus of the stria terminalis, ventral aspect (INSTv), the medial preoptic nucleus, dorsomedial aspect (MPNdm) and the ventromedial nucleus, ventrolateral aspect (VMNvl) in male rats, and in the INSTv and VMNvl of female rats, while there was no effect of castration in other hypothalamic regions or control structures. The result in the female VMNvl is consistent with reports that GABA facilitates lordosis behavior in this hypothalamic structure. These findings are consistent with the hypothesis that discrete hypothalamic populations of sex steroid-sensitive GABAergic neurons mediate the postcastration LH responses in both male and female rats, and may underlie other sexually dimorphic adult phenotypes such as sex behavior.

Antide bioavailability: single dose administration for suppression of testosterone and inhibin in male monkeys

The pharmacokinetics and pharmacodynamics of a single sc injection of Antide on testosterone (T) and inhibin secretion in intact male cynomolgus monkeys were examined. Fifteen primates were randomized to three groups receiving: propylene glycol and water vehicle, 3 mg/kg Antide, and 10 mg/kg of Antide. Antide at the 10 mg/kg dose caused long-term suppression of T ranging from 24-56 days. At the 3 mg/kg dose, suppression of T was of shorter duration. Serum Antide levels were significantly greater in the 10 mg/kg group than the 3 mg/kg group (p less than 0.02), both initially and through 35 days post-treatment. The duration of testosterone inhibition and sustained Antide levels were significantly correlated (p less than 0.01). Inhibin concentrations followed the same general pattern as testosterone reaching a nadir on day 21 post-treatment before subsequent recovery. The prolonged suppressive effect of Antide on T without detectable side effects makes this compound an excellent candidate for clinical evaluation.

Comparison of the subcutaneous and intranasal administration of an LH-RH antagonist ([N-Ac-D-p-Cl-Phe1,2,D-Trp3,D-Arg6,D-Ala10]-LH-RH) in the rhesus monkey

Although luteinizing hormone-releasing hormone (LH-RH) agonists have been administered successfully by other than systemic routes (oral, intranasal (i.n.) and vaginal), there is no evidence that inhibitory analogues may be used in any form other than injectable. In the present study, we compared the effect of two routes of administration: subcutaneous (s.c.), 0.5, 0.2 and 1 mg; and i.n., 0.2, 1 and 5 mg of an LH-RH antagonist, ORG 30276 ([N-Ac-D-p-Cl-Phe1,2,D-Trp3,D-Arg6,D-Ala10]-LH-RH) on gonadotropin levels in oophorectomized monkeys. One hour after s.c. administration, FSH and LH values exhibited a dose-dependent fall that lasted for up to 12 h. After s.c. administration, the maximum inhibition of serum FSH and LH was 29 and 41% (0.2 mg dose) and 41 and 58% (1 mg dose), respectively. After i.n. administration, maximum inhibition of serum FSH and LH was 19 and 40% (1 mg) and 32 and 53% (5 mg), respectively. These decreases were dose-related and lasted for up to 12 h. Analysis of the data revealed that the bioavailability of the i.n. route versus the s.c. route ranged from 16 to 26%. This high effectiveness of the i.n. route in terms of bioavailability is markedly greater than that previously reported for LH-RH agonists (1%) and is probably due to a resistance to enzymatic hydrolysis in the nasal mucosa. These results show for the first time that antagonists of LH-RH can be administered by routes other than parenteral, increasing their potential clinical use in conditions in which inhibition of gonadotropins is desired, as in contraception and in therapy for endometriosis, precocious puberty, and hormone-dependent neoplasms.

The effects of RU486 on the luteal phase of the rhesus monkey

RU486 is a steroid which possesses great affinity for the progesterone (P) receptor, but which has no P activity. It has been shown to be, as a result, a potent P antagonist. In the present study, we investigated the effect of this compound on the luteal phase of the rhesus monkey. The day of ovulation was diagnosed with a +/- 12 h accuracy, using serial laparoscopies and serum estradiol (E2) determinations, in regularly cycling rhesus monkeys. RU486 was administered by gavage (10 mg daily) in different regimens during the luteal phase: Group 1, days 1-5; Group 2, days 5-9; Group 3, days 9-13; and Groups 4, days 9-13, plus hCG (30, 60, 90, 180 and 360 IU i.m. on days 6-10). RU486 induced vaginal bleeding within 24-72 h after the initial administration in Groups 1-3. Animals of Group 4 presented luteal lengths ranging from 9-12 days. Progesterone concentrations at the onset of vaginal bleeding were 2.1 +/- 0.3, 4.9 +/- 0.6, 2.6 +/- 0.4 and 11.2 +/- 1.5 ng/ml (x +/- SEM) for animals of Groups 1-4, respectively. Serum follicle stimulating hormone (FSH), luteinizing hormone (LH), E2 and P levels were not altered during treatment. The availability of a compound such as RU486, that consistently induces vaginal bleeding due to its action at the target level (endometrium) without affecting the hormonal events of the menstrual cycle, opens a new approach to post-coital and interceptive contraception.

Medical hypophysectomy: I. Dose-response using a gonadotropin-releasing hormone antagonist

The hypothalamic-pituitary-ovarian axis can be "dissected" in a nonsurgical and reversible fashion by the administration of a potent gonadotropin-releasing hormone (GnRH) antagonist. We created a transient, functional lesion at the level of the pituitary gonadotrope by using a potent GnRH antagonist ([ Ac- pClPhe1 , pClDPhe2 , DTrp3 , DArg6 , DAla10 ]-GnRH). In long-term castrate cynomolgus monkeys, doses of 0.05 to 2.0 mg/kg/day intramuscularly were administered for a total of 32 days. At doses up to 0.2 mg/kg/day, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in circulation were only moderately suppressed; these subjects responded to an estradiol challenge by manifesting an LH elevation or surge within 48 hours. At doses of 0.5 to 1.0 mg/kg/day, FSH and LH secretion was suppressed to or below the limits of assay detection within 7 days, remaining in a severely hypogonadotropic state for the remainder of the treatment interval. Using 2 mg/kg/day, estradiol-positive feedback for midcycle-like LH/FSH surges was fully inhibited. This suppression of gonadotropin secretion was rapidly reversible, in that circulating gonadotropin levels had returned to pretreatment castrate levels within 60 days after termination of GnRH antagonist treatments. These findings suggest that potent GnRH antagonists can effectively create a hypogonadotropic milieu without the initial enhancement of gonadotropin secretion that occurs during initiation of GnRH agonist therapy. "Medical hypophysectomy" through GnRH antagonist administration may permit a more direct and controlled approach to gonadal therapies such as ovulation induction.

Administration of agonistic and antagonistic analogues of LH-RH induce anovulation in Macaca fasicularis

This study was designed to compare the effects of [N-Ac-D-Trp1,3, D-p-Cl-Phe2, D-Phe6, D-Ala10] (A-LH-RH), an inhibitory analogue, and D-Trp6-LH-RH, an agonist of LH-RH, administered to normally cycling cynomologous monkeys. Animals were divided into three groups (n = 5 each), each group receiving one of the following daily during the first 25 days of the menstrual cycle: 1) 20 micrograms of D-Trp6-LH-RH daily, 2) 1 mg of A-LH-RH, and 3) vehicle. Ovulation was established by serial laparoscopies and serum estradiol measurement. Controls presented normal cycles, as evidenced by ovulation day, luteal phase length and hormone levels. Ovulation was completely inhibited during drug administration in all animals of groups 1 and 2. Luteal phase length of all monkeys that ovulated was normal. The present data, therefore, not only show evidence for a consistent anovulatory effect of agonistic and antagonistic analogues of LH-RH in non-human primates, but also open a new approach for non-steroidal contraception.

Inhibition of prostate tumors by agonistic and antagonistic analogs of LH-RH

We have compared the effects of chronic administration of D-Trp6-LH-RH, a superactive agonist of LH-RH, and a potent antagonist, (NAc-p-Cl-D-Phe1,2,D-Trp3,D-Arg6,D-Ala10)LH-RH, on male Copenhagen F-1 rats bearing the Dunning R-3327H prostate adenocarcinoma. Treatment with 25 micrograms of D-Trp6-LH-RH bid for 21 days decreased the weights of the ventral prostate, testes, and adrenals, but had no effect on the weight of the anterior pituitary gland. Administration of similar doses of the antagonist reduced the weight of the ventral prostate, anterior pituitary gland, and adrenals, but did not change the weight of the testes. Both the agonist and antagonist greatly and significantly reduced tumor weight and volume as compared to controls. Serum LH, prolactin, and testosterone levels in Copenhagen F-1 rats bearing Dunning tumors were significantly decreased after treatment with D-Trp6-LH-RH as well as the antagonist. The inhibition of rat prostate tumors achieved with D-Trp6-LH-RH and the antagonistic analog raised the possibility that these compounds could be used clinically in the treatment of prostate carcinoma and other endocrine-dependent neoplasias. The antagonistic analogs have not yet been tried clinically on a chronic basis. However, the data accumulated so far from clinical trials in men with prostate carcinoma suggest that D-Trp6-LH-RH and other LH-RH agonists can be used for an effective therapy which avoids the side effects of estrogen and the pyschological impact of castration.

Suppression of ovulation in the rat by an orally active antagonist of luteinizing hormone-releasing hormone

A synthetic antagonist of luteinizing hormone-releasing hormone blocked ovulation in rats in a dose-dependent manner when given by gavage on the afternoon of proestrus. Ovulation was delayed for at least 1 day in all animals given 2 milligrams of antogonist and in some of the animals treated with 1 or 0.5 milligram. Oral administration of 2 milligrams also blocked the preovulatory surge of luteinizing hormone. This demonstration that antagonists of luteinizing hormone-releasing hormone can have oral antiovulatory activity clearly enhances their therapeutic potential.

Prostate carcinoma tumor size in rats decreases after administration of antagonists of luteinizing hormone-releasing hormone

The effects of two potent antagonistic analogues of luteinizing hormone-releasing hormone (LH-RH) on the growth of two different models of rat prostate tumors have been investigated. Chronic administration of [NAc-p-F-DPhe1,p-Cl-DPhe2,DTrp3.6,D-Ala10]LH-RH (antagonist I) at 50 micrograms/day for 21 days significantly inhibited the growth of the chemically induced squamous cell carcinoma 11095 in Fisher 344 male rats. The weights of the pituitary, ventral prostate, and testes were not significantly altered. After 21 days of treatment with this analogue serum luteinizing hormone (lutropin), follicle-stimulating hormone, and testosterone levels were markedly decreased. When male Copenhagen F-1 rats bearing the Dunning 3327H prostate adenocarcinoma were injected with antagonist I at 50 micrograms/day for 6 weeks or with [NAc-p-Cl-DPhe1,2,DTrp3,DPhe6,DAla10]LH-RH (antagonist II) at 50 micrograms/day for 17 days, the percentage increase in tumor volume was decreased to half or less and the actual tumor volume was diminished 34-96% compared to controls. Tumor weight was decreased 30% and 89% after antagonist I and, respectively, compared to untreated controls. The tumor doubling time was 3- to 4-fold longer in rats receiving the inhibitory analogues than in the controls. Treatment with antagonist II decreased the weight of the whole prostate, but neither antagonist changed the weight of testes, anterior pituitary gland, or adrenals. Serum luteinizing hormone, follicle-stimulating hormone, and testosterone levels in Copenhagen F-1 rats bearing Dunning tumors were significantly decreased after treatment with the inhibitory analogues, but progesterone levels were increased. The inhibitory effects of these antagonistic analogues on rat prostate tumors suggest that these compound might be considered in the development of new types of therapy for prostate carcinoma and other endocrine-dependent neoplasias.