Antagonism of Female Sexual Behavior with Intracerebral Implants of Antiprogestin RU 38486: Correlation with Binding to Neural Progestin Receptors*

Abstract

The steroidal antiprogestin 17 beta-hydroxyl-11 beta-(4-dimethylaminophenyl)-17 alpha-(1-propynl)estra-4,9-dien-3-one (RU 38486) was administered systemically or was implanted into the ventromedial hypothalamus and other brain regions (habenula, preoptic area, interpeduncular region, in order to determine whether the compound could antagonize progesterone (P) activation of estrous responsiveness and whether the compound would exert its behavioral effects at the presumed site of P action and/or at other neural sites implicated in the regulation of female sexual behavior. RU 38486 (5 mg) administered sc 1 h before 200 micrograms P inhibited P facilitation of lordosis behavior in estrogen-primed rats. Intracerebral application of RU 38486 to the ventromedial hypothalamus reduced lordosis responses in 14 of the 25 animals tested. Similar implants in the habenula also inhibited lordosis in 5 of the 14 animals tested. Antiprogestin implants in the interpeduncular region and preoptic area were virtually without effect (1 of 7 inhibited in each group). Interactions of RU 38486 with steroid binding sites in the hypothalamus-preoptic area (HPOA) were also assessed. RU 38486 appeared to be a competitive inhibitor of progestin ([3H] R5020) binding in HPOA cytosols. Scatchard analysis of [3H]RU 38486 binding showed that when unlabeled P was used as the competitor to assess nonspecific binding, the antiprogestin bound with high affinity [dissociation constant Kd = 8.4 nm] to brain cytosols. In addition, the number of [3H]RU 38486 binding sites in HPOA cytosol increased by approximately 50% in estrogen-primed female rats. Competition studies indicated that unlabeled RU 38486 was the most effective competitor for [3H]RU 38486 binding but that P and R5020 were nearly as effective. Corticosterone, hydrocortisone, deoxycorticosterone, and triamcinolone also competed for [3H]RU 38486 binding but were somewhat less effective than the progestins. Testosterone and estradiol did not displace [3H]RU 38486 except at very high molar excesses. Thus RU 38486 appears to bind with highest affinity to HPOA progestin receptors, but it also binds to glucocorticoid receptors. These data are consistent with the interpretation that inhibition of estrous responsiveness by RU 38486 is associated with the antagonist's interference with brain progestin binding.

In the Ventral Tegmental Area, G-Proteins and cAMP Mediate the Neurosteroid 3α,5α-THP’s Actions at Dopamine Type 1 Receptors for Lordosis of Rats

“…Notably, in both the hypothalamus and midbrain VTA blocking PRs with RU38486 prevented the enhancing effects of SKF38393 on lordosis of hormone-primed rats [19, 37]. However, in the hypothalamus, the PR antagonist RU38486 blocks P-facilitated lordosis [19, 47, 48], but in the VTA it does not [5, 37]. Although RU38486, to the VTA, attenuated SKF38393 and 3α,5α-THP-facilitated lordosis, infusions of RU38486 did not reduce lordosis facilitated by 3α,5α-THP alone [37].…”

Membrane actions of progestins at dopamine type 1-like and GABAA receptors involve downstream signal transduction pathways

“…Classic intracellular PRs are highly expressed in the VMH of rodents and are upregulated by E 2 and/or P 4 coincident with lordosis [8][9][10]. Blocking actions at PRs in the VMH inhibits lordosis of naturally-receptive or ovx, hormone-primed rats [11][12][13][14][15][16]. Administration of PR ligands to ovx, E 2 -primed rats [15], but not PR knockout mice (PRKO), facilitates lordosis [17][18].…”

“…Blocking actions at PRs in the VMH inhibits lordosis of naturally-receptive or ovx, hormone-primed rats [11][12][13][14][15][16]. Administration of PR ligands to ovx, E 2 -primed rats [15], but not PR knockout mice (PRKO), facilitates lordosis [17][18]. The latency for P 4 to enhance lordosis when applied to the VMH of ovx, E 2 -primed rodents is typically several hours [6,[19][20].…”

Ovarian Steroid Regulation of Pulsatile Luteinizing Hormone Release During Early Gestation in the Rat

“…This compound has been shown in the rat to block P receptors in the hypothalamus-preoptic area (20), areas involved in the regulation of pulsatile LH secretion. RU486 has also been reported to initiate LH pulses on estrus in rats following its administration on proestrus (21), and to produce an earlier restoration of pulsatile LH secretion following pup removal from lactating rats (22), effects that were due to antagonism of the negative feedback action of P on pulsatile LH secretion.…”