Analgesic effects of the putative FSH-suppressing gonadal steroid, 3 alpha-hydroxy-4-pregnen-20-one: possible modes of action

Assessment of pregnenolone effects on alcohol intake and preference in male alcohol preferring (P) rats

Neuroactive steroids can modulate a variety of neurobehavioral functions via the GABAergic system. This study was conducted to determine the importance of the neurosteroid pregnenolone on the regulation of alcohol intake. The effects of acute and chronic administration of pregnenolone on alcohol intake were assessed in alcohol preferring (P) rats. The rats were injected i.p. with the vehicle or pregnenolone (25, 50 or 75 mg/kg) and their alcohol and water intake were recorded at 2, 4, 6 and 24 h. Also, the chronic effects of 50 mg/kg (i.p.) pregnenolone on alcohol intake were determined. Our results show that although the main effect of i.p. injection of pregnenolone in reducing alcohol intake was not quite significant compared with the vehicle, pregnenolone at 75 mg/kg significantly (P<0.025) reduced alcohol intake. Regarding alcohol preference, acute administration of pregnenolone both at 50 mg/kg (P<0.05) and at 75 mg/kg (P<0.025) significantly reduced alcohol preference. In chronic experiments pregnenolone given for 10 consecutive days did not show a significant effect on alcohol intake and alcohol preference. Overall, although pregnenolone given i.p. acutely and significantly reduced alcohol intake and preference, the fact that chronic treatment did not show an effect diminishes its promise to be considered for the treatment of alcoholism. However, its profile of effects might be different in human alcoholics.

Progestogens and brain: an update

Each synthetic progestins has its own specific activities on different tissues, which can vary significantly between progestins of different classes and even within the same class. Indeed, different progestins may support or oppose the effects of estrogen depending on the tissue, thereby supporting the concept that the clinical selection of progestins for HRT is critical in determining potential positive or detrimental effects. These actions might be particularly relevant in the central nervous system (CNS) where progesterone (P) has pivotal roles besides reproduction and sexual behavior, going from neuropsychological effects to neuroprotective functions. Growing evidence supports the idea that synthetic progestins differ significantly in their brain effects, and clinical studies indicate that these differences also occur in women. Molecular and cellular characterization of the signaling properties of synthetic progestins in brain cells is therefore required and is hoped will lead to a better clinical utilization of the available compounds, as well as to new concepts in the engineering of new molecules. The aim of the present paper is to briefly review and compare neuroendocrine effects of progestogens with special reference to P metabolism into neuroactive steroids and the opioids system.

From MIF-1 to endomorphin: the Tyr-MIF-1 family of peptides

The Tyr-MIF-1 family of small peptides has served a prototypic role in the introduction of several novel concepts into the peptide field of research. MIF-1 (Pro-Leu-Gly-NH(2)) was the first hypothalamic peptide shown to act "up" on the brain, not just "down" on the pituitary. In several situations, including clinical depression, MIF-1 exhibits an inverted U-shaped dose-response relationship in which increasing doses can result in decreasing effects. This tripeptide also can antagonize opiate actions, and the first report of such activity also correctly predicted the discovery of other endogenous antiopiate peptides. The tetrapeptide Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH(2)) not only shows antiopiate activity, but also considerable selectivity for the mu-opiate binding site. Tyr-W-MIF-1 (Tyr-Pro-Trp-Gly-NH(2)) is an even more selective ligand for the mu receptor, leading to the discovery of two more Tyr-Pro tetrapeptides that have the highest specificity and affinity for this site. These are the endomorphins: endomorphin-1 is Tyr-Pro-Trp-Phe-NH(2) and endomorphin-2 is Tyr-Pro-Phe-Phe-NH(2). Tyr-MIF-1 proved, contrary to the then prevailing dogma, that peptides can be saturably transported across the blood-brain barrier by a quantifiable transport system. Unexpectedly, the Tyr-MIF-1 transporter is shared with Met-enkephalin. In the era in which it was doubtful whether a peripheral peptide could exert CNS effects, the Tyr-MIF-1 family of peptides also explicitly showed that they can exert more than one central action that persists longer than their half-lives in blood. These peptides clearly illustrate that the name of a peptide restricts neither its actions nor its conceptual implications.

Neurosteroids in the context of stress: implications for depressive disorders

Animal models indicate that the neuroactive steroids 3alpha,5alpha-THP (allopregnanolone) and 3alpha,5alpha-THDOC (allotetrahydroDOC) are stress responsive, serving as homeostatic mechanisms in restoring normal GABAergic and hypothalamic-pituitary-adrenal (HPA) function following stress. While neurosteroid increases to stress are adaptive in the short term, animal models of chronic stress and depression find lower brain and plasma neurosteroid concentrations and alterations in neurosteroid responses to acute stressors. It has been suggested that disruption in this homeostatic mechanism may play a pathogenic role in some psychiatric disorders related to stress. In humans, neurosteroid depletion is consistently documented in patients with current depression and may reflect their greater chronic stress. Women with the depressive disorder, premenstrual dysphoric disorder (PMDD), have greater daily stress and a greater rate of traumatic stress. While results on baseline concentrations of neuroactive steroids in PMDD are mixed, PMDD women have diminished functional sensitivity of GABA(A) receptors and our laboratory has found blunted allopregnanolone responses to mental stress relative to non-PMDD controls. Similarly, euthymic women with histories of clinical depression, which may represent a large proportion of PMDD women, show more severe dysphoric mood symptoms and blunted allopregnanolone responses to stress versus never-depressed women. It is suggested that failure to mount an appropriate allopregnanolone response to stress may reflect the price of repeated biological adaptations to the increased life stress that is well documented in depressive disorders and altered allopregnanolone stress responsivity may also contribute to the dysregulation seen in HPA axis function in depression.

The relationship of allopregnanolone immunoreactivity and HPA-axis measures to experimental pain sensitivity: Evidence for ethnic differences

In animal models, allopregnanolone (ALLO) negatively modulates the hypothalamic-pituitary-adrenal (HPA) axis and has been shown to exert analgesic effects. The purpose of this study was to assess the relationship between plasma ALLO immunoreactivity (ALLO-ir), HPA-axis measures, and pain sensitivity in humans. Forty-five African Americans (21 men, 24 women) and 39 non-Hispanic Whites (20 men, 19 women) were tested for pain sensitivity to tourniquet ischemia, thermal heat, and cold pressor tests. Plasma ALLO-ir, cortisol, and beta-endorphin concentrations were taken following an extended rest period. Lower concentrations of ALLO-ir were associated with increased pain tolerance to all three pain tests and increased pain threshold to the thermal heat pain task in the non-Hispanic Whites only (rs=-.35 to -.49, ps<.05). Also, only in the non-Hispanic Whites was cortisol associated with thermal heat tolerance (r=+.39, p<.05) and threshold (r=+.50, p<.01) and cold pressor tolerance (r=+.32, p<.05), and were beta-endorphin concentrations associated with cold pressor tolerance (r=+.33, p<.05). Mediational analyses revealed that higher cortisol levels mediated the relationship between lower ALLO-ir and increased thermal heat pain threshold in the non-Hispanic Whites only. These results suggest that lower ALLO-ir concentrations are associated with decreased pain sensitivity in humans, especially in non-Hispanic Whites, and that this relationship may be mediated by HPA-axis function.

Subjective effects and changes in steroid hormone concentrations in humans following acute consumption of alcohol

BACKGROUND

GABAA receptors are an important site of action of endogenous neurosteroids and an important mediator of several behavioral effects of alcohol. This study examined the effects of alcohol on plasma steroid hormone concentrations on the hypothesis that the endocrine effects mediate some of the subjective effects of alcohol.

METHODS

Thirty-two healthy subjects (17 men) with no history of a substance use disorder participated in this human laboratory study. All subjects consumed three standard drinks of grain alcohol. Subjective measures and blood samples for steroid concentrations were collected at baseline and 40 min after alcohol consumption.

RESULTS

Alcohol increased self-reported stimulation, alcohol liking, and desire for more alcohol. Alcohol also increased pregnenolone (PREG) and dehydroepiandrosterone (DHEA) concentrations, while it decreased progesterone (PROG) and allopregnanolone (ALLO) concentrations, as well as ALLO/PREG and PROG/PREG ratios. In men, the change in PREG concentration was significantly correlated with alcohol liking, while the alcohol-induced change in ALLO concentration correlated significantly with both alcohol liking and desire for more alcohol.

DISCUSSION

These findings provide preliminary support for the hypothesis that endogenous neurosteroids mediate some of the subjective effects of alcohol. Efforts to replicate these findings should aim to specify more clearly the nature and time course of the effects.

Estrogen and/or progesterone administered systemically or to the amygdala can have anxiety-, fear-, and pain-reducing effects in ovariectomized rats

Estrogen (E2) and/or progesterone (P) in the amygdala may influence anxiety, fear, and pain behaviors. Ovariectomized rats were administered subcutaneous or intra-amygdala vehicle, E2, P, or E2 + P: Effects on open field, elevated plus-maze, defensive freezing, and hot-plate task performance were observed. Subcutaneous E2 + P or intra-amygdala E2, P, or E2 + P increased open field central entries and open arm time in the plus-maze compared with vehicle. Subcutaneous or intra-amygdala E2, P, or E2 + P decreased time spent freezing postshock compared with vehicle. Subcutaneous or intra-amygdala E2 + P increased latencies to lick paws compared with vehicle. Thus, E2 and P may have effects in the amygdala to decrease anxiety, fear, and/or pain responses.

Expression of progesterone metabolizing enzyme genes (AKR1C1, AKR1C2, AKR1C3, SRD5A1, SRD5A2) is altered in human breast carcinoma

BACKGROUND

Recent evidence suggests that progesterone metabolites play important roles in regulating breast cancer. Previous studies have shown that tumorous tissues have higher 5alpha-reductase (5alphaR) and lower 3alpha-hydroxysteroid oxidoreductase (3alpha-HSO) and 20alpha-HSO activities. The resulting higher levels of 5alpha-reduced progesterone metabolites such as 5alpha-pregnane-3,20-dione (5alphaP) in tumorous tissue promote cell proliferation and detachment, whereas the 4-pregnene metabolites, 4-pregnen-3alpha-ol-20-one (3alphaHP) and 4-pregnen-20alpha-ol-3-one (20alphaDHP), more prominent in normal tissue, have the opposite (anti-cancer-like) effects. The aim of this study was to determine if the differences in enzyme activities between tumorous and nontumorous breast tissues are associated with differences in progesterone metabolizing enzyme gene expression.

METHODS

Semi-quantitative RT-PCR was used to compare relative expression (as a ratio of 18S rRNA) of 5alphaR type 1 (SRD5A1), 5alphaR type 2 (SRD5A2), 3alpha-HSO type 2 (AKR1C3), 3alpha-HSO type 3 (AKR1C2) and 20alpha-HSO (AKR1C1) mRNAs in paired (tumorous and nontumorous) breast tissues from 11 patients, and unpaired tumor tissues from 17 patients and normal tissues from 10 reduction mammoplasty samples.

RESULTS

Expression of 5alphaR1 and 5alphaR2 in 11/11 patients was higher (mean of 4.9- and 3.5-fold, respectively; p < 0.001) in the tumor as compared to the paired normal tissues. Conversely, expression of 3alpha-HSO2, 3alpha-HSO3 and 20alpha-HSO was higher (2.8-, 3.9- and 4.4-fold, respectively; p < 0.001) in normal than in tumor sample. The mean tumor:normal expression ratios for 5alphaR1 and 5alphaR2 were about 35-85-fold higher than the tumor:normal expression ratios for the HSOs. Similarly, in the unmatched samples, the tumor:normal ratios for 5alphaR were significantly higher than the ratios for the HSOs.

CONCLUSIONS

The study shows changes in progesterone metabolizing enzyme gene expression in human breast carcinoma. Expression of SRD5A1 (5alphaR1) and SRD5A2 (5alphaR2) is elevated, and expression of AKR1C1 (20alpha-HSO), AKR1C2 (3alpha-HSO3) and AKR1C3 (3alpha-HSO2) is reduced in tumorous as compared to normal breast tissue. The changes in progesterone metabolizing enzyme expression levels help to explain the increases in mitogen/metastasis inducing 5alphaP and decreases in mitogen/metastasis inhibiting 3alphaHP progesterone metabolites found in breast tumor tissues. Understanding what causes these changes in expression could help in designing protocols to prevent or reverse the changes in progesterone metabolism associated with breast cancer.

Anti-nociception following exposure to trimethylthiazoline, peripheral or intra-amygdala estrogen and/or progesterone

Estradiol (E(2)) and/or progesterone (P) to the amygdala may influence stress-induced analgesia following predator odor, trimethylthiazoline (TMT), exposure. Ovariectomized (ovx) rats were administered subcutaneous (SC) or intra-amygdala vehicle, E(2), P, or E(2)+P. The effects on performance in a test of pain sensitivity, the tailflick task, was observed in animals that experienced an acute exposure to TMT or no odor (control) in a small chamber. Rats that were exposed to TMT had increased tailflick latencies compared to rats not exposed to TMT, this was partially attenuated by the opiate antagonist naloxone. Systemic E(2), P, or E(2)+P increased tailflick latencies compared to vehicle administration to ovx rats. Ovx rats administered E(2)+P to the amygdala had increased tailflick latencies compared to control rats. These data suggest that following exposure to predator odor, pain sensitivity in the tailflick task is decreased and that E(2) and/or P may have actions in the amygdala to produce similar anti-nociceptive effects.

Biosynthesis of the neurosteroid 3 alpha-hydroxy-4-pregnen-20-one (3 alpha hp), a specific inhibitor of FSH release

The gonadal steroid 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP) is a neuroactive steroid with anxiolytic and analgesic actions. In addition, 3 alpha HP has been shown to inhibit GnRH activity on gonadotropes and selectively suppress FSH release from pituitary cells, without an effect on LH. The enzyme 3 alpha-hydroxysteroid dehydrogenase (3 alpha HSD) has been presumed to be the enzyme responsible for the conversion of progesterone to 3 alpha HP, but this has never been confirmed in vitro or in vivo. We have now determined the mechanism of 3 alpha HP synthesis in vivo using specific enzyme inhibitors and in vitro using recombinant proteins. Incubation of [(3)H]progesterone with purified recombinant rat and human 3 alpha HSD isoforms showed that both the rat 3 alpha HSD and the human type 2(brain) 3 alpha HSD converted progesterone to 3 alpha HP. Age-dependent 3 alpha HP production was demonstrated in pituitary and cortex. Incubation of both tissues with indomethacin, a known 3 alpha HSD inhibitor, decreased the conversion of progesterone to 3 alpha HP by at least 70%, indicating that 3 alpha HSD was responsible for this conversion. As human type 2 3 alpha HSD is expressed in a region-specific fashion in the brain, 3 alpha HP may only be made in specific regions of the brain. Furthermore, the data suggest that the pituitary has the capacity for 3 alpha HP production, which may provide an additional mechanism for regulation of GnRH action.

Antinociceptive effects of the neuroactive steroid, 3alpha-hydroxy-5alpha-pregnan-20-one and progesterone in the land snail, Cepaea nemoralis

Results of investigations with vertebrates have implicated neuroactive steroids and in particular 5alpha-reduced metabolites of progesterone such as 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP/3A5P and originally allopregnanolone) in the rapid modulation of diverse functions including that of nociceptive sensitivity. These effects have been indicated to involve modulation of GABA receptors. Results of recent phylogenetic studies have revealed the presence of GABA receptors in invertebrates that may also be subject to modulation by steroids and neuroactive steroids. The present study examined the effects of the neuroactive steroid, 3alpha-hydroxy-5alpha-pregnan-20-one, as well as progesterone on aversive thermal (nociceptive) responses in a mollusc, the land snail, Cepaea nemoralis. 3alpha-Hydroxy-5alpha-pregnan-20-one had significant dose-related (0.01-1.0 microg) antinociceptive effects in Cepaea increasing the latency of response to a 40 degrees C surface, with maximum effects being evident 15-30 min after administration. These effects of 3alpha-hydroxy-5alpha-pregnan-20-one were stereospecific, with the stereoisomer 3beta-hydroxy-5alpha-pregnan-20-one (3B5P) failing to affect nociceptive responses. Progesterone also had significant dose-related (0.10-10 microg) antinociceptive effects that, however, were delayed in onset and relatively prolonged (60-120 min), suggestive of the formation of active metabolites. The presence of endogenous progesterone (12.36+/-0.17 ng/g tissue) was ascertained by a radioimmunoassay further supporting a functional role for steroids in Cepaea. The antinociceptive effects of 3alpha-hydroxy-5alpha-pregnan-20-one and progesterone were blocked by the GABA antagonists, bicuculline and picrotoxin, while being relatively insensitive to opioid and N-methyl-D-aspartate antagonists. These results suggest an early evolutionary development and phylogenetic continuity of neuroactive steroid and GABA involvement in the mediation of nociception.

Forebrain mechanisms of nociception and pain: analysis through imaging

Pain is a unified experience composed of interacting discriminative, affective-motivational, and cognitive components, each of which is mediated and modulated through forebrain mechanisms acting at spinal, brainstem, and cerebral levels. The size of the human forebrain in relation to the spinal cord gives anatomical emphasis to forebrain control over nociceptive processing. Human forebrain pathology can cause pain without the activation of nociceptors. Functional imaging of the normal human brain with positron emission tomography (PET) shows synaptically induced increases in regional cerebral blood flow (rCBF) in several regions specifically during pain. We have examined the variables of gender, type of noxious stimulus, and the origin of nociceptive input as potential determinants of the pattern and intensity of rCBF responses. The structures most consistently activated across genders and during contact heat pain, cold pain, cutaneous laser pain or intramuscular pain were the contralateral insula and anterior cingulate cortex, the bilateral thalamus and premotor cortex, and the cerebellar vermis. These regions are commonly activated in PET studies of pain conducted by other investigators, and the intensity of the brain rCBF response correlates parametrically with perceived pain intensity. To complement the human studies, we developed an animal model for investigating stimulus-induced rCBF responses in the rat. In accord with behavioral measures and the results of human PET, there is a progressive and selective activation of somatosensory and limbic system structures in the brain and brainstem following the subcutaneous injection of formalin. The animal model and human PET studies should be mutually reinforcing and thus facilitate progress in understanding forebrain mechanisms of normal and pathological pain.

Brief exposure of mice to 60 Hz magnetic fields reduces the analgesic effects of the neuroactive steroid, 3alpha-hydroxy-4-pregnen-20-one

Relatively weak, extremely low frequency (ELF), magnetic fields have been shown to exert a variety of biological effects, although the modes of action remain to be established. Neuroactive steroids and neurosteroids have been shown to produce a diverse range of rapid centrally mediated behavioral and physiological effects that are reported to be sensitive to magnetic fields. Here we show that brief exposure of male mice to an ELF magnetic field (30 min, 60 Hz, 141 microT peak) significantly reduces the analgesic effects arising from intracerebroventricular (i.c.v.) administration of the centrally produced allylic neuroactive steroid, 3alpha-hydroxy-4-pregnen-20-one (3alphaHP) and that the dihydropyridine (DHP) calcium channel antagonists, diltiazem and nifedipine, block the inhibitory effects of the 60 Hz ELF on 3alphaHP-induced analgesia. These results indicate that exposure to 60 Hz ELF affects the analgesic effects of neuroactive steroids such as 3alphaHP through alterations in calcium channel function. These findings raise the possibility that ELF magnetic fields may, in part, exert their actions through effects on diverse neuroactive steroid modulated processes.

Ring A reductions of progestins are not essential for estrous behavior facilitation in estrogen-primed rats

In Experiment 1 six dose levels (range 0.66-2000 microg) of progesterone (P) and two synthetic progestins with a double bond at C6: megestrol acetate (MA) and chlormadinone acetate (CA), which cannot be reduced at C5, were injected to estrogen-primed (2 microg estradiol benzoate 42 h earlier) ovariectomized (ovx) rats. The three progestins elicited significant lordosis and proceptive behaviors. Potency analysis showed that MA was the most potent progestin for stimulating estrous behavior, followed by P and CA. These results suggest that ring A reduction of progestins to 5alpha/5beta metabolites is not essential for the facilitation of estrous behavior in ovx estrogen-primed rats. Progestins with the 3-ketone group and a double bond at C4 can also be reduced at C3 to yield 3alpha-hydroxysteroid metabolites potentially capable of stimulating estrous behavior. In Experiment 2, the relevance of the formation of 3alpha-hydroxysteroid metabolites for estrous behavior facilitation was tested by concurrently injecting indomethacin (1.5 mg), a blocker of 3alpha-hydroxysteroid oxidoreductase, with 400 microg of P, MA, or CA to ovx estrogen-primed rats. Indomethacin failed to block the stimulatory effect of these progestins on estrous behavior. These results suggest that 3-ketosteroid reduction is also not essential for estrous behavior facilitation by progestins.

Synthesis, metabolism and levels of the neuroactive steroid, 3alpha-hydroxy-4-pregnen-20-one (3alphaHP), in rat pituitaries

The neuroactive steroid, 3a-hydroxy-4-pregnen-20-one (3alphaHP), is a metabolite of progesterone and a precursor of 3alpha-hydroxy-5alpha-pregnan-20-one (5alphaP3alpha; allopregnanolone). In addition to analgesic and anxiolytic effects by interaction with the GABA(A) receptor complex, 3alphaHP regulates pituitary FSH secretion by rapid non-genomic interaction with the Ca2+-driven cell signaling mechanisms. Since gonadectomy and adrenalectomy do not result in elimination of 3alphaHP, and since there is the possibility of paracrine and/or autocrine regulation of FSH release, the capacity of pituitary cells to regulate levels (by synthesis, metabolism, and storage) of 3alphaHP was examined. Anterior pituitaries from random cycling female rats were incubated, either as fragments or as cultured cells, for 1, 4 or 8 h with 3H- or 14C-labeled progesterone. The steroid metabolites were identified by thin-layer chromatography, autoradiography, high pressure liquid chromatography (HPLC), derivatization and GC/MS. Pituitary cells actively converted progesterone to 3alphaHP along with 5alphaP3alpha, 5alpha-pregnane-3,20-dione, 20alpha-hydroxy-5alpha-pregnan-3-one, 3beta-hydroxy-5alpha-pregnan-20-one, 5alpha-pregnane-3alpha(beta), 20alpha-diols, 20alpha-hydroxy-4-pregnen-3-one, and 4-pregnene-3alpha(beta), 20alpha-diols. The results indicate the presence of the following steroidogenic enzymes in anterior pituitary cells: 3alpha-hydroxysteroid oxidoreductase (3alpha-HSO), 20alpha-HSO, 3beta-HSO, and 5alpha-reductase. The activities of 5alpha-reductase and 3alpha-HSO were approximately equal and greatly exceeded those of the other enzymes. After 8 h of incubation with 100 ng progesterone per pituitary, about 20% of the progesterone was metabolized and 3.18 ng of 3alphaHP had been formed. The accumulation of 3alphaHP increased approximately linearly with the time of incubation. Metabolism studies using [1,2,6,7-(3)H]3alphaHP showed that pituitary cells convert about 29% and 8% of the 3alphaHP to progesterone and 5alphaP3alpha, respectively, in 2 h. Specific radioimmunoassays determined 11.6 and 7.5 ng of 3alphaHP per pituitary, respectively, in 25- and 40-day-old non-cycling female rats; these concentrations of 3alphaHP were about 2-3-fold greater than those of progesterone in the same pituitaries. In older (80-100 days old) cycling rats, the levels of 3alphaHP were about 9.4 and 18.6 ng/pituitary at 13.00 h and 22.00 h, respectively, on the day of proestrus, while the concomitant circulating levels were 13.7 and 5.4 ng/ml. The results indicate a marked capacity of rat pituitary cells to synthesize the neuroactive and FSH regulating steroid, 3alphaHP, from progesterone, and in turn to metabolize 3alphaHP to the neurosteroid, allopregnanolone, and to progesterone. The studies suggest cyclic biosynthetic and metabolic pathways for 3alphaHP and other steroids in the pituitary. They also indicate that the regulation of FSH secretion by 3alphaHP may be (in part, or in whole) via paracrine or autocrine mechanisms.

Acute, nongenomic actions of the neuroactive gonadal steroid, 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP), on FSH release in perifused rat anterior pituitary cells

We have previously shown that the gonadal and neurosteroid, 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP), can selectively suppress gonadotrophin-releasing hormone (GnRH) induced follicle-stimulating hormone (FSH) release from static cultures of anterior pituitary cells during a 4-h incubation period. The actions appeared to be at the level of the gonadotroph membrane and the cell signaling pathway involving Ca2+ and protein kinase C (PKC). In order to investigate further if the effects of 3 alpha HP on FSH release are generated by nongenomic mechanisms, we monitored the short-term effects of 3 alpha HP using dispersed anterior pituitary cells in a low dead-volume perifusion system with short (< or = 5 min) exposures to the steroid. Pulses of GnRH (10(-8) or 10(-7) M) lasting 2-5 min resulted in marked peaks of FSH release, and the variation in FSH amounts released from the cells in a particular column were minimal if the interval between successive GnRH pulses was at least 3-4 h. A 5-min pulse of 3 alpha HP (10(-9) M) administered simultaneously with the GnRH pulse suppressed GnRH-induced FSH release. On the other hand, similar treatment with the stereoisomer 3 beta-hydroxy-4-pregnen-20-one (3 beta HP), had no effect, but progesterone and estradiol pulses augmented the GnRH-induced FSH release. Pretreatment of cells with a 5-min pulse of 3 alpha HP, at 120, 60, or 30 min prior to a GnRH pulse suppressed the GnRH-induced FSH release. The suppression of GnRH-induced FSH release by 3 alpha HP was only partial if the start of the 3 alpha HP pulse occurred 0.5 or 1.0 min after the start of the GnRH pulse, and no suppression occurred if the start of the 3 alpha HP pulse was delayed by 2-5 min. The FSH release elicited by 5-min pulses of the Ca2+ ionophore A23187, the Ca2+ agonist BAY K8644, the PKC activator phorbol 12-myristate 13-acetate (PMA), or phospholipase C (PLC) was suppressed by simultaneous pulses of 3 alpha HP. The suppression of FSH release by 3 alpha HP appeared to be stereospecific, since no suppression was observed with 5 alpha-pregnane-3,20-dione (5 alpha P) or 3 alpha-hydroxy-5 alpha-pregnan-20-one (5 alpha P3 alpha). In separate experiments, cells were treated with pulses of BSA conjugates of 3 alpha HP, 3 beta HP, or progesterone; the 3 alpha HP-BSA, but not the 3 beta HP-BSA or the progesterone-BSA, suppressed the GnRH-induced release of FSH. The results of this study provide the first evidence that 3 alpha HP exerts immediate (nongenomic) and direct effects on GnRH-induced FSH release by interacting at the level of the pituitary gonadotroph membrane and the phosphoinositol cell signaling cascade involving Ca2+.

Progesterone metabolism by guinea pig intrauterine tissues

Progesterone metabolism by guinea pig amnion, chorion, myometrium, and endometrium was studied at the following gestational stages. Day 45 represents mid-gestation, about 5 days before strong chorion interaction between the entire surface of the chorion and the uterus; days 57-58, 1-2 days after chorion attachment, and 2-3 days before the onset of pubic symphysis relaxation; days +1-+6, 1-6 days after the onset of pubic symphysis relaxation, i.e. within 1 week of parturition. The high metabolic activity of chorion exceeded that by amnion at all stages. Metabolism by endometrium and myometrium was always low. Conversion of progesterone by amnion significantly decreased (P < 0.05) between days 57-58 and days +1-+6. Progesterone metabolites produced by chorion and amnion were identified by TLC, HPLC, and capillary GC/MS. Both tissues converted progesterone to three major products during 60-min incubations. These were 5 alpha-pregnane-3,20-dione, 3 alpha-hydroxy-5 alpha-pregnan-20-one, and 3 beta-hydroxy-5 alpha-pregnan-20-one. The metabolite pattern differed between the two tissues. Three-minute incubations with chorion resulted in a significantly higher proportion of 3 alpha-hydroxy-4-pregnen-20-one (P < 0.01) and 5 alpha-pregnane-3,20-dione (P < 0.025) than at 60 min. The production of 3 beta-hydroxy-5 alpha-pregnen-20-one by chorion decreased (P < 0.05) between days 50-51 and 57-58. The ratio of 3 alpha-hydroxy-5 alpha-pregnan-20-one to 3 beta-hydroxy-5 alpha-pregnan-20-one increased (P < 0.05) between days 45 post-relaxation. The marked conversion of progesterone by chorion, or the formation of one or more of its metabolites, may serve to influence uterine function prior to delivery.

Male preference for the odors of estrous female mice is enhanced by the neurosteroid 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP)

The effects of the centrally produced allylic neurosteroid, 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP), on the responses of male mice to the odors of estrous female mice were examined in an odor preference test. Control untreated mice displayed a significant preference for the odors of an estrous female, spending more time in a Y-maze in the vicinity of the odors of an estrous than a non-estrous female. Intracerebroventricular (i.c.v.) administrations of 3 alpha HP enhanced male preference for the odors of estrous females, causing a significant dose-related (0.01-1.0 microgram) increase in the amount of time spent in the proximity of the odors of the estrous female, while having no significant effect on the responses to the non-estrous female odors. These effects of 3 alpha HP were stereospecific, with the stereoisomer, 3 beta-hydroxy-4-pregnen-20-one (3 beta HP), having no significant effects on odor preferences. The analgesic, morphine, also had no significant effects on the responses to female odors suggesting that the enhanced preference for estrous female odors were unlikely to be directly due to any analgesic effects of 3 alpha HP. The effects of 3 alpha HP were significantly reduced by peripheral administrations of the GABAA antagonists, bicuculline and picrotoxin, but were unaffected by either the benzodiazepine antagonist, Ro 15-1788, or the opiate antagonist, naloxone. These results suggest that the neurosteroid 3 alpha HP has facilitatory effects on olfactory mediated male sexual interest or motivation that involve interactions with the GABAA receptor.

Reduction of predator odor-induced anxiety in mice by the neurosteroid 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP)

The effects of the centrally produced allylic neurosteroid, 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP), on the responses of male mice to an aversive, anxiety-inducing, predator (cat) odor were examined in an odor preference test. Control untreated mice displayed an anxiogenic response to the cat odor, spending a minimal amount of time in a Y-maze in the vicinity of the cat odor. Intracerebroventricular (i.c.v.) administrations of 3 alpha HP had an anxiolytic action, resulting in significant dose-related (0.01-1.0 micrograms) increases in the amount of time spent in the proximity of the cat odor. These anxiolytic effects of 3 alpha HP were stereospecific, with the stereoisomer, 3 beta-hydroxy-4-pregnen-20-one (3 beta HP) having no significant effects on odor preferences. The analgesic, morphine, also had no significant effects on the response to cat odor indicating that the anxiolytic actions of 3 alpha HP were unlikely to be related to any analgesic effects. The effects of 3 alpha HP were significantly reduced by peripheral administrations of the GABAA antagonists, bicuculline and picrotoxin, but were unaffected by either the benzodiazepine antagonist, Ro 15-1788, or the opiate antagonist, naloxone. These results indicate that the allylic neurosteroid 3 alpha HP has anxiolytic actions involving interactions with the GABAA receptor.

Perispinal progestins enhance the antinociceptive effects of muscimol in the rat

The intrathecal (IT) injection of progesterone (PROG) or three of its ring A-reduced metabolites (5 beta,3 alpha-pregnanolone, 5 alpha,3 alpha-pregnanolone, or 5 beta,3 beta-pregnanolone) did not significantly alter any of two pain thresholds (vocalization threshold to tail shock, VTTS, or tail flick latency, TFL) in ovariectomized rats when tested in a wide range of doses (2.5-250 micrograms). When combined with a subanalgesic dose of muscimol (MUSC; 1 microgram IT), PROG and its two 3 alpha-hydroxy derivatives, but not the 3 beta, caused significant analgesia in the VTTS but not in the TFL test. No clear dose-response relationships were noted in the analgesic response to the combination of the progestins and MUSC. The present results indicate that PROG, either directly or through its ring A-reduction, can modulate nociceptive information by enhancing the action of GABA agonists on GABAA receptors.

A radioimmunoassay for the regulatory allylic steroid, 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP)

The allylic steroid, 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP), found in gonadal and brain tissues by radiotracer and chemical methods, had been shown to play a role in gametogenesis, gonadotropin secretion and brain excitability. Since no simple assay was available, a radioimmunoassay for 3 alpha HP was developed using [3H]3 alpha HP and an antiserum raised against 3 alpha HP-20-CMO conjugated to bovine serum albumin. The specificity of the assay for the 3 alpha allylic configuration of 3 alpha HP was confirmed by examining 32 other steroids; cross-reaction with steroids containing different configurations (including metabolites of 3 alpha HP such as progesterone) was less than 0.9%. A Scatchard plot indicated a Ka of 1.56 X 10(9) M-1. Inter- and intra-assay coefficients of variation were 13.1 and 4.5%, respectively. The sensitivity of the assay was 6 pg and the 50% intercept of the standard curve was approx. 123 pg. The measurement by RIA of 3 alpha HP from standard solutions and HPLC purified tissue extracts was confirmed qualitatively and quantitatively by GC/MS methods. The RIA method was employed to determine 3 alpha HP levels in cultured Sertoli cells and in serum of intact and ovariectomized adult rats. Although for most uses, chromatography would not be necessary, two possible methods are presented to enable the separation of 3 alpha HP from other interfering steroids prior to RIA.

Metabolism of progesterone by avian granulosa cells in culture

Previous studies have demonstrated that progesterone is the primary product of steroidogenesis in avian granulosa cells during short-term incubation. However, during more prolonged culture, lasting several days, the progesterone content in the medium was found to decrease progressively, indicating in vitro metabolic conversion. In the present study we have isolated and identified a number of progesterone metabolites. Granulosa cells, isolated from mature ovarian follicles of laying hens, were cultured in medium 199 supplemented with fetal calf serum and containing [14C]progesterone. After 4 days in culture, cells + media were extracted and the radioactive metabolites separated and identified by TLC, HPLC and GC-MS. Several of the metabolites were further characterized by derivatization and crystallization to constant specific activity. A total of 24 radioactive substances was detected. Of these, 15 have been positively identified, 5 tentatively and the remaining 4 are unidentified. The principal metabolite, representing more than 45% of the total radioactivity, was identified as 3 alpha-hydroxy-5 beta-pregnan-20-one. In addition, significant amounts of 3 alpha-hydroxy-5 alpha-pregnan-20-one (5.76%), 5 beta-pregnane-3,20-dione (3.05%), and 5 alpha-pregnane-3,20-dione (2.95%) were detected and identified. The results indicate that avian granulosa cells possess 3 alpha-hydroxy-steroid dehydrogenase (3 alpha-HSD), 17 beta-HSD, 20 alpha-HSD, 20 beta-HSD, 17 alpha-hydroxylase, C17-20-lyase and 5 alpha- and 5 beta-reductase activities. These enzyme activities may convert progesterone to biologically inactive or less active metabolites. However, a functional role for some of these metabolites cannot be ruled out.