Hypothalamic Aromatase Research Articles

Altered brain and pituitary androgen metabolism by prenatal, perinatal or pre- and postnatal finasteride, flutamide or dihydrotestosterone treatment in juvenile male rats

Lephart Edwin D. and Douglas A. Husmann: Altered brain and pituitary androgen metabolism by prenatal, perinatal or pre- and postnatal finasteride, flutamide or dihydrotestosterone treatment in juvenile male rats. Prog. Neuro-Psychopharmacol. & Biol. Psychiat. 1993, 17(6): 991–1003. 1. 1. The authors investigated the administration of finasteride, a 5α-reductase inhibitor; flutamide, an androgen receptor blocker and; exogenous dihydrotestosterone (DHT) during intervals covering different portions of the “critical period” of neural development ( i.e. prenatal, perinatal or pre- and postnatal development) to determine the long-term effects of these agents on altering androgen metabolism in hypothalamic and pituitary tissue of juvenile (30 day-old) male rats. 2. 2. The efficacy of the treatments and hypothalamic-pituitary axis function was monitored by measuring luteinizing hormone levels by radioimmunoassay. 5α-Reductase and aromatase activity was determined in hypothalamic and pituitary tissue. 3. 3. Significant alterations in pituitary 5α-reductase activity was detected in DHT-treated animals, whereas, hypothalamic 5α-reductase activity was significantly decreased by finasteride treatment and significantly increased by DHT treatment. Hypothalamic aromatase activity was significantly decreased in flutamide-treated animals. 4. 4. These results suggest that: a) prenatal exposure to exogenous DHT stimulates hypothalamic (but inhibits pituitary) 5α-reductase activity long-term and b) basal 5α-reductase activity levels can be inhibited by finasteride treatment in hypothalamic but not in pituitary tissue, suggesting that a different regulatory mechanism exists for 5α-reductase in hypothalamic verses pituitary tissue.

In vitro potency and selectivity of the non-steroidal androgen aromatase inhibitor CGS 16949A compared to steroidal inhibitors in the brain

A sensitive in vitro 3H 2O microassay for aromatase activity was used to evaluate the potency and selectivity of three aromatase inhibitors in mammalian (gerbil) and avian (ring dove) hypothalamus. The steroidal inhibitors, 1,4,6-androstatrien-3,17-dione (ATD) and 4-hydroxy-androstenedione (4-OH-A) were compared with a new non-steroidal imidazole inhibitor, CGS 16949A [4-(5,6,7,8-tetrahydroimidazo-[1,5-a]-pyridin-5-yl)benzonitrile HCl]. Adult male dove hypothalamic aromatase is highly active [ V max = 5.3 pmol testosterone (T) converted/h/mg pprotein], has high substrate binding affinity ( K m = 4.0 nM), and direct involvement in control of sexual behaviour. With [1β- 3H]T or [1β- 3H]A as substrate, male dove preoptic aromatase activity was inhibited more effectively and selectively by CGS 16949A. Thus, K i s and IC 50s for aromatization were ∼50 times lower for the non-steroidal inhibitor, and inhibition of the other major androgen-metabolizing enzymes (5α/β-reductase) occured at concentrations at least one order of magnitude greater than for ATD and 4-OH-A. Neonatal male gerbil hypothalamic aromatase activity ( V max = 1.3 pmol T converted/h/mg protein) was lower than in the dove. Aromatase inhibition by CGS 16949A is more potent in the neonatal gerbil than in the dove ( K i s of 0.03 and 0.06 nM, respectively, with A as substrate). We conclude that the imidazole is an effective aromatase inhibitor in both the adult and developing brain.

Effects of Cyclic AMP and Andre-gens on in vitro Brain Aromatase Enzyme Activity During Prenatal Development in the Rat

In the rat, there is a marked but transient increase in hypothalamic aromatase activity during the last week of fetal life. The present study was undertaken to gain insight into the regulation of this developmental pattern. Hypothalamic fragments comprising the medial basal hypothalamus and the suprachiasmatic region (henceforth referred to as preoptic area) were explanted and cultured in serum-free medium for 2 to 5 days. Aromatase activity was measured by the formation of (3) H(2) O, utilizing either [1ß-(3) H]androstene-dione or [1ß-(3) H]testosterone as substrate. Maximal rates of activity were obtained at a saturating concentration of 0.3 μM [1ß-(3) H]testosterone. Confirmation of the identity of the [(3) H]estradiol formed was demonstrated by recrystallization of the derivatized estradiol to constant specific activity following incubation with [1,2,6,7-(3) H]testosterone. In agreement with previous reports, in vivo hypothalamic aromatase activity was negligible before gestational day (GD) 16, increased strikingly by GD19 (>5.0 pmol/h/mg protein) and decreased, thereafter, to low levels at GD22 (∼1.0 pmol/h/mg protein). Medial basal hypothalamus-preoptic area fragments explanted before GD17 failed to develop aromatase activity in vitro. If the tissue was explanted on GD17 or 18 (i.e. when the in vivo rate of activity was increasing), the enzyme activity did not continue to increase, but it was rather maintained for 2 days before decreasing in a manner that closely mimicked the decline observed in vivo. A similar, butimmediate decline was observed when the tissue was explanted on GD19 (i.e. at the time when theactivity peaks in vivo). Exposure of explants to either growth factors (insulin-like growth factor II, epidermal growth factor, and basic or acidic fibroblast growth factor), or steroids (estradiol-17ß, progesterone, testosterone, dihydrotestosterone and corticosterone) failed to either increase aromatase activity before the peak at GD19 or ameliorate its perinatal decline. Increase of Ca(2+) fluxes with the ionophore A23187 or activation of the cyclic AMP, cyclic GMP, or protein kinase C pathways were similarly ineffective, as was angiotensin II, a recently proposed stimulator of neural aromatase. In contrast, aromatase activity was suppressed 2- to 4-fold by activation of the cyclic AMP pathway (with either forskolin or 8-bromo-cyclic AMP) or by the androgens, testosterone and dihydrotestosterone. These results suggest that: 1) the appearance of aromatase activity in the rat hypothalamus before GD17 requires the unfolding of extrahypothalamic events, 2) the increase in aromatase activity that occurs before GD19 also requires extrahypothalamic inputs and does not involve any of the known intracellular signal transduction pathways, and 3) the decline in activity observed after GD19 is regulated within the hypothalamus, and appears to be determined, at least in part, by the activation of cyclic AMP formation. A potential role for androgens is discussed.

Inhibition of Hypothalamic Aromatase Activity by 5 Beta‐Dihydrotestosterone

Abstract A variable amount of circulating testosterone that reaches brain cells is converted to biologically inactive 5beta-reduced metabolites, namely, 5beta-dihydrotestosterone (5beta-DHT) and 5beta-androstane-3alpha,17beta-diol (5beta,3alpha-diol). In avian species, the production of inactive 5beta-DHT and 5beta,3alpha-diol is highest during embryonic and post-hatching life. In the present study, we have investigated the possibility that 5beta-reduction may not only correspond to a steroid inactivation pathway, but that 5beta-reduced metabolites of testosterone may exert direct inhibitory effects on enzymatic pathways producing biologically active steroids. When added to hypothalamic homogen-ates prepared from adult male doves, 5beta-DHT but not 5beta,3alpha-diol inhibits the activity of the aromatase enzyme, which converts testosterone to 17beta-oestradiol. During the first days after hatching, when the production of 5beta-reduced metabolites is high, the hypothalamic aromatase is also inhibited by 5beta-DHT. We conclude that a high 5beta-reductase activity during sensitive periods for sexual differentiation may protect the avian brain from the differentiating effects of circulating androgens by inhibiting the production of oestrogen.

Effects of the nonsteroidal inhibitor R76713 on testosterone-induced sexual behavior in the Japanese quail ( Coturnix coturnix japonica)

A new triazole derivative, R76713 (6-[(4-chlorophenyl)(1 H-1,2,4-triazol-1-yl)methyl]-1-methyl-1 H-benzotriazole), was recently shown to inhibit aromatase selectively without affecting other steroid-metabolizing enzymes and without interacting with estrogen, progestin, or androgen receptors. This compound was tested for its capacity to intefere with the induction of copulatory behavior by testosterone (T) in castrated Japanese quail ( Coturnix coturnix japonica). In a first experiment, R76713 inhibited (range 0.01 to 1 mg/kg) the activation of sexual behavior by T silastic implants and hypothalamic aromatase activity in castrated male quail in a dose-dependent manner. The 5α- and 5β- reductases of T were not systematically affected. Stereotaxic implantation of R76713 in the medial preoptic area similarly blocked the behavior activated by systemic treatment with T, demonstrating that central aromatization of androgen is implicated in the activation of behavior. These inhibiting effects of R76713 on behavior were observed when implants were placed in the medial part of the nucleus preopticus medialis, confirming the implication of this brain area in the control of male copulatory behavior. Finally, the behavioral inhibition produced by R76713 could be reversed by simultaneous treatment with a dose of estradiol, which was not behaviorally effective by itself. This suggests that the behavioral deficit induced by the inhibitor was specifically due to the suppression of estrogen production. This also shows that the activation of copulatory behavior probably results from the interaction of androgens and estrogens at the brain level, as the two treatments separately providing these hormonal stimuli (T with the aromatase inhibitor on one hand and a low dose of estradiol on the other hand) had almost no behavioral effects but they synergized to activate copulation when given concurrently. These data confirm the critical role of preoptic aromatase in the activation of reproductive behavior and demonstrate that R76713 is a useful tool for the in vivo study of estrogen-dependent processes.

Hypothalamic Aromatase Activity in Male and Female Rats during Juvenile Peripubertal Development

Evidence exists that testosterone (T) regulates brain aromatase activity in adult rats. It is not known, however, whether the activity and/or its regulation by androgens change during the time of puberty. In the present study, we examined the change in basal aromatase activity associated with puberty in both male and female rats. We also assessed the influence of castration and treatment with a nonaromatizable androgen, dihydrotestosterone (DHT), on the hypothalamic aromatase system during juvenile and peripubertal development of male rats. Aromatase activity was estimated by both quantifying the 3H2O released from [1 beta-3H]T and by isolating the estrogen product(s) by thin-layer chromatography (TLC) after incubations with [1,2,6,7-3H]T. 5 alpha-Reductase activity was determined simultaneously in the male hypothalamus by TLC using [1 alpha-3H]T as the substrate. Aromatase activity was linear with time of incubation and amount of tissue used. It was detected at similar levels in both tissue fragments and acutely dispersed cell preparations. Expression in the latter, but not the former required the addition of NADPH. Intracellular rates of both aromatase and 5 alpha-reductase activities were highest in the mitochondrial-microsomal fraction. In both males and females the time of puberty was associated with a decrease in hypothalamic aromatase activity. In females, this drop was found to occur between the days of first proestrus and first estrus. In males, it occurred between 48 and 68 days of age (i.e., after the animals had reached puberty, as assessed by the presence of free sperm in the seminiferous tubules).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of in utero treatment with 4-hydroxy-androstenedione on hypothalamic aromatase activity and differentiation of sexually dimorphic behavior in rat

Effects of in utero treatment with 4-hydroxy-androstenedione on hypothalamic aromatase activity and differentiation of sexually dimorphic behavior in rat

Perinatal aromatase activity in male and female rats: effect of prenatal alcohol exposure.

Fetal alcohol exposure has been shown to produce long-term feminizing and demasculinizing effects on male rat behaviors which are organizationally dependent upon perinatal androgen levels. Such exposure has previously been shown to suppress the normal surge of testosterone during the critical prenatal period. Since defeminization of male rat behavior is dependent upon estrogen derived from the aromatization of testosterone in brain, brain aromatase activity was measured during the perinatal period in males and females exposed to alcohol beginning on Day 14 of gestation. Aromatase activity was measured in whole hypothalamus of fetuses from Day 16 through 20 of gestation and in the hypothalamic preoptic area and amygdala of animals 6-12 hr postparturition. Hypothalamic aromatase activity was elevated in fetal alcohol exposed males compared to controls on Days 18 and 19 of gestation and on postnatal Day 1. No effect of prenatal alcohol exposure was found in females. A sex effect in aromatase activity in the amygdala was evident on Day 1 when activity was found to be greater in males than females. Overall, these findings indicate that fetal alcohol exposure will elevate regional brain aromatase activity in males, but not females during the perinatal period of neurobehavioral sexual differentiation.

Ontogeny of testosterone-inducible brain aromatose activity

The effects of testosterone (T) treatment on androgen-metabolizing enzymes and especially on aromatase were examined in the developing hypothalamus of quail using an in vitro microassay. Testosterone propionate (TP) injected into the pectoral muscles of one-day-old chicks had no effect on formation of 5α-dihydrotestosterone (5α-DHT), 5β-dihydrotestosterone (5β-DHT) and 5β-androstane-3α,17β-diol (5β,3α-diol) in the hypothalamus. By contrast, aromatase activity was significantly enhanced in the anterior (PA) and in the posterior (HT) parts of the hypothalamus of these chicks 18–23 h after a single injection of TP. This increase was site specific as it did not occur in control non-target areas, neostriatum intermediate and hyperstriatum ventrale (VN). The increase in hypothalamic aromatase activity was accompanied by T-dependent changes in behavior and somatic development. Although aromatase activity is present as early as day 10 of embryonic life in PA and HT, it becomes inducible by circulating T only after this stage of development. There is also an important increase in basal aromatase activity during embryonic development. At day 10, when the brain is particularly sensitive to the differentiating effects of gonadal steroids, formation of 5α-DHT and 5β-DHT in the hypothalamus is higher in females than in males. We conclude that although all important pathways of T are already present on day 10 of embryonic life, the brain metabolism of androgens continues maturing during the whole embryonic life.

Studies on the role of catecholamines in the regulation of the developmental pattern of hypothalamic aromatase.

Experiments were conducted to study the regulation of the developmental pattern of aromatase in the forebrain of the perinatal rat. Two experimental designs were used: aromatase measured in primary cultures of fetal hypothalamic cells and in cell-free preparations of forebrain tissue excised at varying ages. In cultured cells, aromatase decreased logarithmically at a slow rate (t1/2 = 7.8 days). Norepinephrine caused a pronounced dose (4 x 10(-6) M) and time-dependent (2-6 days) drop in aromatase without affecting the levels of 5 alpha-reductase or substance P. In isolated tissue, aromatase activity was compared with the concentrations of norepinephrine and dopamine in the forebrain of males vs females at different perinatal ages and in discrete forebrain areas at postnatal day 4. In no case was a sex difference in catecholamines seen. An overall developmental decline in aromatase was associated with developmental increases in catecholamine levels. Acute treatment with the beta-agonist, isoproterenol, had no effect on brain aromatase activity.

Effect of progesterone on the testosterone and estradiol levels in the hypothalamus of neonatal rats.

Pregnant female rats were injected with progesterone or oil from 18.5 up to 21.5 days of gestation. Rat pups were delivered by caesarean section, and pups delivered from progesterone-treated mothers were injected with 100 micrograms of progesterone and pups from oil-treated mothers were injected with oil. Two hours after delivery, pups were killed and hypothalamic testosterone and estradiol were determined by RIA. Control males had substantially higher concentrations of testosterone and estradiol in hypothalamus than control females. Treatment with progesterone did not affect the accumulation of testosterone in the hypothalamic tissue of neonatal males, but completely prevented the formation of estradiol in hypothalamic tissue. This result suggests that progesterone can inhibit hypothalamic aromatase activity in the neonate and may explain why progesterone can protect against some of the neural defeminizing effects of neonatally administered androgens.

Testosterone induces hypothalamic aromatase during early development in quail

The effects of testosterone on androgen metabolizing enzymes were examined in the developing hypothalamus of male and female quail using an in vitro radiometric assay which measures metabolite formation in individual brain samples. Testosterone (T) administered by subcutaneous silastic implants to gonadectomized 4-day-old chicks increased formation of estradiol-17β (E2) in both preoptic area + anterior hypothalamus (PA) and posterior hypothalamus + tuberal area (HT) to adult levels. The T-induced increase in E2 formation occurred to the same degree in both sexes. The increase was very small in control non-target areas, neostriatum intermediale + hyperstriatum ventrale (VN), of either sex. Testosterone had no effect on formation of 5α-dihydrotestosterone (5α-DHT), 5β-dihydrotestosterone (5β-DHT) and 5β-androstane 3α,17β-diol (5β,3α-diol) in PA. Kinetic analysis of the rate of E2 production by hypothalamic tissue from castrated chicks (CX-chicks) and castrates treated with T (CX+T-chicks) indicates that the increase in hypothalamic aromatase activity by T corresponds to induction of the enzyme: the V max (maximum velocity) was increased by T (CX-chicks, 21; CX+T-chicks, 91 fmol/mg FW/h), whereas the K m was unaffected (CX-chicks, 5.5; CX+T-chicks, 4.7 × 10 −8 M). Testosterone treatment, effective for inducing PA and HT aromatase activity, also activated crowing and caused cloacal gland development; neither of these effects were sexually dimorphic. Our results indicate that: (1) T induces aromatase specifically in the hypothalamus during early post-hatching development, other pathways of T metabolism are not affected; and (2) the inducible aromatase is not sexually dimorphic in the developing brain. Since there are sex differences in adult brain aromatase, we conclude that capacity for induction of the hypothalamic aromatase becomes sexually differentiated after the post-hatching period.

Testosterone-induced brain aromatase is sexually dimorphic

Female quail are less sensitive than males to the activating effects of testosterone (T) on behavior. Testosterone induces hypothalamic aromatase activity more efficiently in males than in females (higher V max but similar K m). As the conversion of T to estradiol (E 2) is important for the activation of male sexual behavior, we propose that the incapacity of the female hypothalamus to produce behaviorally active E 2 contributes to their insensitivity to T. The 5α-reductase, which converts T into 5α-dihydrotestosterone (5α-DHT), is induced by T specifically in the anterior hypothalamus of both sexes.

Hypothalamic aromatase activity in young and old male rats

We studied the capability of hypothalamic tissue from young (3–4 months) and old (22–24 months) male rats to aromatize androgens to estrogens. Aromatase activity was measured in homogenates of brain tissue by using a radiometric assay that quantifies the stereospecific production of 3H 2O from [1β- 3H]androstenedione as an index of estrogen formation. Despite the 40% drop in circulating testosterone (T) levels associated with aging in males, we found that hypothalamic aromatase activity was unaffected by age. This finding suggested that chronic exposure to low levels of circulating T can maintain brain aromatase activity in aged male rats. In an experiment designed to examine the acute response of hypothalamic aromatase activity to induction by T, we found a significant positive correlation between circulating T levels and hypothalamic aromatase activity in both age groups. These results demonstrate that T remains an effective regulator of hypothalamic aromatase in old male rats.

Development of testosterone-metabolizing pathways in the avian brain: Enzyme localization and characteristics

Metabolites formed from testosterone in the brain, their neuroanatomical distribution and the kinetic properties of the enzymes were studied in male and female Japanese quail chicks and compared with the adult brain using an in vitro radioassay. Oestradiol-17β, 5α-dihydrotestosterone, 5β-dihydrotestosterone and 5β-androstane-3α,17β-diol were identified as metabolites of testosterone (T) in hypothalamic samples of 3-day-old quail. Estimation of the K m of hypothalamic aromatase (4.8 × 10 −8 M) and 5α-reductase (11.8 × 10 −8 M) suggests that the affinities of the enzymes for substrate (T) are similar to those of comparable adult brain enzymes. Formation of 5α-dihydrotestosterone and oestradiol-17β was higher in the preoptic area and posterior hypothalamus than either the area basalis or neostriatum intermediale, whereas 5β-dihydrotestosterone yield did not differ between brain areas. Similar regional differences in testosterone metabolism were confirmed developing dove brain (2–8-day-old chicks). In both quail and dove, the activities of hypothalamic aromatase and 5α-reductase were lower in the chick brain than in the adult, but brain 5β-reductase activity was much higher during early development than in adulthood. We conclude that the major pathways of testosterone metabolism in the brain are active during early development. Concentrations of enzymes and relative differences in enzyme activity between brain areas change substantially during development.

The Regulation System of Brain Aromatase Activity

Recently, some studies have found the greatest aromatase activity in brain areas associated with sexual differention and sexual behavior, namely the hypothalamic and limbic structures. We studied the regulation of aromatase activity in the hypothalamic area of male rats, using a sensitive in vitro assay which measures the amount of 3H2O formed by tissue homogenates during the conversion of [1 beta-3H] androstenedione to estrogen. After castration, hypothalamic aromatase activity was significantly decreased (P less than 0.01), and seminal vesicle (SV) and prostate (PR) weights were also significantly decreased (P less than 0.01). Castrated male rats were given testosterone (T), 5 alpha-dihydrotestosterone (DHT), 5 alpha-androstane-3 alpha, 17 beta-diol (A3 alpha), 5 alpha-androstane-3 beta and 17 beta-diol(A3 beta) in various doses (200-1000 micrograms/day) for 10 days, and were given 600 micrograms/day T, DHT, A3 alpha and A3 beta for various durations (1-10 days). We found that T, DHT and A3 alpha but not A3 beta reversed the effects of castration on the hypothalamic aromatase activity. The order of this reversible effect of androgens was as follows: T greater than or equal to DHT greater than A3 alpha. T, DHT, A3 alpha and A3 beta increased SV and PR weights, and the order of this effect was as follows: DHT greater than T greater than A3 alpha much greater than A3 beta. We administered the antiandrogen (flutamide) to intact male rats (8 mg/day for 6 days). Flutamide decreased hypothalamic aromatase activity at the same level as that of castrated rats. Likewise, administration of both flutamide and T to castrated rats blocked the T-induced increase in hypothalamic aromatase activity and accessory sexual organ weight. From these results, we suggest that T, DHT and A3 alpha regulated hypothalamic aromatase activity, that T was the most effective of the androgens, and that was different from peripheral androgen target organs.

Changes in aromatase activity in the neuroendocrine tissues of red grouse (Lagopus lagopus scoticus) in relation to the development of long-day refractoriness.

Changes in aromatase activity in the neuroendocrine tissues of captive male and female red grouse (Lagopus lagopus scoticus) were measured during a photo-induced breeding cycle. The gonads enlarged and subsequently regressed, as a consequence of the development of long-day refractoriness, within 84 days of transferring photoinsensitive birds from a non-stimulatory to a stimulatory daylength. The object of the study was to determine whether long-day refractoriness is related to an increase in aromatase activity in the neuroendocrine tissues which might result in a greater inhibitory action of locally produced oestrogens on the release of LH-releasing hormone. Aromatase activity was measured and found to be present in the anterior pituitary gland, the anterior/preoptic hypothalamus, the posterior hypothalamus and the hyperstriatum dorsale. It was higher in the hypothalamus than in the hyperstriatum dorsale and higher in the posterior than in the anterior/preoptic hypothalamus. Aromatase activity in the posterior hypothalamus was higher in males than in females in short-day photosensitive and reproductively active birds, but not in long-day refractory birds. A similar sex difference was also observed in the anterior/preoptic hypothalamus in reproductively active birds. Hypothalamic aromatase activity in both sexes was directly related to gonadal function, being highest in reproductively active birds and lowest in long-day refractory birds. It is concluded that the development of long-day refractoriness is not related to an increase in aromatase activity in the neuroendocrine tissues. The decrease in aromatase activity in the neuroendocrine tissues in long-day refractory birds parallels a decrease in aggressive and territorial behaviour.

The effects of the aromatase inhibitor delta 1-testolactone on gonadotropin release and steroid metabolism in polycystic ovarian disease.

This study was designed to examine the importance of aromatization in the gonadotropin secretory dynamics of polycystic ovarian disease (PCOD) by using the aromatase inhibitor delta 1 testolactone (TL) as a probe and to determine the effects of TL on steroid metabolism in vivo and in vitro. The pulsatile patterns of gonadotropin secretion and peripheral steroid levels were studied in eight women with PCOD before and during TL administration. There was a significant fall in peripheral estrone (E1) levels, a rise in peripheral androstenedione levels, and an increase in the androstenedione/E1 ratio during TL administration in these women. Isotopic determinations of androgen and estrogen production and metabolism before and during TL administration in two women confirmed a 90-95% decrease in the overall rate of aromatization. One patient also had an increase in the production and clearance rates of estradiol and E1 during TL administration, suggesting resistance to TL of the ovarian aromatase enzyme system. There were significant increases in both mean LH pulse amplitude [1.2 +/- 0.3 (SE) mIU/ml LER-907 before vs. 1.7 +/- 0.3 mIU/ml LER-907 during TL, P less than 0.05, paired t test] and frequency per 6 h (median: 3 before vs. 4 during TL, P less than 0.05, Wilcoxon signed rank test). Mean levels of LH and FSH did not, however, change significantly during TL administration. TL maximally inhibited neonatal rat hypothalamic aromatase in vitro at concentrations of 200 microM, a level theoretically obtainable during pharmacological therapy. These data suggest that: 1) in humans TL is a potent inhibitor of peripheral but not ovarian aromatase, and of hypothalamic aromatase in rats; 2) TL administration increases LH pulse amplitude and frequency in PCOD, either directly via hypothalamic aromatase inhibition, or indirectly by alterations in gonadal steroid metabolism; and 3) because of the multiple potential actions of TL, its usefulness as a probe in studies of gonadotropin secretion in PCOD is limited.

Inhibition of aromatization stimulates luteinizing hormone and testosterone secretion in adult male rhesus monkeys.

Experiments were conducted to examine the role of aromatization in the control of LH and testosterone secretion in adult male rhesus monkeys. Treatment of male monkeys (n = 7) with sc Silastic packets containing the aromatase inhibitor 1,4,6-androstatriene-3,17-dione (ATD) resulted in 1.5- to 3-fold elevations in serum LH and testosterone concentrations in six of seven animals. Concurrent treatment of ATD-treated monkeys with small quantities of estradiol-17 beta (n = 4) abolished the stimulatory effect of ATD. During ATD treatment, peripheral estradiol levels were reduced by 30% and hypothalamic aromatase activity, as determined in vitro, was reduced 80-90%. The lack of androgenic or antiandrogenic activity of ATD was demonstrated by its inactivity in either a mouse seminal vesicle bioassay or a highly sensitive penile spine bioassay. Furthermore, ATD did not react with rat prostatic or hypothalamic cytosol androgen receptors. 1,4,6-Androstatriene-17-ol-3-one, a possible metabolite of ATD in vivo, did react with prostatic and hypothalamic androgen receptors, but possessed no antiandrogenic activity in either bioassay. Thus, treatment of adult males with an aromatase inhibitor that inhibits both peripheral and central aromatization, and which has no apparent antiandrogenic activity, results in stimulation of LH and testosterone secretion. These data demonstrate that aromatization of androgens to estrogens plays an important role in negative feedback regulation of LH secretion and maintenance of normal testosterone levels in adult male primates.

Cyclophenil, a non-steroidal compound with a higher central than peripheral oestrogenic activity: study of its effects on uterine growth and on some central parameters in castrated female rats.

The oestrogenic activity of cyclophenil, a non-steroidal compound which has structural analogies with both stilbene and triphenylethylene, has been reevaluated utilizing both central and peripheral parameters. The central parameters considered were LH, FSH, prolactin secretion and two enzymatic systems known to be oestrogen-sensitive: hypophyseal 5alpha-reductase and hypothalamic aromatase. The uterine growth test was used to determine oestrogenic peripheral activity. The compound was administered at various doses in comparison with oestradiol benzoate (EB) to long-term castrated female rats. Cyclophenil has an activity 1/8110 times that of EB on uterine growth, and 1/1660 and 1/550 times that of EB in inhibiting LH and FSH, respectively. The hypophyseal 5 alpha-reductase (expressed as DHT formation) was inhibited 1710 times less by cyclophenil than by EB. The other parameters considered were unsuitable to provide a statistically reliable estimate of the potency ratios between the two compounds. The data show that cyclophenil is an oestrogenic compound with peculiar characteristics. This substance is more effective in expressing its oestrogenic activity in central structures than in the peripheral ones.