Differential nuclear binding of [3H]testosterone and its metabolites to androgen and estrogen receptors in brain, pituitary, heart, kidney and accessory sex glands of the mouse: an autoradiographic study

Testosterone metabolites mediate its effects on myocardial damage induced by ischemia/reperfusion in male Wistar rats

The role of testosterone in cardiovascular (CV) homeostasis is in controversy, and the exact effects of testosterone on the cardiovascular system remain poorly understood. Testosterone is metabolized by aromatase into 17β-estradiol and by 5α-reductase into dihydrotestosterone (DHT). Thus, identification of these metabolites in the heart may help to explain the controversy regarding the cardiovascular effects of testosterone. We analyzed the expression patterns of these testosterone-metabolizing enzymes and assessed the effect of its enzymatic activity inhibition on ischemia (40 min)/reperfusion (4h, I/R) via the left anterior descendent coronary artery in intact and gonadectomized male rats. Myocardial damage was measured as percentage of infarcted area vs. area at risk. Aromatase and 5α-reductase protein expression was found in the left ventricle of intact and orchidectomized rats. Exogenous testosterone had no effect on I/R induced myocardial damage in intact male rats, meanwhile exogenous testosterone protects against I/R injury in orchidectomized rats. However, enzymatic inhibition of aromatase increased myocardial damage in the presence of testosterone, while enzymatic inhibition of 5α-reductase significantly decreased the level of myocardial damage. Our results also showed that sub-chronic inhibition of 5α-reductase resulted in myocardial protection in both groups. Furthermore, in orchidectomized and intact male rats IV treatment with DHT induces a significant increase in the myocardial damage induced by I/R. Thus, the effect of testosterone on cardiovascular pathophysiology could be related, at least in part to changes in the balance of testosterone 5α-reduction and aromatization.

Facilitation of male sexual behavior in Syrian hamsters by the combined action of dihydrotestosterone and testosterone

Background

Testosterone (T) controls male Syrian hamster sexual behavior, however, neither of T's primary metabolites, dihydrotestosterone (DHT) and estradiol (E₂), even in highly supraphysiological doses, fully restores sexual behavior in castrated hamsters. DHT and T apparently interact with androgen receptors differentially to control male sexual behavior (MSB), but whether these two hormones act synergistically or antagonistically to control MSB has received scant experimental attention and is addressed in the present study.

Methodology/Principal Findings

Sexually experienced male Syrian hamsters were gonadectomized and monitored 5 weeks later to confirm elimination of the ejaculatory reflex (week 0), at which time they received subcutaneous DHT-filled or empty capsules that remained in situ for the duration of the experiment. Daily injections of a physiological dose of 25 µg T or vehicle commenced two weeks after capsule implantation. MSB was tested 2, 4 and 5 weeks after T treatment began. DHT capsules were no more effective than control treatment for long-term restoration of ejaculation. Combined DHT + T treatment, however, restored the ejaculatory reflex more effectively than T alone, as evidenced by more rapid recovery of ejaculatory behavior, shorter ejaculation latencies, and a greater number of ejaculations in 30 minute tests.

Conclusions/Significance

DHT and T administered together restored sexual behavior to pre-castration levels more rapidly than did T alone, whereas DHT and vehicle were largely ineffective. The additive actions of DHT and T on MSB are discussed in relation to different effects of these androgens on androgen receptors in the male hamster brain mating circuit.

The role of nitric oxide in female reproduction

The cardiovascular system undergoes profound changes during pregnancy. Maternal intravascular volume begins to increase in the first trimester rising an average of 45% by term.1Cardiac output increases similarly2and is redistributed to organs whose functions are crucial for a successful pregnancy. In the guinea pig, uterine artery (UA) blood flow increases 3500%, while mesenteric and renal artery blood flows increase only 90% and 10% respectively.3Blood flow to the trunk actually diminishes. The mechanism underlying this redistribution is unknown. Coupled with the rise in cardiac output is a decrease in the systemic pressor response to angiotensin II (AII), norepinephrine(NE), and epinephrine.4–8There is also a decrease in the contraction response among some but not all vascular beds. For example, contraction of UA to NE and thromboxane is characteristically reduced by pregnancy, whereas the response of the carotid artery is unaltered8–10Since pregnancy does not alter neuroeffector mechanisms of NE such as release, receptor sensitivity, and accumulation11, changes in sympathetic control during pregnancy must be dependent on alterations at sites other than the neuroeffector junction. We have hypothesized that the mechanisms which alter vascular reactivity during pregnancy also mediate the redistribution of maternal cardiac output.9We have further hypothesized that many of these mechanisms involve endothelium-dependent factors which are modulated by sex hormones.

FHL2, a novel tissue-specific coactivator of the androgen receptor

The control of target gene expression by nuclear receptors requires the recruitment of multiple cofactors. However, the exact mechanisms by which nuclear receptor-cofactor interactions result in tissue-specific gene regulation are unclear. Here we characterize a novel tissue-specific coactivator for the androgen receptor (AR), which is identical to a previously reported protein FHL2/DRAL with unknown function. In the adult, FHL2 is expressed in the myocardium of the heart and in the epithelial cells of the prostate, where it colocalizes with the AR in the nucleus. FHL2 contains a strong, autonomous transactivation function and binds specifically to the AR in vitro and in vivo. In an agonist- and AF-2-dependent manner FHL2 selectively increases the transcriptional activity of the AR, but not that of any other nuclear receptor. In addition, the transcription of the prostate-specific AR target gene probasin is coactivated by FHL2. Taken together, our data demonstrate that FHL2 is the first LIM-only coactivator of the AR with a unique tissue-specific expression pattern.

Nitric oxide and pregnancy

We have hypothesized that an alteration in the production of endothelium-dependent factors by sex hormones is a potential unifying mechanism for both the decreased arterial contractility and the redistribution of cardiac output characteristic of normal pregnancy. Thus, the effect of pregnancy/ estradiol on any one vascular bed will reflect the number and distribution of estrogen receptors. In this article, we review what is known about the effects of pregnancy and estrogen on nitric oxide synthase. Pregnancy increases Ca(2+)-dependent NOS activity early in gestation. The timing of the increase parallels the increase in plasma estradiol concentration. The increase in maternal brain NOS during pregnancy is blocked by tamoxifen. cGMP content increases along a similar time course in most but not all tissues. The changes in cGMP more closely approximate the changes in blood flow during pregnancy. This suggests that multiple elements of the NO:cGMP pathway are altered by pregnancy. It also shows that cGMP content cannot always be used as a surrogate for NOS activity. Estradiol, but not progesterone or testosterone, increases CA(2+)-dependent NOS activity. NO accounts for some, but not all of the pregnancy-associated changes in maternal arterial contractile response. It is not involved in uterine quiescence. Nitric oxide synthase is developmentally regulated in the fetus and is likely important in regulating the distribution of fetal blood flow.

Brain formation of oestrogen in the mouse: sex dimorphism in aromatase development

Steroid sex hormones have an organizational role in gender-specific brain development. Aromatase, converting testosterone (T) to oestradiol-17 beta (E2), is a key enzyme in the brain and the regulation of this enzyme is likely to determine availability of E2 effective for neural differentiation. In rodents, oestrogens are formed very actively during male perinatal brain development. This paper reviews work on the sexual differentiation of the brain aromatase system in vitro. Embryonic day 15 mouse hypothalamic culture aromatase activity (AA: mean Vmax = 0.9 pmol/h/mg protein) is several times greater than in the adult, whereas apparent Km is similar for both (approximately 30-40 nM). Using microdissected brain areas and cultured cells of the mouse, sex differences in hypothalamic AA during both early embryonic and later perinatal development can be demonstrated, with higher E2 formation in the male than in the female. The sex differences are brain region-specific, since no differences between male and female are detectable in cultured cortical cells. AA quantitation and immunoreactive staining with an aromatase polyclonal antibody both identify neuronal rather than astroglial localizations of the enzyme. Kainic acid eliminates the gender difference in hypothalamic oestrogen formation indicating, furthermore, that this sex dimorphism is neuronal. Gender-specific aromatase regulation is regional in the brain. Oestrogen formation is specifically induced in cultured hypothalamic neurones of either sex by T, since androgen has no effect on cortical cells. Androgen is clearly involved in the growth of hypothalamic neurones containing aromatase. It appears that differentiation of the brain involves maturation of a gender-specific network of oestrogen-forming neurones.

Neuronal aromatase expression in preoptic, strial, and amygdaloid regions during late prenatal and early postnatal development in the rat

Brain aromatase has been considered to be an important clue in elucidating the actions of androgen on brain sexual differentiation. Using highly specific anti-P450arom antiserum, the regional and subcellular distributions were immunohistochemically evaluated in the preoptic, strial, and amygdaloid regions of developing rat brains. Aromatase-immunoreactive (AROM-I) neurons were classified into three groups. The first, in which immunostaining occurs only during certain pre- or neonatal days (E16-P2), included the anterior medial preoptic nucleus, the periventricular preoptic nucleus, neurons associated with the strial part of the preoptic area, and the rostral portion of the medial preoptic nucleus. The second is a striking AROM-I cell group in the "medial preopticoamygdaloid neuronal arc," which extends from the medial preoptic nucleus to the principal nucleus of the bed nucleus of the stria terminalis and the posterodorsal part of the medial amygdaloid nucleus. The AROM-I neurons appeared by E16, reaching a peak in staining intensity between E18 and P2 and diminishing after the perinatal stage. After P14, a third group of AROM-I neurons emerged in the lateral septal nucleus, the oval nucleus of the bed nucleus of the stria terminalis, and the central amygdaloid nucleus. The second group was thought to be the major aromatization center in developing rat brains, while the center might partly shift to the third group of neurons after the late infantile stage. The distribution and developmental patterns were basically similar in males and females, suggesting that the neonatally prominent aromatase is not induced by male-specific androgen surges occurring around birth. On immunoelectron microscopy, subneuronal aromatase was predominantly localized on the nuclear membrane and endoplasmic reticulum, which appeared to be appropriate for the efficient conversion of androgen into estrogen just prior to binding to the nuclear receptors.

Localisation of aromatase activity in androgen target areas of the mouse brain

Oestrogens are formed from androgens in the mouse brain, but the localization of aromatase activity is unresolved. Immunocytochemistry has not detected aromatase in expected key androgen target areas such as the medial preoptic area. Using a micropunch method and a sensitive in vitro 3H2O product detection assay, we report significant aromatase activity in adult male preoptic area (POA) and amygdala with [1 beta-3H]testosterone as substrate (Vmax < or = 1,200 fmol 3H2O formed/mg protein/h), in contrast to cerebrum (Vmax < 18 Units), from two strains of albino mice (BALB/c, Swiss NIHS) and the wild-type, Mus musculus. Aromatase activity was significantly higher in the amygdala than in the POA, particularly in the Swiss NIHS (4.6 x higher). Neonatal preoptic aromatase activity is 4 times higher than in the adult, but the Kms (both approximately 30 nM) suggest that the enzyme does not change during development. Similar inhibition potencies using Fadrozole HCl (IC50 approximately 0.5 nM) also suggest a common form of the enzyme in adult and developing brain. Adult mouse ovarian aromatase activity is higher (Vmax > 3,000 Units), but has a substrate binding constant similar to that of the POA.

Measurement of androgen sensitivity in the human prostate in in vitro three-dimensional histoculture

We have adopted an in vitro three-dimensional histoculture technique for assay of androgen sensitivity in explants of human benign prostatic tissue. The assay is based on the uptake of 3H-thymidine/micrograms protein in explants of prostate incubated in parallel with dihydrotestosterone (DHT) and hydroxyflutamide (HF) controls. The ratio of 3H-thymidine/micrograms protein in DHT treated samples per 3H-thymidine/micrograms protein in HF treated samples provides an index of androgen sensitivity. The DHT/HF index measured in 24 BPH specimens averaged 3.6. To determine the specificity of the HF effect, we measured the DHT/HF index in a single prostate at different concentrations of HF in the presence of fixed concentrations of DHT (2 x 10(-8) M) and noted a dose-response relationship. In addition we noted no effects of HF on 3H-thymidine incorporation over a range of 2 x 10(-4)M compared to 2 x 10(-7)M, except at the highest concentration. Of surprise was the finding of an average DHT/HF index in 5 different nonprostate tissues, including breast, uterus, colon, kidney, and thyroid, that was similar to the index found in prostates. We plan to adapt this androgen sensitivity assay to measure the DHT/HF index in biopsy-size samples of prostate, since such an assay could then be utilized to determine androgen sensitivity in individual patients with prostate cancer.

Estrogen and the etiology of anorexia nervosa

Most patients suffering from anorexia nervosa are women, but the types and relative contributions of social, psychological, or organic characteristics of women that make women more likely to develop this feeding disorder are uncertain. In this theoretical review, evidence that the female sex hormone, estrogen, contributes to the symptoms seen in anorexia and underlies the sex difference in incidence is discussed. Current data on the anorexic potency of estrogen in experimental animals, humans, and in anorexic patients is presented, along with a suggestion that treatment of anorexics with progesterone, a hormone that blocks these effects of estrogen, might have a beneficial influence upon the outcome of anorexia nervosa.

Steroid hormones and the cardiovascular system: direct actions of estradiol, progesterone, testosterone, gluco- and mineralcorticoids, and soltriol [vitamin D] on central nervous regulatory and peripheral tissues

Knowledge of steroid hormone sites of action and related effects in cardiovascular and neural regulatory tissues is reviewed. Evidence for nuclear receptor sites is derived mainly from autoradiographic studies with relatively intact tissues and some biochemical studies with tissue homogenates. In the heart and in the walls of blood vessels, estradiol, dihydrotestosterone, corticosterone, aldosterone, dexamethasone, and soltriol (vitamin D) show nuclear binding. In the brain and spinal cord, neuronal regions associated with cardiovascular regulation contain nuclear receptors in specific patterns for each steroid hormones, including progesterone and soltriol. These data indicate that all steroid hormones exert direct actions on the cardiovascular system at its different levels of organization, thus enabling adjustment to the changing demands during reproduction (gonadal steroids), stress (adrenal steroids), and solar seasons (vitamin D-soltriol).