Brain Aromatase Activity Research Articles

Aromatase activity in marsupial brain, ovaries, and adrenals

In contrast to numerous other vertebrate groups in which there is biochemical evidence for aromatase activity in brain tissues, estrogen synthesis was not detectable in the CNS of a North American marsupial, the Virginia opossum. In the present study, the occurrence of aromatase activity in marsupial brain and other tissues was reinvestigated using the Australian species, Macropus eugenii and Trichosurus vulpecula. Following incubation of tissue homogenates with [7- 3H]androstenedione and an NADH-NADPH generating system, estrogen products were isolated and finally identified by methylation and crystallization to constant specific activity. No estrogen was detectable in samples of adult brain; however, the brain of wallaby pouch young conformed to the general vertebrate pattern. Not only were small amounts of authentic estrone synthesized, but aromatization was greatest in limbic areas and activity per unit protein in all regions progressively declined with age. The ovaries of Macropus and Trichosurus as well as the adrenals of Macropus were also capable of converting labeled substrate to estrone or estradiol-17β. This study provides the first definitive evidence for synthesis of conventional eutherian estrogens in Metatheria.

Maternal stress decreases steroid aromatase activity in brains of male and female rat fetuses.

Steroid aromatase activity was measured in homogenates of combined hypothalamic and amygdaloid specimens obtained from 17- to 21-day-old male and female rat fetuses. The fetuses were obtained both from normal mothers and mothers exposed to a regimen of stress that results in a failure of behavioral masculinization and defeminization of male offspring. Tissue samples from stressed mothers and controls were obtained during the dark phase of the day (Villanova group, days 17, 18, 19, 20 and 21 postconception). Additional samples were obtained during the light phase (Hershey group, days 17.5, 18.5, 19.5 and 20.5 postconception). The aromatase assay used, based on the measurement of tritiated water formed during an incubation with [lβ-³H] androstenedione, had a sensitivity of 10–15 fmol per tube. There was no sex difference in aromatase activity in fetuses of either control or stressed mothers. When data from the two sexes were combined, the following sfatistically significant effects were identified: (1) lower aromatase activity in stressed compared with control fetuses on days 18, 19 and 20 postconception, (2) a progressive decline in enzyme activity between days 18.5 and 20.5 postconception in the Hershey group (controls) and between days 19 and 20 in both the control and stressed fetuses in the Villanova group, and (3) an increase in enzyme activity in the stressed fetuses between days 20 and 21. No relationship was evident between steroid aromatase activity in brain and circulating testosterone levels in male fetuses as determined in a previous study. Failure to detect sex differences or an effect of testosterone on aromatase activity could be due to tissue dilution since enzyme activity may be concentrated in a few discrete nuclear regions. Measurement of enzyme activity in these regions is needed before arriving at any definitive conclusions.

Estrogen synthesis in vitro and in vivo in the brain of a marine teleost (Myoxocephalus).

Conversion of radiolabeled substrate to estrone and estradiol was studied in a marine teleost, Myoxocephalus octodecimspinosus (longhorn sculpin), a species previously shown to have exceptionally high brain aromatase activity. In vitro aromatization of 3H-labeled androstenedione was greatest in homogenates of the preoptic area/anterior hypothalamus, medial telencephalon, and lateral telencephalon, in that order, and when measured in individual fish, marked sex and seasonal differences were observed. Relatively little estrogen was produced by the inferior lobes of the hypothalamus, thalamus, optic lobes, basal midbrain, cerebellum, and medulla. Sculpin testis was aromatase negative, and at no time did ovarian activity per unit weight exceed that in the brain. Addition of 11β-hydroxy- and 11-ketotestosterone to forebrain homogenates did not alter estrogen yields. Following perfusion of a sculpin head preparation with 3H-labeled 19-hydroxyandrostenedione, estrone was isolated from the efferent perfusate and estrone and estradiol recovered from the brain and pituitary. The authenticity of formed estrogen in this experiment was verified by derivative formation and recrystallization. Estrogen concentration was highest in the preoptic area/hypothalamus, somewhat lower in the medial and lateral telencephalon, and lowest in the remaining brain regions. Pituitary estrogen per unit weight was at least 12 times higher than in any brain region and, in contrast to the brain in which estrone predominated, the greatest proportion of total estrogen was estradiol. No authentic estrogen was recovered from non-neural tissues (liver, kidney, heart, muscle, skin, and gills) after perfusion. All of the above findings show that the highest levels of aromatase activity correspond neuroanatomically to the reported distribution of estrogen-binding cells and the location of reproductive control centers in the teleost brain. In these regions, a correlation between CNS estrogen production and reproductive status (gender and season) is further evidence for a functional interrelationship. The presence of relatively large amounts of estrogen in the sculpin pituitary following perfusion with radiolabeled androgen suggests that, at this level of phylogeny, the brain may regulate pituitary function by supplying estrogen directly, or the pituitary itself is capable of aromatization. Whether or not brain-derived estrogen makes a significant contribution to the peripheral estrogen pool is still open to question.

Identification of aromatase in the reptilian brain.

The present study tests the hypothesis that brain aromatase is an "ancient" property of nervous tissue and may be identified in homologues of the limbic system in a non-mammalian vertebrate, the turtle Chrysemys picta. Tissue homogenates (180 mg wet weight/2 ml) were incubated with [7 alpha-3H]androstenedione and cofactors for 60 min at 37 C. Estrone (E1) was isolated and characterized by thin layer chromatography, methylation and recrystallization to constant specific activity. No estradiol-17 beta was detected. Aromatase was found only in the forebrain but was diffusely distributed throughout this major brain division. No other neural or non-neural tissues, including mid- and hindbrain structures, testis, and ovary, synthesized detectable quantities of E1 in our system. The strio-amygdaloid complex of both sexes synthesized more E1 per unit weight than the preoptic-hypothalamic area (POA-HTH) or other forebrain structures. It is possible that the conversion of androgen to estrogen has biological significance in this species since the reaction occurred throughout the physiological temperature range experienced during activity in nature and sex differences in brain aromatase activity during the breeding season were apparent. These experiments in Chrysemys demonstrate that the synthesis of estrogen from androgen by the brain is not limited to mammals, but also occurs at a more primitive level of phylogenetic development. Restriction of aromatase to forebrain structures of the turtle is consistent with the neuroanatomic distribution of enzyme activity in the limbic system of mammals. Estrogen yield from adult turtle brain incubates (3.2-22.6 pmol/g) is more like that reported for fetal (2.7-33 pmol/g) than for adult (0.1-1.9 pmol/g) mammals. We suggest that the in situ synthesis of estrogen by the central nervous system has its orgins early in vertebrate evolution and may be a primitive characteristic of brain-steroid interactions that regulate physiological and behavioral sex in vertebrates.