Distribution Of Aromatase Activity Research Articles

Distribution of aromatase activity in brain and peripheral tissues of male sheep: effect of nutrition

Conversion of testosterone to oestradiol plays a major role in the feedback inhibition of gonadotrophin secretion in male sheep but little is known of the distribution or control of aromatase activity among central and peripheral tissues. Changes in activity at those sites may mediate alterations in the effectiveness of negative feedback following, for example, a change in nutrition. Using a tritiated-water assay, we quantified aromatase in several tissues in mature male sheep, assessed their contribution to oestradiol production, and tested whether activity at each site was affected by a nutritional treatment that stimulates gonadotrophin secretion. Among the brain tissues, the preoptic area had the highest concentration of activity, followed by the hypothalamus, amygdala and cortex. Among the peripheral tissues, liver and testis had the highest activity and, due to their mass, they are the major sources of circulating oestradiol. Pituitary, muscle, kidney and adipose tissues had very low aromatase levels. The nutritional stimulus increased activity in testis but not in liver or brain. We conclude that changes in aromatase activity do not mediate the effects of nutrition on steroid feedback, but aromatisation in testis, liver and brain is important in the endocrine regulation of reproduction in the mature ram.

Distribution of Aromatase Activity in the Brain and Peripheral Tissues of Passerine and Nonpasserine Avian Species

Many behavioral effects of testosterone on hypothalamic and limbic brain areas are mediated by the action, at the cellular level, of estrogens derived from local testosterone aromatization. Aromatase activity and cells containing the aromatase protein and mRNA have accordingly been identified in the brain areas involved in the control of behavior. The presence of an unusually high level of aromatase activity has been detected in the telencephalon of one songbird species, the zebra finch (Taeniopygia guttata), and it is suspected that this high telencephalic aromatase may be a specific feature of songbirds but this idea is supported only by few experimental data. The distribution of aromatase activity in the brain of zebra finches and of one nonsongbird species, the Japanese quail (Coturnix japonica), was compared with the distribution of aromatase activity in the brain of four species of free-living European songbirds, the chaffinch (Fringilla coelebs, Fringillidae), willow warbler (Phylloscopus trochilus, Sylviidae), great tit (Parus major, Paridae), and pied flycatcher (Ficedula hypoleuca, Muscicapidae). High levels of enzyme activity were observed in the diencephalon of all species. The high levels of aromatase activity that had been observed in the zebra finch telencephalon and were thought to be typical of songbirds were also present in the four wild oscine species but not in quail. None of these songbird species had, however, a telencephalic aromatase activity as high as that in the zebra finch, which may represent an extreme as far as the activity of this enzyme in the telencephalon is concerned. Measurable levels of aromatase activity were also detected in all songbird species in the liver and in the three other brain areas that were assayed, the optic lobes, cerebellum, and brain stem, with the exception of the cerebellum in willow warblers and quail, but no detectable activity was observed in the testes, muscle, and adrenals of all species. Additional studies will be needed to identify the functional significance of estrogen synthesis in areas that are not classically known to be implicated in the control of reproduction. Within a given species, the birds that had the highest plasma testosterone levels also displayed the highest levels of diencephalic aromatase activity and the interspecies differences in the two variables were positively related. This raises the possibility that the absolute level of diencephalic aromatase represents a species-specific characteristic under the control of plasma testosterone levels. There was, in contrast, no correlation between the aromatase activity in the telencephalon and the plasma testosterone levels but the enzyme activity was correlated with the plasma levels of luteinizing hormone. These data bring additional support to the idea that the diencephalic and telencephalic aromatases are controlled by independent mechanisms.

Distribution of aromatase activity in cultured neurons and glia cells

Aromatase plays a crucial role in the mechanism of action of testosterone in the central nervous system. Nevertheless, the exact cellular localization of this enzymatic complex within the different cell populations of the brain is still uncertain. In the experiments described here the presence of aromatase (assayed by the tritiated water method) has been evaluated in the two main cellular components of the brain: neurons and glia. Neurons, mixed glial cells, type 1 astrocytes, were obtained in cultures; oligodendrocytes were prepared by gradient ultracentrigugation. The results indicate that, among the different cells tested, only neurons possess a significant degree of aromatase activity, while the enzymatic activity is extremely low in mixed glial cell and in astrocyte preparations. Oligodendrocytes seem to be completely inactive in this respect.

Distribution of aromatase in the brain of the Japanese quail, ring dove, and zebra finch: An immunocytochemical study

An immunocytochemical peroxidase-antiperoxidase procedure using a purified polyclonal antibody raised against human placental aromatase was used to localize aromatase-containing cells in the brain of three avian species: the Japanese quail, the ring dove, and the zebra finch. In quail and dove, immunoreactive cells were found only in the preoptic area and hypothalamus, with a high density of positive cells being present in the medial preoptic area, in the septal area above the anterior commissure, in the ventromedial nucleus of the hypothalamus, and in rostral part of the infundibulum. Immunoreactivity was weaker in zebra finches, and no signal could therefore be detected in the ventromedial and tuberal hypothalamus. The positive material was localized in the perikarya and in adjacent cytoplasmic processes, including the full length of axons always leaving a clear unstained cell nucleus. These features could be observed in more detail on sections cut from perfused brains and stained with an alkaline phosphatase procedure. The distribution of aromatase immunoreactivity was similar in the three species although minor differences were observed in the preoptic area. The localization of labelled neurons coincided with the distribution of aromatase activity as studied by in vitro radioenzyme assays on brain nuclei dissected by the Palkovits punch method. There was one striking exception to this rule: no immunoreactivity was detected in the zebra finch telencephalon, while assays had shown the presence of an active enzyme in several nuclei such as the robustus archistriatalis, the hyperstriatum ventrale pars caudale, and the hippocampus and area parahippocampalis. The origins of this discrepancy and the functional role of the aromatase observed in the axons are discussed.

The apparent shift in distribution of aromatase activity in the subcellular fraction of human term placenta stored at -96 degrees C.

The effects of storage at -96 degrees C on the distribution of the total aromatase activity in the homogenate, 900 xg pellet and 900 xg supernatant of two human term placentas were studied. Both specific and total aromatase activities in the 900 xg pellet increased through storage at -96 degrees C, while that in the 900 xg supernatant decreased. The ratio of total aromatase activity between the 900 xg pellet and 900 xg supernatant was about 2:1 in fresh placenta, but the ratio was about 19:1 in placenta stored at -96 degrees C for 3.5 months. Total aromatase activity in the tissue homogenate remained fairly constant throughout five months of storage at -96 degrees C. These data indicate that although active microsomal aromatase is thought to be available only from fresh placenta and the activity is lost quickly during storage of the tissue, aromatase itself is stable for months at -96 degrees C and the 900 xg pellet prepared from the frozen tissue contains almost the total original aromatase activity in the fresh placental tissue.

Distribution of aromatase activity in quail brain (C.c. [formula omitted]): Effects of photoperiod and castration

Distribution of aromatase activity in quail brain (C.c. [formula omitted]): Effects of photoperiod and castration