Large benign virilizing adrenal adenoma

The young woman described sought evaluation for infertility and was found to have virilization due to a large left adrenal tumor. Further endocrine studies confirmed a syndrome of pure virilization with normal glucocorticoid function. Resection of this apparently benign tumor resulted in regression of virilization, as well as pregnancy. Pure virilization is an unusual manifestation of benign adrenocortical tumors, and adrenal tumors of this size are most frequently malignant.

Factors affecting the conversion of androstenedione to estrogens by human fetal hepatocytes in monolayer culture

The purpose of the present investigation was to characterize and determine what hormones affect the activity of aromatase in human fetal hepatocytes maintained in primary monolayer culture. The major product of aromatization of androstenedione was estrone sulfate. Optimal conditions for assay of aromatase activity in fetal liver cells were determined. The apparent Km for androstenedione was 50 nM. Aromatase activity was stimulated by glucocorticoids in the presence of fetal calf serum. The concentration of dexamethasone required for half-maximal stimulation was 10(-8) M, similar to the concentration required for half-maximal binding to glucocorticoid receptors. This action of dexamethasone was inhibited by cortisol 21-mesylate, a glucocorticoid antagonist. Aromatase activity was also stimulated by (Bu)2cAMP and cholera toxin, and was inhibited by fetal calf serum. This effect of fetal calf serum was mimicked by epidermal growth factor. However, epidermal growth factor did not mimic the permissive action of serum to stimulate aromatase activity by dexamethasone. In these respects, the regulation of aromatase activity of human fetal hepatocytes is similar to that of human adipose stromal cells. A polycyclic hydrocarbon, benzo(a)pyrene, which causes induction of aryl hydrocarbon hydroxylase activity in fetal hepatocytes, inhibited the stimulation of aromatase activity by dexamethasone. Of a number of hormones tested, including glucagon, insulin, angiotensin II, ACTH, hCG, GH, PRL, and T3, only glucocorticoids were effective in stimulating aromatase activity of human fetal hepatocytes. These results emphasize the complex and multiparameter nature of the regulation of aromatase activity in this as in other tissues.

Effects of aging and obesity on aromatase activity of human adipose cells

Adipose tissue is the principal site of estrogen formation in postmenopausal women; with advancing age as well as with increased body weight, there is an increase in the fractional conversion of circulating androstenedione to estrone. We have studied the effects of aging as well as body weight on aromatase activity of adipose tissue specimens taken from 50 women of various ages and weights. Since aromatase activity of adipose tissue is detectable primarily in stromal cells, these cells were incubated with [1-3H]androstenedione (150 nM), and estrogen formation was assayed by measuring the incorporation of tritium into [3H]water. The aromatization rate, when normalized on the basis of equal numbers of cells, increased with increasing age (P less than 0.03; r = 0.43). In contrast, when expressed as a function of body weight, no change in aromatase activity of adipose stromal cells were found. Aromatization of androstenedione by cells from young women who had undergone oophorectomy was not increased compared with that of cells from young women with normal ovarian function, indicating that the onset of menopause per se and the accompanying increase in circulating gonadotropin levels were not causative factors in the increased aromatase activity of adipose stromal cells. We conclude, therefore, that increased estrone production associated with aging may result from an increase in the specific activity of the aromatase enzyme in adipose stromal cells and is not affected by changes in gonadotropin concentrations associated with menopause. On the other hand, the increase in estrogen formation as a function of obesity is probably due to increased numbers of adipose cells, rather than to an increase in the specific activity of aromatase in those cells.

Regulation of aromatase activity of cultured adipose stromal cells by catecholamines and adrenocorticotropin

Adipose tissue is the major site of estrogen formation in postmenopausal women. We have previously reported (Simpson, E.R., Ackerman, G.E., Smith, M.E. and Mendelson, C.R. (1981) Proc. Natl. Acad. Sci. (U.S.A.) 78, 5690-5694; Mendelson, C.R., Cleland, W.H., Smith, M.E. and Simpson, E.R. (1982) Endocrinology 111, 1077-1085) that aromatase activity of human adipose stromal cells in culture is stimulated by glucocorticoids and by dibutyryl cyclic AMP (Bt2-cAMP). In order to establish which physiological factors might stimulate aromatase activity of these cells by activation of adenylate cyclase, we have investigated the roles of adrenocorticotropin (ACTH) and isoproterenol to increase cyclic AMP levels and stimulate the aromatization of androstenedione. In the presence of methylisobutylxanthine (MIX), ACTH stimulated cyclic AMP formation and aromatase activity in a time- and concentration-dependent manner. The concentration of ACTH required for half-maximal stimulation was approximately 10(-8) M. Isoproterenol, in the presence of MIX, stimulated cyclic AMP formation in a time- and concentration-dependent fashion, and also stimulated aromatase activity. These effects of isoproterenol appeared to be mediated by binding of the agonist to a population of beta-adrenergic receptors. On the basis of these and our previous studies, we suggest that ACTH may play an important role in stimulating estrogen formation by human adipose tissue, both directly, and by stimulating the adrenal cortex to produce both substrate, androstenedione, and inducing agent, namely cortisol.

Aromatase activity of membrane fractions of human adipose tissue stromal cells and adipocytes

Adipose tissue is the principal site of extraglandular estrogen formation in nonpregnant women. The importance of adipose tissue as a site of estrogen formation is emphasized by the finding that increased body weight is associated with an increased incidence of endometrial carcinoma. In the present study, the kinetics of estrogen formation from androstenedione by adipocytes and by stromal cells isolated from human adipose tissue as well as by membrane fractions prepared from these cells were investigated. Subcutaneous adipose tissue samples obtained from women were dispersed by collagenase treatment, and aromatase activity was assayed by the incorporation of tritium from [1-3H]androstenedione into [3H]water. As previously reported, aromatase activity was found in intact stromal cells of adipose tissue, whereas little aromatase activity was detected in intact adipocytes. When crude membrane fractions (100,000 X g pellet) of stromal cells and adipocytes were incubated in the presence of [1-3H]androstenedione and an NADPH-generating system, however, aromatase activity was found in membrane fractions of both stromal cells and adipocytes, and estrogen formation increased in a linear manner as a function of time and membrane protein concentration. The apparent Michaelis constant (Km) of aromatase for androstenedione of intact stromal cells was 0.03 microM, whereas intact adipocytes did not convert androstenedione to estrone at substrate concentrations up to 3.0 microM. In membrane fractions of stromal cells, the rate of aromatization as a function of androstenedione concentration did not follow simple Michaelis-Menten kinetics, and both low affinity (Km = 1.03 microM) and high affinity (Km = 0.10 microM) components were observed. The affinity of androstenedione for aromatase of adipocyte membrane fractions was low; the rate of aromatization was not saturable at concentrations of androstenedione up to 3.0 microM. When intact adipocytes were incubated with [1-3H]androstenedione, then homogenized, and the homogenate was treated by differential centrifugation, the radioactivity that was added to the medium was found almost entirely in the lipid fraction of the cells. This finding is indicative that the low aromatase activity in intact adipocytes is the result of sequestration of steroid in lipid droplets in the cells. We suggest that the stromal cells of adipose tissue are a major source of the increased estrogen production in obese persons; a role for adipocytes in the regulation of adipose tissue estrogen formation, however, cannot be excluded at this time.

Inhibition of prostaglandin biosynthesis in human adipose tissue by glucocorticosteroids

Cultured stromal cells derived from human sc adipose tissue synthesized and secreted into the medium prostaglandin E2 (PGE2), PGF2 alpha, and 6-keto-PGF1 alpha, a metabolite of prostacyclin. PGE2 was quantitatively the major PG formed by these cells. Dexamethasone inhibited PG biosynthesis in a concentration- and time-dependent manner; dexamethasone (2.5 X 10(-10) M) caused greater than 50% inhibition of PGE2 synthesis after 24 h of incubation and 90% inhibition after 48 h. The effect of dexamethasone to inhibit PGE2 synthesis was blocked by simultaneous incubation of cells with cortisol-21-mesylate, an antagonist of the binding of glucocorticosteroids to cytosolic receptors. (Bu)2cAMP (1 mM), forskolin (10 microM), and 1-methyl-3-isobutylxanthine (0.1 mM) markedly stimulated PGE2 biosynthesis in cultured adipose stromal cells. The inhibitory effect of dexamethasone on PGE2 synthesis was attenuated by simultaneous incubation of cells with (Bu)2cAMP. The results of this study suggest that glucocorticosteroids inhibit PG biosynthesis in adipose tissue stromal cells, whereas cAMP and certain analogs thereof stimulate PG biosynthesis and overcome the inhibitory action of glucocorticosteroids.

Aromatization of androgens by human adipose tissue in vitro

Stromal cells prepared from adipose tissue of women were maintained in monolayer culture to study the regulation of aromatase activity by hormones. Aromatase activity was stimulated 20-100-fold by dexamethasone. Half-maximal stimulation of aromatase activity was attained at a dexamethasone concentration of 2.5 nM. The stimulatory effect of dexamethasone was apparent after a preincubation time of 4 h, and stimulation was maximal after 24 h of preincubation. The stimulatory effect of dexamethasone was observed only when fetal calf serum also was present in the culture medium. Of the various steroids tested, dexamethasone was the most potent in stimulating aromatase activity. Cytosolic fractions prepared from stromal cells that had been maintained in monolayer culture were found to contain a homogeneous population of sites that specifically bound [3H]-dexamethasone with relatively high affinity (Kd = 2.9 nM) and low capacity (38 fmol/mg of protein). The stimulatory effect of dexamethasone on aromatase activity was prevented by simultaneous incubation with cortisol 21-mesylate (0.1-10 microM), a compound known to block the binding of glucocorticosteroids to cytoplasmic receptors. These findings are suggestive that glucocorticosteroids act to increase aromatase activity in stromal cells by binding to a glucocorticosteroid receptor. This presumably results in the induction of synthesis of specific proteins, perhaps the form of cytochrome P-450 involved in aromatization, or else NADPH-cytochrome P-450 reductase. Aromatase activity was also stimulated by dibutyryl cyclic AMP ( (Bu)2cAMP). In contrast to the stimulation by dexamethasone, the effect of (Bu)2cAMP was diminished by 70% when fetal calf serum (15%) was present in the culture medium. Aromatase activity of cells incubated with (Bu)2cAMP continued to increase over an 8 day period, at which time, enzyme activity was increased by 200-fold. Aromatase activity of stromal cells maintained in the presence or absence of serum was unaffected after incubation for 5 days with oFSH, hCG, bPRL, hGH or soterenol. On the other hand, incubation of cells for 5 days with cholera toxin (10 micrograms/ml) or 1-methyl-3-isobutylxanthine (0.1 mM) resulted in a marked increase in aromatase activity; the effect of these agents was diminished greatly when serum was present in the culture medium. The findings that serum inhibited the stimulation of aromatase activity by (Bu)2cAMP and that the time courses of aromatase induction by (Bu)2cAMP and dexamethasone were markedly different are suggestive that different molecular events mediate aromatase induction by glucocorticosteroids and cyclic AMP.