Tissue and species specificity of unmasked nuclear acceptor sites for the estrogen receptor of Squalus testes

Negative feedback control of the spermatogenic progression by testicular oestrogen synthesis: insights from the shark testis model

The organisation of the testis of the dogfish shark is technically advantageous for stage-by-stage analysis of spermatogenesis in vivo and in vitro. Prior studies using this model show that total oestrogen receptors (ER) are concentrated in regions where spermatocysts ("follicle-like" germ cell-Sertoli cell units) are in stem cell and spermatogonial stages: respectively, germinal zone (GZ) and premeiotic (PrM) regions. By contrast, key enzymes regulating oestrogen (E) concentrations (aromatase, 17 alpha-hydroxylase) are maximal in meiotic (M) and postmeiotic (PoM) regions, respectively, which are upstream in the intratesticular vascular pathway. To investigate the hypothesis that E is part of a signalling mechanism between stages of development, studies were undertaken to test direct effects of oestradiol-17 beta (E2) on processes in ER-rich regions. As measured by [3H]thymidine (-Tdr) incorporation. DNA synthesis in GZ and PrM regions was inhibited by E2 (0-1000 nM) in a dose-response fashion. The maximal response (30-40%) was significant, reproducible and observed within 72 hr of treatment. Insulin differentially affected DNA synthesis and the response to E2 in GZ in GZ and PrM regions. As measured by [3H]Tdr release after prelabelling spermatocysts of GZ regions, apoptosis progressively decreased with increasing concentrations of E2. At the maximal dose of E2 used, there was no effect on total protein synthesis or secretion in combined GZ/PrM cysts, indicating that effects on DNA synthesis and cell death were authentically physiological, not pharmacological, and consistent with a state of developmental arrest. These results support the hypothesis that E synthesised within the testis is part of a negative feedback regulatory mechanism whereby more mature stages regulate the developmental advance of less mature stages. A growth control mechanism of this type could explain the strict temporal, spatial and quantitative order of succeeding stages characteristic of normal spermatogenesis in all vertebrates. Further study is required to determine whether E signalling in this model is restricted to Sertoli cells or has a germ cell component.

Nuclear matrix acceptor binding sites for steroid hormone receptors: a candidate nuclear matrix acceptor protein

Steroid/nuclear-hormone receptors are ligand-activated transcription factors that have been localized to the nuclear matrix. The classic model of hormone action suggests that, following activation, these receptors bind to specific "steroid response elements" on the DNA, then interact with other factors in the transcription initiation complex. However, evidence demonstrates the existence of specific chromatin proteins that act as accessory factors by facilitating the binding of the steroid receptors to the DNA. One such protein, the "receptor binding factor (RBF)-1", has been purified and shown to confer specific, high-affinity binding of the progesterone receptor to the DNA. Interestingly, the RBF-1 is localized to the nuclear matrix. Further, the RBF-1 binds specifically to a sequence of the c-myc proto-oncogene that has the appearance of a nuclear matrix attached region (MAR). These results, and other findings reviewed here, suggest that the nuclear matrix is involved intimately in steroid hormone-regulated gene expression.

Cell-cell interactions in the testis of teleosts and elasmobranchs

In this paper we present the state of knowledge on cell-cell interactions in the testis of two groups of anamniote vertebrates--teleosts and elasmobranchs--which include most fish. In these fish, the structural organization of the testis differs fundamentally from that which characterizes amniotes in which the germinal tissue is located in tubules open at both ends and consists of a permanent population of Sertoli cells associated with successive stages of germ cell development. In fish, the spermatogenic unit of testis is the spermatocyst, which corresponds to one germ cell or to a clone of isogenetic germ cells, enclosed by one or several Sertoli cells, which form the wall of the cyst. In fish testis, the Sertoli cells do not represent a permanent population of cells. Although both are of the cystic type, the teleost and elasmobranch testes are differently organized. In elasmobranchs, primary spermatogonia and Sertoli cells lie initially free within the interstitial tissue, before becoming sequestered by a basement membrane; the testis is then composed of a mass of spermatocysts which contain many Sertoli cells, each being associated with a clone of germ cells. In contrast, in teleosts, the cysts are confined to large elongated structures limited by a basement membrane. These structures are either lobules originating under the albuginea or tubules which, in contrast to those of mammals, are anastomosed. In the lobules, the spermatocysts start to develop at the blind end of the lobules and migrate towards the efferent system, whereas in the tubules, the spermatocysts are located against the basement membrane, all along the tubules and do not migrate. In elasmobranchs, unlike teleosts, Leydig cells are either absent from the interstitial tissue or rare and undifferentiated and their role in steroid production is at best marginal. While many studies have focused on topographical and functional interactions between the diverse cell types present in mammalian testis, only a few studies have brought particular attention to these aspects in fish. In fish, like in mammals, testicular cell-cell interactions are based on structural elements and chemical factors. Occasionally, various adhering junctions have been observed, essentially in teleosts, between Sertoli cells, between Sertoli cells and germ cells, between germ cells themselves, and interstitial cells. Furthermore, in some teleost species, using horseradish peroxidase or lanthanum salts, the presence of tight junctions between Sertoli cells has been correlated to the occurrence of a Sertoli barrier. In these species, the barrier develops after meiosis so that only haploid germ cells are shielded from the vascular system. In fish, recent development of techniques which enable the preparation and in vitro culture of enriched populations of testicular cells and of spermatocysts, has allowed investigations on functional aspects of cell-cell interactions. In particular, data have been obtained, in the trout, on the control of spermatogonia proliferation by Sertoli cell-conditioned media and, in the dogfish, on the steroidogenic activity of Sertoli cells, in relation to the differentiation stage of the associated germ cells. Furthermore information exists, in the trout, showing that intratubular macrophages may participate in the re-initiation of spermatogonial proliferation. In conclusion, the cytoarchitecture of fish testis, as compared to that of mammals, presents original features which provide unique opportunities to develop fruitful studies for a better understanding of the complex control mechanisms underlying testicular function in vertebrates.

Estrogen receptors in the human male bladder, prostatic urethra, and prostate. An immunohistochemical and biochemical study

The distribution and quantity of estrogen receptors (ERs) in the human male bladder, prostatic urethra and the prostate were studied in eight males with recurrent papillomas of the bladder or monosymptomatic hematuria (median age 61 years), 14 men undergoing transurethral resection due to benign prostatic hyperplasia (median age 70 years), and nine men undergoing cystectomy due to malignant tumour of the bladder (median age 70 years). In the first group of patients, biopsies for immunohistochemical examination were obtained from the bladder vault, bottom, both side-walls, the trigone area, and the mid-portion of the prostatic urethra, and in the second group from three locations of the prostatic urethra (bladder neck, mid-portion and veramontanum). In the third group, tissue specimens were taken from the vault of the bladder, prostatic urethra, and the prostate, for immunohistochemical as well as biochemical analysis. In the first group, ERs were found in three out of eight specimens of the prostatic urethra, and in one of these, ERs were confined to periurethral glands. ERs could not be demonstrated in any of the bladder-biopsies. In the second group, ERs were not found in the bladder neck, but were seen in four preparations from the veramontanum and in two from the midportion of the urethra. ERs were located in the urothelium and periurethral glands. In the third group, ERs were seen immunohistochemically in the prostatic urethra (two cases) and the prostatic stromal tissue (two cases). ERs could be demonstrated in the bladder neither by immunohistochemistry nor biochemically.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical localization of the avian progesterone receptor and its candidate receptor binding factor (RBF-1)

An avian oviduct nuclear matrix protein in the 6-10 kDa size range has been implicated to function in the cell-free nuclear binding of the avian oviduct progesterone receptor (PR). This protein, termed the receptor binding factor-1 (RBF-1), has been purified and partially characterized [Schuchard et al.: Biochemistry 30:4535-4542, 1991]. This paper describes the immunohistochemical co-localization of the RBF-1 and PR in the avian oviduct cell nuclei and rat reproductive cell nuclei using antibodies directed specifically against the RBF-1 and activated PR. In the undifferentiated oviduct, the immunoreactivities for both PR and RBF-1 were co-localized in the nuclei of only epithelial cells, but not the stromal cells or smooth muscle cells. In the partially differentiated oviduct of estrogen treated chicks, the immunoreactivity co-localized in the nuclei of not only epithelial but also glandular and stromal cells. Staining for the PR, but not RBF-1, was detected in the smooth muscle cells. The intensity of the PR but not the RBF-1 staining was markedly down-regulated in these cells at 2 and 6 h after treatment of the animals with progesterone (P). However, the band patterns for RBF-1 in the Western blots did show qualitative changes which may reflect P-induced posttranslational modifications which alter the epitope on the RBF-1. Interestingly, immunohistochemical analysis of several reproductive tissues of the rat showed that certain cell types in the uterus, ovary, and prostate displayed strong positive nuclear staining for an RBF-1-like antigen(s).(ABSTRACT TRUNCATED AT 250 WORDS)

Cell-cell interactions in the testis of the dogfish: stage-related changes in protein synthesis

Previous studies have shown that the testis of Selachians is a very suited model to study stage-dependent changes in Sertoli cells during spermatogenesis (Dubois and Callard 1989; Sourdaine et al. 1990). In the dogfish testis (here: Scyliorhinus canicula), germ cells, at an identical stage of spermatogenesis, are associated with Sertoli cells to form spermatocysts, which are arranged in zones corresponding to the different stages of spermatogenesis. Using previously described methods for the isolation and culture of spermatocysts from four spermatogenic stages (spermatogonia, spermatocytes, early spermatids and late spermatids; Sourdaine and Jégou 1989; Sourdaine and Garnier 1992) and electrophoresis techniques (1D and 2D-SDS-PAGE) we have investigated the [(35)S] methionine incorporation into proteins in the dogfish testis. Our results indicate that protein synthesis reaches a maximum in spermatocysts with spermatocytes. Marked stage-related changes of protein synthesis and secretion were also observed on the autoradiograms of 1D and 2D-SDS-PAGE. Further investigations of the paracrine control of germ cells on Sertoli cell protein synthesis requires the identification of specific Sertoli cell proteins in the dogfish.

Sulfoconjugation of steroids and the vascular pathway of communication in dogfish testis

The zonal testis of the dogfish (Squalus acanthias) has proven advantageous to study biochemical changes in relation to stage of spermatogenesis, including information on steroidogenic enzymes and steroid receptors. To investigate whether sulfotransferase is part of a mechanism regulating the availability of biologically active hormone in close proximity to receptors, we measured in vitro conversion of [3H]estrone (E1) to sulfoconjugated metabolites in cytosolic subfractions of testes grossly dissected according to germ cell composition (premeiotic-PrM, meiotic-M, and postmeiotic-PoM stages). Assays were carried out in the presence of adenosine 3'-phosphate 5'-phosphosulfate (PAPS) at 22 degrees C and optimized for time (60 min) and protein (500 micrograms/ml). Michaelis-Menten kinetics and saturation analysis gave the following reaction constants for [3H]E1: Km = 0.33 microM, Vmax = 2.5 pmol/min/mg; and for PAPS: Km = 33 microM, Vmax = 1.1 pmol/min/mg; competition studies carried out in the absence or presence of 1- or 5-fold excess radioinert steroids indicated that estrogen (E2 > E1) as well as androgens (T = DHEA > 5 alpha dihydrotestosterone, DHT) were effective inhibitors. Sulfotransferase activity was found to be stage-related, being highest in PoM regions (2.31 +/- 0.24 pmol/min/mg protein) when compared to M and PrM regions (1.22 +/- 0.22 and 1.28 +/- 0.21 pmol/min/mg protein, respectively). Sulfoconjugation and the intratesticular distribution of steroid sulfates were also measured in vivo by perfusion of the intact testis with [3H]androgen or -estrogen. The pathway of blood flow via the genital artery was epigonal organ-->PoM-->M-->PrM (mature-->immature). Perfused [3H]E2, T, and DHT were all extensively metabolized in a one-pass, 1 hr perfusion, less than 10% of perfused [3H] steroid being recovered from testicular tissues as unchanged steroid. In general, recovery of polar metabolites was greater than non-polar metabolites from all three substrates. Sequential hydrolysis with glucuronidase and glusulase indicated that sulfoconjugation is a minor component (< 20%) of several "inactivating" pathways, which include glucuronide conjugation, 17-ketosteroid synthesis, and pathways leading to unidentified polar metabolites. No consistent stage-related distribution patterns were observed for any of the metabolite subfractions; however, total recovered radioactive steroid (polar plus non-polar) formed a decreasing concentration gradient from point of entry of perfusate (PoM region) to point of exit (PrM region). These data support the conclusion that access to receptors by steroid ligands may be controlled by a balance between activating and inactivating pathways.(ABSTRACT TRUNCATED AT 400 WORDS)

Autocrine and paracrine role of steroids during spermatogenesis: studies in Squalus acanthias and Necturus maculosus

Due to a cystic mode of spermatogenesis and zonal testes, the spiny dogfish shark (Squalus acanthias) and salamander (Necturus maculosus) are advantageous for studying the relationship between steroidogenesis and germ cell development. Direct analysis of steroidogenic enzymes and steroid receptors in staged tissue samples, together with light and electron microscopic observation, suggests that androgens and estrogens produced by Sertoli cells or Leydig cells immediately before or after spermiation serve as intratesticular regulators of events specific to premeiotic stages of spermatogenesis. These correlative data are consistent with limited observations in mammalian testis and provide a conceptual framework for direct testing of functional interactions between spermatogenesis and steroidogenesis in future studies.

Culture of intact Sertoli/germ cell units and isolated Sertoli cells from Squalus testis: I. Evidence of stage-related functions in vitro

As part of an ongoing program of research using the testis of the dogfish shark (Squalus acanthias) to characterize morphologic and functional changes during spermatogenesis, we have developed procedures for culturing intact spermatocysts (germ cell/Sertoli cell clones) and isolated Sertoli cells from premeiotic, meiotic, and postmeiotic stages of development. Phase contrast and light microscopy confirmed the stage and cellular composition of spermatocysts and showed that they retained their closed, spherical configuration for at least 15 d in culture. Stage-related variations in [3H]thymidine incorporation (premeiotic much greater than meiotic = postmeiotic) were observed, a pattern that was the same quantitatively and qualitatively after one or seven days of culture. [3H]Leucine-labeled protein synthesis was twofold greater in cultures with premeiotic spermatocysts than in cultures with more mature stages, whether medium or cysts were analyzed. Sertoli cells isolated from spermatocysts of different stages differed in size, shape, cytological appearance, ability to form flattened monolayers, and rate of DNA synthesis. One day after seeding, [3H]thymidine labeling of Sertoli cells corresponded to the pattern obtained with intact spermatocysts (premeiotic much greater than meiotic = postmeiotic); however, 7 days in culture effected a 40- to 200-fold increase in this parameter and altered the stage-dependent pattern (premeiotic = meiotic greater than postmeiotic). Also, when [3H]leucine-labeled macromolecules secreted by Sertoli cells from premeiotic versus meiotic stages were analyzed by polyacrylamide gel electrophoresis (PAGE), banding patterns differed. Initial results demonstrate the feasibility and potential of this in vitro system for studying qualitative and quantitative changes during spermatogenesis.

Sites of action of local estradiol feedback mechanism in the frog (Rana esculenta) testis

The direct effect of estradiol on testicular androgen biosynthesis was studied in the frog, Rana esculenta, measuring progesterone, 17 alpha-OH-progesterone, androstenedione, and androgens (T + DHT) in supernatants and testes incubated (6 hr, 15 degrees) with estradiol alone (10(-6) M) or in combination with crude pituitary homogenate (1 pituitary equivalent/tube). Estradiol, either alone or in combination with pituitary homogenate, induced decreases of 17 alpha-OH-progesterone, androstenedione, and androgens but was ineffective in modulating progesterone levels. Pituitary homogenate was effective in inducing a significant increase of androstenedione and androgens but was ineffective in modulating both progesterone and 17 alpha-OH-progesterone production. It is concluded that estradiol acts by decreasing the activity of steroidogenic enzymes starting from 17 alpha-hydroxylase, while pituitary homogenate does not affect the 17 alpha-hydroxylase activity, but it acts starting from 17,20-lyase.

Shark testis model: stage-dependent functions and the regulation of spermatogenesis

In mammals, a single Sertoli cell nurtures 3-4 successive generations of germ cells. Thus, it is not possible to study this cell type at a single spermatogenic stage. In the dogfish shark Squalus acanthias, a single cohort of Sertoli cells remains associated with a germ cell clone throughout its development. Moreover, different germ cell stages are topographically segregated within the testis and can be easily staged by transilluminationmicroscopy. Recently, we have developed methods for the isolation and culture of spermatocysts (Sertoli/germ cell units) and Sertoli cells only from pre-meiotic, meiotic, and post-meiotic stages of germ cell development. Here, we present data that illustrate the feasibility of using the Squalus testis model for characterizing stage-related biochemical changes in Sertoli cells.

Role of the sertoli cell in spermatogenesis: TheSqualus testis model

In the dogfish sharkSqualus acanthias different germ cell stages are topographically segregated within the testis. Using this species we have developed methods for the isolation and culture of Sertoli cells from premeiotic, meiotic and post-meiotic stages of spermatogenesis and present preliminary evidence for stage-dependent variations in cell morphology and behavior, thymidine incorporation, protein synthesis and steroidogenesis. The goal of future studies is to determine how maturational changes are regulated in Sertoli cells and, in turn, to elucidate Sertoli cell-germ cell interactions.

Regulation of spermatogenesis: the shark testis model

Spermatogenesis is a unique developmental sequence dependent on FSH and androgen. Due to the complex organization of the mammalian testis, however, mechanistic details of regulation are largely unknown. Using the dogfish shark (Squalus acanthias) in which there is a cystic mode of spermatogenesis and a topographic separation of different germ cell stages within the testis, we have obtained new information of general relevance on stage-related biochemical and morphological changes and have proposed a model in which steroids serve as parahormonal regulators of the spermatogenic progression. In addition, techniques developed for culturing staged spermatocysts (intact Sertoli/germ cell units) and isolated, staged Sertoli cells demonstrate the usefulness of this model for studying spermatogenic regulation under defined conditions in vitro.

Nuclear acceptor sites for estrogen-receptor complexes in the liver of the turtle, Chrysemys picta. I. Sexual differences, species specificity and hormonal dependency

Hepatic estrogen receptors (ERs) of the female turtle, Chrysemys picta, when complexed with [3H]estradiol ([3H]E2), were shown to bind specifically to liver chromatin isolated from the same species. The binding of the [3H]E2 receptor complex to chromatin requires both the steroid ligand and the receptor protein. Maximal binding occurred within 60-70 min of incubation at 4 degrees C in a Tris buffer containing 0.1 M KCl. The binding of the [3H]E2 receptor complex to intact chromatin was saturable, whereas the binding to turtle or calf thymus DNA remained linear. Scatchard analyses revealed more estrogen receptor binding sites on hepatic chromatin isolated from female turtles than that prepared from the males (binding capacities: female chromatin = 67.9 +/- 6.8 fmol/mg DNA equivalent; male chromatin = 28.5 +/- 2.5 fmol/mg DNA equivalent). Furthermore, the [3H]E2 receptor complex was bound with a higher affinity to female chromatin than to male chromatin (association constants: female chromatin = 11.7 +/- 2.7 X 10(10) M-1; male chromatin = 2.5 +/- 0.7 X 10(10) M-1). In contrast to turtle hepatic [3H]E2 receptors, ERs in rat liver or mouse uterine cytosol exhibited little binding affinity for hepatic chromatin isolated from the turtle. Tissue specificity was demonstrated in the interaction of the [3H]E2 receptor complex and chromatin; high affinity, saturable binding of the [3H]E2 receptor complex was only observed on chromatin isolated from the liver but not on those prepared from the heart, kidney and muscle. A 3- to 4-fold increase in the number of hepatic chromatin [3H]E2 receptor binding sites was observed in 21-day ovariectomized or hypophysectomized female (capacities = 209.3 +/- 6.1 and 270 +/- 10.1 fmol/mg DNA equivalent, respectively). It is postulated that [3H]E2 receptor binding sites on the chromatin of intact females are partially 'masked', and removal of a gonadal and/or pituitary factor(s) unveils additional binding sites on the female chromatin. This paper is first to report the presence of high affinity, species- and tissue-specific acceptor sites on the liver chromatin of a reptilian species. The fact that the levels and properties of these acceptor sites are dependent on the sex and hormonal state of the animal suggests that they may play a role in the regulation of hepatic estrogen responsiveness and vitellogenesis in this species.

Molecular mechanism of steroid hormone action during aging. A review

The application of immunochemistry coupled with genetic engineering techniques has helped greatly in the understanding of the molecular mechanism of steroid hormone action. Particularly, the recent observations on nuclear localization of steroid receptor proteins and the interaction of the steroid-receptor complex with the genome have provided much insight into the whole pathway of steroid hormone action. Despite the large amount of data accumulated over the years on the mechanism of steroid action in general, relatively little is known about the changes occurring in the action of steroid hormones during aging. However, there is some evidence of a decreased responsiveness of target tissues to steroid hormones during senescence. In the light of recent progress in steroid research, an attempt has been made in this article to discuss the alterations that occur at different steps of steroid action as a function of age.

Dynamics of cortisol receptor activity in the gills of the brook trout, Salvelinus fontinalis, during seawater adaptation

Injection of cortisol into freshwater-adapted brook trout caused a rapid increase in plasma cortisol and a significant drop in plasma osmolality, thyroxine (T4), and chloride concentrations, but a nonsignificant drop in plasma triiodothyronine (T3). Concomitantly, cortisol cytosolic receptor activity decreased and cortisol nuclear extract receptor activity increased significantly. Transfer of brook trout into 30% seawater evoked a significant rise in plasma cortisol, osmotic, and chloride concentrations and a significant drop in plasma T4 and T3. Cortisol cytosol receptor activity rapidly dropped following entry into seawater, and cortisol nuclear extract receptor activity rose significantly in a manner similar to the effects of the injection of cortisol. Although there was a lack of correlation between the cytosol cortisol concentration and the cytosol receptor concentration, a significant and positive correlation occurred between the nuclear extract cortisol concentration and the nuclear extract cortisol receptor activity. This positive correlation may reflect an important role for the putative nuclear receptor. These results support the hypothesis that cortisol has an important role in the adaptation of brook trout to the marine environment.

A novel steroid-binding protein in the testis of the dogfish Squalus acanthias

In an earlier study, we identified and characterized a testicular estrogen receptor in the spiny dogfish (Squalus acanthias); however, in this species estrogen receptors were located exclusively in nuclear subfractions. We describe here a nonreceptor, sex hormone-binding protein (SBP) present in Squalus testicular cytosol and distinguishable in its physicochemical characteristics from both the estrogen receptor and serum SBP of the same species. Cytosol (100,000g supernatant) was prepared by differential centrifugation of testicular homogenates and incubated with [3H]estradiol (E2) or [3H]testosterone (T) (10-15 nM +/- 100-fold excess radioinert competitor) to determine total and nonspecific bound radioactivity. The testicular SBP had a broad specificity: E2 = T greater than progesterone greater than 5 alpha-dihydrotestosterone greater than estrone, but diethylstilbestrol was not an effective competitor. It displayed a high affinity for both E2 and T (Kd = 2.2-2.5 X 10(-9) M), sedimented at 8-10 S in both low- and high-salt sucrose gradients, and migrated more slowly than BSA during polyacrylamide disc gel electrophoresis. The testicular SBP-E2 complex was relatively stable (t1/2 = 160 min) compared to the serum SBP-E2 complex (t1/2 = less than 30 min). The testicular SBP was not found in nuclear subfractions nor did it bind to DNA-cellulose affinity columns. Its intratesticular distribution was stage-dependent: Zone III (mature spermatids) greater than Zone II (spermatocytes) greater than Zone I (stem cells and spermatogonia). Moreover, increased binding activity corresponded exactly to the hypertrophy and differentiation of Sertoli cells in the same zones, pointing to this cell as the possible site of SBP synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

The presence of corticosteroid receptor activity in the gills of the brook trout, Salvelinus fontinalis

Gill tissue from brook trout was examined for the presence of cortisol receptors. Both cytosolic and nuclear preparations from the gills manifested high equilibrium association constants (Ka) and low maximum binding capacities (Nmax) indicative of high-affinity and low-capacity receptor activity (cytosol: Ka = 0.31 +/- 0.02 X 10(9)/M, Nmax = 223.9 +/- 22.8 fmol/mg protein; nuclear extract: Ka = 0.02 +/- 0.003 X 10(9)/M, Nmax = 424.6 +/- 96.3 fmol/mg protein). Gel permeation (Sephacryl S-300) column chromatography gave two incompletely separated peaks at 326,000 and 189,000 Da and Stokes radii of 5.96 and 4.81 nm using [3H]triamcinolone acetonide and only one peak at 219,000 Da and 5.4 nm using [3H]cortisol. The binding of the synthetic compounds, triamcinolone acetonide and dexamethasone, appears to be different from that of the natural steroid, cortisol. The receptor activity appears to be highly specific for cortisol since cortisone and 11 beta,17 alpha,21-trihydroxy-4-pregnen-3,20-dione-21-phosphate bind with much lower affinity. The gill tissue cytosol fractions had the highest cortisol-binding activity, followed by liver, intestine, and muscle. The association constants for the liver, intestine, and muscle were the same order of magnitude as that for the gill. These results are consistent with the concept of nonmembrane steroid receptors of target organs.