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Biomedical subjects

I B Fritz

Publications and source records attributed to I B Fritz.

At least 91 records · Page 5Linked to original sources
PubMed1977

Stimulation by androgens of the production of androgen binding protein by cultured Sertoli cells.

The formation of androgen-binding protein (ABP) by cultured Sertoli cells, prepared from testes of immature rats, is increased when androgens or follicle-stimulating hormone (FSH) are present in the medium. Testosterone and 5alpha-dihydrotestosterone are equally effective in stimulating the synthesis and secretion of ABP, but non-androgenic steroids examined (progesterone, 17beta-estradiol and corticosterone) are without influence. Maximal increases are observed when androgens are added at the time of cell plating. Cells maintained in culture medium devoid of hormones become progressively less sensitive to subsequent addition of testosterone or FSH. Data are discussed in relation to the sites of androgen requirements for spermatogenesis.

Androstane-3,17-diol↗
PubMed1976

Site at which FSH regulates estradiol-17beta biosynthesis in Sertoli cell preparations in culture.

Sertoli cells were isolated from testes of 20-day-old rats and were maintained in primary culture. The ability of these cells to synthesise estradiol-17beta from a variety of exogenous substrates, progesterone, testosterone,androstenedione, 19-hydroxyandrostenedione and 19-hydroxytestosterone in the presence and absence of follicle-stimulating hormone (FSH) was examined. In the presence of each of the substrates alone for 24 h the rate of estradiol-17beta synthesis was very low. FSH (NIH-FSH-S11, 5 mug/ml) stimulated estradiol-17beta synthesis 75-fold when added to medium containing testosterone (5 X 10(-7)M) but caused only marginal stimulation when added to medium containing progesterone (5 X 10(-7) M). Both FSH and dibutyryl cyclic AMP (bu2cAMP) stimulated the conversion of each of the substrates, androstenedione, 19-hydroxyandrostenedione and 19-hydroxytestosterone to estradiol-17beta, and the effects were similar to those observed in the presence of testosterone. These data indicate that, under the culture conditions employed, progesterone is not an effective substrate for conversion to estradiol-17beta by Sertoli cells. Estradiol-17beta synthesis was stimulated by FSH in the presence of the C19 steluences the conversion of androgens to estrogens, either directly or indirectly, at the aromatisation step (i.e. the conversion of 19-hydroxylated androgens to estrogens).

Androstenedione↗
PubMed1976

FSH stimulation of DNA synthesis in Sertoli cells in culture.

The incorporation of [2H]thymidine into nuclear DNA was investigated in cultured Sertoli cells prepared from testes of 20-day-old rats. Addition of follicle-stimulating hormone (FSH) or dibutyryl cyclic, 3',5'-adenosine monophosphate (DBCAMP) to the culture medium greatly increased incorporation, expressed either as total amounts of [3H]thymidine incorporated per mug DNA or as the percentage of Sertoli cells with labeled nuclear DNA. No stimulation was observed in cells cultured in the presence of testosterone, insulin or cyclic 3',5'-GMP (cGMP). Light and electron microscopic autoradiographic analysis was employed to establish the identity of Sertoli cells having labeled nuclear DNA. Contaminating spermatogonia, which also took up labeled [3H]thymidine, were excluded from cell counts. In addition, Sertoli cells prepared from testes of irradiated 20-day-old germinal cell depleted rats were also observed to incorporate more [3H]thymidine into nuclear DNA when cultured in a chemically defined medium in the presence of FSH. DNA synthesis was abolished by prior treatment of cells with cytosine arabinoside. In separate experiments, the incorporation of [3H]thymidine into DNA of peritubular myoid cells was shown to be independent of FSH or dbcAMP.

Animals↗
PubMed1976

Regulation by FSH and dibutyryl cyclic AMP of the formation of androgen-binding protein in Sertoli cell-enriched cultures.

Sertoli cell-enriched preparations from testes of 20-day-old rats were cultured in a defined medium in the presence and absence of FSH or dibutyryl cyclic AMP (dcAMP). Androgen-binding activity was assayed in the culture medium, and related to testicular androgen-binding protein (ABP). The production and secretion of ABP by the Sertoli cell-enriched preparation was increased after FSH or dcAMP treatment of the primary culture. It is concluded that ABP is produced by Sertoli cells. The possibility of involvement of other cell types in the testis in ABP production is discussed.

Androgens↗
PubMed1975

Effects of fasting on the control of fatty-acid synthesis in hepatoma 7777 and host liver. Role of long-chain fatty acyl-CoA,, the mitochondrial citrate transporter and pyruvate dehydrogenase activity.

The effects of fasting on the rate of fatty acid synthesis, the properties of the mitochondrial citrate transporter and on pyruvate dehydrogenase activity were investigated in "poorly-differentiated" tmorris hepatoma 7777 and in host liver preparations. The properties of the citrate transporter from hepatoma mitochondria were similar to those of host liver mitochondria, with the exception that the Km for the liver mitochondrial citrate transporter was 248 plus or minus 20 mu M while that in hepatoma mitochondria was less than 75 mu M. The acid-insoluble CoA content was 180 plus or minus 20 pmol/mg protein in the hepatoma and remained essentially unchanged in the fasted state, while the acid-insoluble CoA levels in livers from fed rats was 720 plus or minus 80 pmol/mg protein and were increased to 1050 plus or minus 50 pmol/mg protein during fasting. After a 36-h fast, the rate of lipogenesis and the percentage of pyruvate dehydrogenase present in the active form were each decreased by approximately 80% in host liver preparations. In contrast, the rate of lipogenesis by hepatoma slices did not decrease during fasting, and essentially all pyruvate dehydrogenase present was in the active form of hepatomas obtained from either fed or fasted animals. Implications concerning the identification of possible regulatory sites in the control of lipogenesis were discussed in relation to the above observations.

Acetyl Coenzyme A↗
PubMed1975

Synthesis of estradiol-17 beta by Sertoli cells in culture: stimulation by FSH and dibutyryl cyclic AMP.

Sertoli cells isolated from the testes of 18 to 20-day old rats synthesize estradiol-17 beta when grown in primary culture in the presence of testosterone (5 X 10(-7) M). After an initial lag phase of about 2 hours, follicle-stimulating hormone (FSH) stimulates synthesis of estradiol up to 50-fold, synthesis being approximately linear for 24 hours when medium is changed every 2-6 hours. Luteinizing hormone (LH) causes only a marginal stimulation, at concentrations consistent with contamination with FSH. Dibutyryl cyclic 3',5'-adenosine monophosphate (dbcAMP) (10(-4)M) mimicks the effect of FSH. No significant synthesis occurs in the absence of steroid substrate or in the presence of pregnenolone (5 X 10(-7) M). When cells are pre-incubated for 24 hours with FSH in the absence of testosterone, addition of testosterone results in an immediated increase in estradiol synthesis without a lag phase, suggesting that FSH or dbcAMP are capable of inducing the conditions necessary for stimulation in the absence of testosterone. These observations provide the first direct evidence of estradiol-17 beta synthesis by Sertoli cells from normal animals, and offer evidence that synthesis of this steroid is regulated at the level of the aromatizing enzyme system by FSH and cyclic AMP.

Animals↗
PubMed1975

Effects of follicle-stimulating hormone on cultures of Sertoli cell preparations.

Sertoli cell-enriched preparations were obtained by sequential enzyme treatment of testes of 18-20 day old rats, and were maintained in culture in a chemically defined medium. The addition of highly purified follicle-stimulating hormone (FSH) to cells immediately after preparation, or after 48 h in culture, elicited an increase in the level of cyclic adenosine 3',5'-monophosphate (cAMP) when incubated in the presence of 3-isobutyl-1-methylxanthine (MIX). Luteinizing hormone (LH) had no effect on the cAMP levels. The cells cultured in the presence of FSH or dibutyryl cAMP for 48 h incorporated more [3H]leucine into trichloroacetic acid (TCA)-insoluble material than did cells cultured in the basal medium. Cycloheximide abolished the amino acid incorporation into protein precipitated by TCA. The data demonstrate that the Sertoli cell is a target cell for FSH action, and indicate that added dibutyryl cAMP can duplicate the enhancement of amino acid incorporation into protein elicited by FSH.

Animals↗
PubMed1975

Structural changes inducted by follicle-stimulating hormone or dibutyryl cyclic AMP on presumptive Sertoli cells in culture.

Cells isolated from testes of 20-day-old rats, maintained in primary culture in a defined medium, are shown to respond to follicle-stimulating hormone or 3:5-cyclic AMP with characteristic morphological changes. No response is observed in cells treated with luteinizing hormone or 5-?AMP. The cells form a mono-layer, and have been identified as presumptive Sertoli cells structurally by identification of unique tight junctions in electron micrographs of the preparations, along with other ultrastructural properties characteristic of Sertoli cells in situ. These cells do not undergo mitosis. The presumptive Sertoli cells are shown to be morphologically and functionally different from peritubular fibroblasts grown in parallel cultures. Fibroblasts have high rates of mitosis, do not respond to follicle-stimulating hormone, and frequently form multilayers. Other information on the biochemical responses of the cells is cited, which supports the conclusion that the cultured cell preparations consist primarily of Sertoli cells.

Animals↗
PubMed1975

Cellular localization of 5alpha-reductase and 3alpha-hydroxysteroid dehydrogenase in the seminiferous tubule of the rat testis.

Seminiferous tubules isolated from normal adult rats converted (14C) testosterone to (14C) androstanediol and (14C) androstenedione as the major metabolites; (14C) dihydrotestosterone and (14C) androsterone were produced in lesser amounts. Tubules from immature rats (26-28 days of age) converted a higher proportion of (14C) testosterone to 5alpha-reduced products than did tubules from adult rats. Spermatocyte-enriched preparations contain 5alpha-reductase. The lower level of 5alpha-reductase activity in spermatid-spermatocyte preparations indicates that this enzyme is low or absent in spermatids. Sertoli cell-enriched preparations contain 5 alpha-reductase and a high level of 3alpha-hydroxysteroid dehydrogenase. The results show that spermatocytes and Sertoli cells have the capacity to metabolise (14C) testosterone to 5alpha-reduced products; dihydrotesterone is the major product formed by spermatocytes, whereas in Sertoli cells further metabolism to 5alpha-androstane-3alpha, 17beta-diol occurs.

Age Factors↗
PubMed1975

Hormonal requirements of the different cycles of the seminiferous epithelium during reinitiation of spermatogenesis in long-term hypophysectomized rats.

Restoration of testicular function in long-term hypo-physectomized rats given different hormonal treatments during the various cycles of the seminiferous epithelium was evaluated on the basis of the weights of testes, epididymides, and other accessory sexual glands, histological examination of testes, and determination of the numbers of spermatozoa/epididymis. The staput fractionation technique for the separation of classes of germinal cells was employed to provide a measure of the advancing front of pulse-labelled cells following the intratesticular administration of (3-H)thymidinemthe results suggested that during the first two cycles, in which spermatogonia develop into pachytene spermatocytes, either LH or testosterone alone was sufficient for partial restoration. During the third cycle of the seminiferous epithelium, LH and FSH were required to allow previously labelled pachytene spermatocytes to progress efficiently to stage 7 spermatids. Administration of LH alone during the final cycle was sufficient to permit stage 7 spermatids to develop into spermatozoa, provided LH plus H had been given during the previous three cycles. Injection of LH during the entire period and of FSH during the third cycle of the seminiferous epithelium was required to achieve Staput profiles characteristic of a normal advancing front of pulse-labelled cells, and to allow partial restoration of spermatogenesis. More complete restoration was obtained in rats given FSH and LH during the first three cycles but, with the doses employed, the number of spermatoza/testis remained subnormal. Efficient completion of each cycle of the seminiferous epithelium appeared to be hormone-dependent. The data are discussed in relation to the possibility that hormones may affect the general development of germinal cells in an indirect manner by their influence on Sertoli cell function.

Animals↗