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Biomedical subjects

L T Samuels

Publications and source records attributed to L T Samuels.

11 recordsLinked to original sources
PubMed1979

The testicular estrogen receptor system in two strains of mice differing in susceptibility to estrogen-induced Leydig cell tumors.

Cytosol obtained from cryptorchid testes of tumor-susceptible BALB/c and resistant C3HBi (Z) mice both bound 17 beta-estradiol (E2) and diethylstilbestrol (DES) specifically. The dissociation constant (Kd) of this binding component (RE) for E2 was determined to approximate 5 x 10(-9) M. Gel filtration of cytosols resulted in a significant increase in the binding constant (Kd approximately 3 x 10(-10) M) with the majority of the complex migrating in the 7-8S area after sucrose gradient centrifugation. Incubation of either untreated or gel-filtered cytosol with [3H]DES resulted in considerable nonspecific binding appearing in the 4S region in a low salt sucrose gradient. This 4S binding of [3H]DES was not inhibited by the addition to the incubation mixtures of a 100-fold excess of either E2 or DES, while the lesser peak at 7-8S as well as the major 7-8S peak formed with E2 were inhibited by both. In vitro translocation of the cytosol RE to the nucleus was demonstrated in both mouse strains using either estrogen. Quantitation of the in vivo translocation, employing the exchange method after a single injection of 2.5 micrograms E2/mouse, revealed a rapid increase in cytoplasmic receptor content accompanied by a concomitant increase in nuclear receptor content. Greater nuclear receptor content was identified in nuclei from BALB/c mice than in those from Z animals 45 min after injection of E2. The binding behavior of E2-RE complexes to nuclei was studied by the KCl extraction method. The percent extracted from the nuclei in the Z strain was significantly greater than that in the BALB/c at all concentrations of KCl tested. Essentially 100% of the RE was extracted from nuclei of Z animals at 0.4 M KCl, while nuclei of BALB/c mice retained 35-40% even in 2 M KCl. Cross-over experiments in a cell-free system suggested that the difference in binding was due to differences in chromatins rather than in nuclear estrogen-receptor complexes. The greater nuclear receptor content and stronger binding of nuclear receptor to chromatin might explain why estrogen-induced phenomena, including neoplastic transformation occur to a much greater degree in the BALB/c strain than in the Z strain of the mouse.

Animals↗
PubMed1978

Electron spin resonance studies of erythrocytes from patients with Duchenne muscular dystrophy.

The membrane organization of the erythrocytes from patients with Duchenne muscular dystrophy was studied by means of electron spin resonance. The fluidity of the membrane near the polar region of Duchenne muscular dystrophy erythrocytes was similar to that of normal erythrocytes. The membrane environment in the nonpolar region, however, was quite different from that of normal erythrocytes, judged by the spectra with 2-(14-carboxytetradecyl) - 2 - ethyl - 4,4 - dimethyl - 3 - oxazolidinyloxyl as probe. The temperature dependence of the ratio of the line height of central field to that at the low field showed two inflection points in normal erythrocytes at pH 7.4 (13.5 degrees -16.5 degrees and 37.5 degrees -40.5 degrees C, respectively) but the inflection point in the lower temperature range was not detected in Duchenne muscular dystrophy erythrocytes. When pH was varied, an abrupt decrease in the ratio was observed at pH 5.9-5.6 in normal erythrocytes whereas there was a gradual decrease over the range of pH from 6.6 to 5.0 in Duchenne muscular dystrophy erythrocytes. The rate of reduction of the radical 2-(3-carboxypropyl)-4,4-dimethyl-2-tridecyl-3-oxazolidinyloxyl by ascorbate in normal erythrocytes was faster than that in Duchenne muscular dystrophy erythrocytes. Treatment of both erythrocytes with phloretin markedly reduced the rate of reduction by ascorbate and eliminated the difference in the two types of erythrocyte. These results indicate that in Duchenne muscular dystrophy the erythrocyte membrane is involved as well as the muscle cell.

Adolescent↗
PubMed1978

Evidence of a small molecule in mouse Leydig cell tumors which inhibits the conversion of estrogen receptor from 4S to 5S.

The activation process of cytosol estrogen receptor (RE) from mouse Leydig cell tumors was investigated. When RE from tumors which were affected in their growth by estrogen was heated at 25 C for 30 min in high ionic strength buffer it was converted from native 4.0S to a transformed (5.3S) state. Dialysis of the cytosol from these tumors at 0-4 C in either the presence or absence of estradiol also resulted in conversion to 5.3S when estradiol was added before the sample was applied to the sucrose density gradient. When the dialyzed cytosol was applied to a sucrose density gradient without estradiol, the peak of estrogen binding capacity tested by adding E2 to the fractions from the gradient, occurred at approximately 4S. The dialysate of cytosol had an inhibitory effect on activation by warming. Dialysis of cytosol in the presence of estradiol enhanced the translocation of estradiol-receptor complex to nuclei. Molecular weight (approximately 128,000) and frictional coefficient (f/f0 1.62) of the estrogen-receptor complex dialyzed in the presence of high salt concentration were identical with those of warmed RE complex, but quite different from the native RE (approximately 73,000 daltons, frictional coefficient 1.48). This evidence indicates the presence in the cytosol of one or more small molecules which, when noncovalently bound to RE, inhibit the conversion of the native cytosol RE to the transformed state R'E2RE, having an additional protein unit.

Animals↗
PubMed1978

Localization of delta4-5alpha-reductase in immature rat testes.

Testes of 29-35-day-old rats were separated into seminiferous tubules and interstitial tissue by collagenase treatment and examined by incubation studies with radioactive substrates. The activity of testosterone 5alpha-reductase/g protein in the interstitial tissue was 37 times greater than that in the tubules. The site of formation of 5alpha-reduced C21- and C19-steroids from progesterone was found to be primarily in the interstitial tissue. In the interstitial tissue, testosterone 5alpha-reductase activity, which was stimulated 300-fold by the addition of NADPH, was localized in the microsomal fraction (8,000-105,000 X g precipitate). NADPH was five times as effective a hydrogen donor as NADH when the washed microsomal fraction was the source of the enzyme. The formation of 5alpha-reduced C21- and C19-steroids from pregnenolone and progesterone was demonstrated in the microsomal fraction of interstitial tissue. These results indicate that in 29-35-day-old rat testes, 5alpha-reduction of C19-delta4-3-ketosteroids and the formation of 5alpha-reduced C21- and C19-steroids from pregnenolone take place largely in the microsomes of interstitial tissue.

3-Hydroxysteroid Dehydrogenases↗
PubMed1978

The possible roles of membrane organization in the activity of androgen biosynthetic enzymes associated with normal or tumorous mouse Leydig cell microsomes.

The enzymes involved in conversion of pregnenolone to testosterone in Leydig cell tumors showed a wide distribution among smooth endoplasmic reticulum (SER), rough endoplasmic reticulum (RER), and cytosol, while these enzymatic activities in normal testes were associated primarily with smooth endoplasmic reticulum. Progesterone, used as a substrate in the presence of an NADPH-generating system, was metabolized to androstenedione and finally to testosterone by microsomes from some strains of tumor which did not form testosterone from exogenous labeled androstenedione. Treatment of microsomal membranes from normal testes with 0.1 M Ca++ and Mg++ caused a marked decrease in 17 beta-dehydrogenase activity, measured as conversion of exogenous [3H]androstenedione to [3H]-testosterone, without serious effects on activities of 3 beta-ol-dehydrogenase or 17 alpha-hydroxylase. Studies of initial velocity kinetics showed that treatment with magnesium ion resulted in a marked reduction in affinity of androstenedione for 17 beta-dehydrogenase while the maximum velocity was the same as in untreated microsomes. Also, experiments using [14C]progesterone and [3H]androstenedione simultaneously as substrates demonstrated that treatment with Mg++ ion made it more difficult for exogenous [3H]androstenedione to reach the active site of 17 beta-ol-dehydrogenase than [14C]androstenedione formed in the microsomal membrane from [14C]progesterone. Microsomal proteins were more easily solubilized and 3 beta-ol-dehydrogenase was more severely influenced by Mg++ ion in tumor membranes than in normal microsomes.

17-Hydroxysteroid Dehydrogenases↗
PubMed1978

DNA synthesis and DNA polymerase activity in Leydig cells of diethylstilbestrol-stimulated mouse testes.

Using a modification of the collagenase dispersion method of Dufau et al., we examined changes in DNA synthesis produced by estrogens in the interstitial cells of mice that develop malignant Leydig cell tumors after prolonged estrogen administration. Previous work in cryptorchid mice indicated that during continuous estrogen administration [3H]thymidine incorporation into DNA rises to a maximum in 3 to 4 days and then falls to approximately base levels within 2 to 3 weeks. This was confirmed both in Leydig cell concentrates of estrogen-treated mice after either injection with [3H]thymidine or incubation with [3H]thymidine in vitro. This DNA synthesis was blocked by hydroxyurea. DNA synthesis in cells of estrogen-treated BALB/c mice of the Huseby substrain, which have a high incidence of Leydig cell tumors, was 5 to 11 times that in untreated controls. Cells from estrogen-treated C3H/Bi mice, which have a low incidence of Leydig cell tumors, showed only a 2- to 3-fold increase. In the Huseby substrain the rise of DNA synthesis is a peak and subsequent recession were paralleled by a rise and fall in DNA polymerase alpha activity. DNA polymerase beta did not show this variation. In C3H/Bi mice, neither polymerase showed significant change. The evidence suggests that the early estrogen-stimulated DNA synthesis is probably replicative and is associated with increased DNA polymerase alpha activity.

Animals↗
PubMed1977

Lack of influence of hypophysectomy on estrogen-induced DNA synthesis in Leydig cells of BALB/c mice.

In mice of strains susceptible to Leydig cell tumor induction, treatment with estrogens induced a "spurt" of DNA synthesis within the first few days. This synthetic activity generally subsided, until areas of Leydig cell hyperplasia developed several months later. Autoradiographic and quantitative biochemical studies indicated that in BALB/c mice this initial DNA synthetic activity occurred in the absence of the hypophysis and apparently was the result of effects of estrogen directly on Leydig cells. Although hypophysectomy inhibited sperm maturation, [3H]thymidine incorporation into spermatogonia was reduced only slightly 2 weeks after surgery, as was the induced DNA spurt in the interstitial tissues.

Animals↗
PubMed1976

Effects of trypsin and phospholipases A2 and C on enzyme organization in testis microsomes.

Pregnenolone and progesterone concentrated in the microsomal fraction of cryptorchid mouse testis compared with mitochondria and cytosol. While the concentrating mechanisms had high capacity and low association constants the effect did not seem to be due to nonspecific solubility in the lipid components since 17-hydroxyprogesterone, dehydroepiandrosterone, androstenedione and testosterone did not show differential concentration. Also digestion with phospholipases A2 and C to the point where most of the phospholipids were specifically split, only lowered the differential binding of pregnenolone and progesterone by less than half. Trypsin had a greater effect, short digestion at 0 degrees C lowering the specific binding to 35-40% and decreasing the steroid dehydrogenases to a similar extent. The members of the mixed function oxidase system in the testis microsomes were particularly sensitive to trypsin, cytochrome P-450 and, as a consequence, 17alpha-hydroxylase and 17, 20-lyase activity being eliminated under tha same conditions while liver microsomal cytochrome P-450 was hardly affected. Bonds split by trypsin seem to play a more important role in the hydroxylase activity of testis microsomes than in the hepatic system.

Androstenedione↗