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Biomedical subjects

L J Valenta

Publications and source records attributed to L J Valenta.

At least 73 records · Page 4Linked to original sources
PubMed1978

Luteinizing hormone secretion and gonadotropin releasing hormone binding in heifer and steer anterior pituitaries.

Luteinizing hormone (LH) release and tissue content were studied in explanted bovine pituitaries from heifer and steer during superfusion in vitro. Compared to steer, heifer pituitaries contained significantly more LH and released more LH into the incubation medium. Quantitative response in LH release to gonadotropin releasing hormone (GnRH) stimulation was about equal in heifer and steer, but relative increase was more pronounced in steer. Specific 125I-GnRH binding to dispersed anterior pituitary (AP) cells and isolated plasma membranes was also analyzed. Concentration dependent binding curve of 125I-GnRH to dispersed cells exhibited sigmoid characteristics suggesting positive cooperativity. There was a sex dependent difference, the binding curve for heifer being shifted to the left and reaching saturation at lower GnRH concentrations than that for steer. "Multisigmoid" concentration dependent GnRH binding curves were obtained using isolated plasma membranes, revealing the presence of multiple binding sites. One of the binding sites, present in heifer, was absent in the steer derived materials, but could be induced by pretreatment of the steer plasma membranes with 17-beta estradiol as low as 50 pg/ml. It is concluded that the differences in GnRH binding may be responsible, at least in part, for the observed differences in LH secretion pattern between heifer and steer.

Animals↗
PubMed1978

Binding of gonadotrophin releasing hormone (GnRH) by bovine anterior pituitary plasma membranes and purified GnRH receptor protein (GnRH.R).

[125I]-(GnRH) concentration dependence binding curves using isolated bovine anterior pituitary plasma membranes, intact and solubilized, and purified GnRH receptor protein, are compared. In all instances the concentration dependence binding curves had a stepwise character here interpreted as multisigmoid, with several steep increases and plateaus. These curves are compatible with the existence of several binding sites for GnRH. Purification of the GnRH receptor protein (GnRH.R) resulted in about 500 000-fold increase of binding activity and yielded a single protein species on polyacrylamide gel electrophoresis in SDS, of estimated molecular weight 60 000. Similarity of GnRH binding by the purified protein with that of intact and solubilized plasma membranes suggested that a single protein was responsible for the binding in each instance. Thus heterogeneity of GnRH binding is likely attributable to phase transitions of a single receptor protein into different allosteric forms. The data suggest that positive cooperativity is involved in the studied system.

Animals↗
PubMed1977

Microfollicular thyroid carcinoma with amyloid rich stroma, resembling the medullary carcinoma of the thyroid (MCT).

A human thyroid tumor is described which, on light microscopy, exhibited the features of medullary carcinoma of the thyroid (MCT). The cells were arranged in solid lobules or trabeculae, and the stroma was abundant and gave positive reaction for amyloid as assessed by congo red, crystal violet and thioflavin T stains. However, there was microfollicular differentiation in certain portions of the tumor even where the tumor was invasively growing. On electron microscopy, numerous microfollicles were identified even where unsuspected by light microscopy. There were junctional complexes, the cells possessed well developed rough endoplasmic reticulum, prominent Golgi and numerous dense bodies obviously derived from the Golgi vesicles, which were of the same morphology as "secretory" granules described previously by some authors in MCT. However, we find this kind of cytology typically in microfollicular thyroid carcinomas. Presence of about 100 A thick fibrils in the stroma was consistent with histochemically positive amyloid. The biochemical data were compatible with the differentiated follicular cell origin of the tissue. The homogenate contained poorly iodinated thyroglobulin, and thyroid peroxidase activity. Calcitonin was undetectable by a sensitive radioimmunoassay. It is concluded that this tumor was follicular thyroid carcinoma with amyloid rich stroma. The presence of amyloid and dense bodies with homogenous electron dense contents is insufficient for making conclusions about histogenesis of thyroid tumors. The so called MCT with amyloid stroma probably represents a heterogenous group of thyroid tumors, at least some of them derived from follicular epithelium.

Adenocarcinoma↗
PubMed1977

Ultrastructure and biochemistry of thyroid carcinoma.

Thirty-two thyroid tumors, 9 benign, 23 malignant, and 12 samples of normal thyroid tissue were examined by light and electron microscopy. Thyroglobulin content was also measured in the tissues and, in a limited number of cases, enzymatic activities were determined, such as thyroid peroxidase-iodinase, acid protease, and deiodinase. The presence of significant amounts of 19S, 27S and 12S thyroglobulin was well correlated with the ability of the tumors to accumulate radioiodine. It is suggested that the presence of thyroglobulin be used as a marker of potential function of thyroid carcinoma. Two types of ultrastructural changes were observed in thyroid carcinoma. The first one was interpreted as accompanying the progressive loss of function of thyroid tumors, and was represented by the modifications of highly specialized structures such as RER, lysosomal dense bodies, colloid, etc. The second one is suspected to reflect the malignant transformation of the follicular cell. This concerned namely the nuclei, mitochondria, and intracytoplasmic inclusions. These changes may have a diagnostic value since they were not observed in benign conditions.

Adenocarcinoma↗
PubMed1977

Ovarian dysgenesis due to 45 X, 0/46 dic (X) mosaicism.

A 16 year old girl was evaluated for short stature, primary amenorrhea, and lack of development of secondary sex characterisics. She did not have the classical phenotypic signs of Turner's syndrome. However, she was short, had infantile genitalia and the adnexa were not palpable. There was a minor bone malformation and no signs of visceral abnormalities. The hormonal studies showed hypergonadotropic hypogonadism and borderline hypothyroidism. The rest of the endocrine functions was normal. The Barr bodies on the buccal smear were decreased and in part abnormal, large or bipartite. The karyotype showed mosaicism of about equal proportions of 45 X, 0/46, X, dic (X). The large dicentric chromosome was due to the end to end fusion of two X chromosomes by their short arms. Sequential binding studies were performed and failed to document any loss of genetic material of the dicentric X. It is speculated that the fusion of X chromosomes during an early mitotic division was responsible for the 45 X, U cell line, and that the short stature and gonadal dysgenesis in this patient was due to the presence of the 45 X, 0 line.

Adolescent↗
PubMed1977

Iodopeptides from human thyroglobulin.

Human thyroglubulin labelled in vivo by 125I was purified from eight different thyroid glands including normal thyroid tissue, thyrotoxic goitre and euthyroid multinodular goitre. The purified protein was cleaved with cyanogen bromide (CNBr) and the resulting peptides were separated by column chromatography and ion exchange chromatography. Reproducible elution profiles of both protein and iodine were obtained. However, the distribution of iodine depended on the iodine content of the intact thyroglobulin. Small CNBr peptides seemed to be preferentially iodinated, but with a limited capacity. With higher degrees of iodination, larger peptides became richer in iodine. This suggests sequential iodination of the thyroglobulin molecule. The mixture of small peptides was digested by trypsin. Two iodopeptides were identified in this material by peptide mapping and they had identical migration in thyroglobulins of different origin. One of them was purified by ion exchange chromatography and high voltage electrophoresis. Analogous amino acid composition was obtained for the iodopeptide purified from two different thyroglobulins. The data indicates that thyroglobulin iodination occurs in specific portions of the polypeptide chain and probably in a sequential manner.

Amino Acid Sequence↗
PubMed1977

Electron microscopy of clear cell thyroid carcinoma.

Three thyroid carcinomas composed in part or entirely of clear cells were studied by light and electron microscopy, and thyroglobulin content was determined by biochemical methods. Clear cells have been found in follicular and papillary thyroid carcinomas and in undifferentiated carcinomas. The clear (wasserhelle) appearance of the cytoplasm was due to the accumulation of glycogen. The major ultramicroscopic features of the clear cells were the presence of glycogen granules, the decreased amounts of rough endoplasmic reticulum, the increased amounts of free ribosomes arranged in polysomes, a hypertrophic Golgi apparatus, and a sparsity of dense bodies of lysosomal character. It is hypothesized that the intracellular accumulation of glycogen may be a result of a selective loss of the peptide portion of thyroglobulin, and may influence the degree of biochemical differentiation and the natural course of the tumors.

Adenocarcinoma↗
PubMed1977

A syndrome of functional hypogonadotropic hypogonadism and sterility in a male with elevated serum estradiol.

A 36-year-old male complaining of impotence was examined. He was a genotypic male. Phenotypically, he exhibited signs of long-standing estrogen excess, such as feminine body build, gynecomastia, and varicose veins. His testes were soft and borderline small, and his prostate was small and soft. However, he had a normal-sized penis, normal male hair distribution, normal sense of smell, and normal intelligence. The laboratory data were compatible with mild hypogonadotropic hypogonadism. Serum estradiol (E2) levels were consistently elevated. The patient had azoospermia and a decreased semen volume. Inappropriately low levels of luteinizing hormone and follicle-stimulating hormone responded normally to gonadotropin-releasing hormone and clomiphene citrate. Levels of both testosterone (T) and E2 increased dramatically after prolonged clomiphene medication and in response to human chorionic gonadotropin. There was no change in either T or E2 levels in response to manipulations of the pituitary-adrenal axis. It is concluded that the elevated E2 level was responsible for suppression of gonadotropins which, in turn, caused mild hypogonadism and sterility in this patient. According to the stimulation tests, the source of the elevated E2 levels was testicular.

Adolescent↗
PubMed1976

Thyroid peroxidase, thyroglobulin, cAMP and DNA in human thyroid.

Tissues from normal thyroid, euthyroid multinodular goiter, toxic goiter, Hashimoto's thyroiditis, thyroid adenoma, and carcinoma were examined for their content of deoxyribonucleic acid (DNA), thyroid peroxidase activity (TPA), thyroglobulin (TG), and adenosine 3',5'-cyclic monophosphate (cAMP). Compared with normal thyroids DNA was increased in the neoplastic tissues and decreased in euthyroid multinodular goiter. Quantitative changes of thyroglobulin were observed, especially in the thyroid tumors, and, in one case, immunoreactive 4S thyroglobulin-like protein was identified in the absence of 19S. TPA was grossly elevated in toxic goiter. This may be of significance in the pathogenesis of Graves' disease. TPA remained elevated even after adequate control of hyperthyroidism by preoperative PTU treatment. The cyclic AMP concentration in toxic goiter did not statistically differ from normal. This may indicate that extrathyroidal regulatory factors have a lesser role in the genesis and perpetuation of Graves' disease than otherwise believed. Cyclic AMP is known to exert a negative influence on tissue growth, and low concentrations in neoplasia have been reported. The values in the thyroid tumors studied were elevated, requiring further explanation.

Cyclic AMP↗