Search PubMed⌕ Search

Biomedical subjects

J C Calvo

Publications and source records attributed to J C Calvo.

At least 37 records · Page 2Linked to original sources
PubMed1991

Differentiation of 3T3-L1 preadipocytes with 3-isobutyl-1-methylxanthine and dexamethasone stimulates cell-associated and soluble chondroitin 4-sulfate proteoglycans.

The proteoglycans (cell-associated and culture media) in 3T3-L1 preadipocytes in culture were analyzed before and during differentiation into adipocytes. Cells were metabolically labeled with [35S]sulfate and [3H] glucosamine for 24 h and then extracted and analyzed. There was a 1.68 +/- 0.07-fold increase in the 35S in medium proteoglycan during differentiation, whereas cell-associated proteoglycan radioactivity showed no increase. Analyses of radiolabeled molecules using ion-exchange chromatography, gel filtration, and high performance liquid chromatography after enzymatic or alkaline digestion indicated that all of the 35S label was recovered as two major species of chondroitin 4-sulfate proteoglycans (CSPG-I and CSPG-II) and 7% as heparan sulfate proteoglycan. CSPG-I has a mass of approximately 970 kDa with multiple chondroitin sulfate chains (average of 50 kDa each) and a core protein of approximately 370 kDa including oligosaccharides. CSPG-II has a mass of 140 kDa with one or two chondroitin sulfate chains (average of 68 kDa each) and a core protein of 41 kDa including oligosaccharides. CSPG-I appears to be similar to versican, whereas CSPG-II is similar to decorin and/or biglycan, found in other fibroblastic cells. Cell differentiation was associated with a specific increase in CSPG-I (4.0 +/- 0.2-fold in media and 3.2 +/- 0.5-fold in the cell-associated form). This system should facilitate study of the functional roles of proteoglycans during growth and differentiation.

1-Methyl-3-isobutylxanthine↗
PubMed1990

Developmental changes in testicular interstitial cell populations, LH receptors and in the response to hCG in the rat.

High doses of hCG were administered to immature rats of different ages and the animals killed 48 h later. Serum testosterone increased 2 to 4-fold over control values 48 h after hCG. In-vitro androgen production showed different patterns according to age. Animals younger than 35 days, when treated with hCG, retained the ability to respond to in-vitro gonadotrophic stimulation. This ability was lost in testes from rats aged 45 days. The number of free LH-receptors 48 h after hCG diminished with increasing age to become non-detectable at 35 and 45 days. In control animals the proportion of differentiated Leydig cells in relation to their mesenchymal precursors increased progressively with age to reach highest values at 45 days. hCG administration induced a shift of the cellular composition of the interstitium toward the more mature cell types. hCG has a predominantly trophic action on mesenchymal precursors in young rats, promoting their differentiation. These effects are minimal in the differentiated Leydig cells in older animals. It is proposed that the observed biochemical responses are the result of the balance between the increase in LH receptors and steroidogenic enzymes in the developing new generation of young Leydig cells and the down-regulation of receptors and enzymatic lesions in fully differentiated Leydig cells.

Aging↗
PubMed1988

Prolactin differentially affects bacterial toxin-induced ADP-ribosylation of Nb2 lymphoma cell membrane proteins.

Exposure of lactogen-dependent Nb2 lymphoma cells to prolactin for up to 72 hr caused time- and dose-dependent changes in the ability of specific 38 kDa and 41.5 kDa membrane proteins from these cells to be subsequently ADP-ribosylated by pertussis and cholera toxins, respectively. Whereas the sensitivity of the 41.5 kDa substrate to cholera toxin was already reduced after 1 hour, that of the 38 kDa substrate for cholera toxin was increased for up to 72 hours. These findings suggest that membrane G-proteins may mediate the effects of prolactin binding to its receptor, leading to the proliferation of Nb2 lymphoma cells.

Adenosine Diphosphate Ribose↗
PubMed1987

DNA topoisomerase I from Leydig cells is modulated by luteinizing hormone and cyclic adenosine monophosphate.

The action of luteinizing hormone on topoisomerase I activity from rat Leydig cells was studied. Stimulation of the enzyme was observed after long-term (24 and 48 h) gonadotrophin treatment in in vivo experiments. No change could be detected for shorter times than 12 h using two different experimental approaches. Topoisomerase I was stimulated by cAMP in a whole cell extract in a phosphorylation-dependent manner. These results suggest that topoisomerase I could be a target for nuclear events induced by peptide hormone action.

Animals↗
PubMed1987

Possible interaction of the adrenal-gonadal systems on brain catecholamines of adult male rats.

Studies from this laboratory showed that gonadectomy (GDX) alters biogenic amines concentrations in diencephalon during the first 40 days. While the GDX females maintain the differences at day 60, the differences are eliminated in males at that time. In the present work, we have studied in three cerebral regions the adrenal involvement in the mechanism responsible for this normalization of catecholamine concentration in long-term castrated adult male rats. A hypersecretion of adrenal steroids seems to compensate for the lack of gonadal effect when the orchidectomized rats reach adulthood only for diencephalic dopamine.

Adrenal Glands↗
PubMed1987

Acute hCG administration induces seminiferous tubule damage in the adult rat.

In order to study the early (or short time) effects of an hCG stimulation on the seminiferous tubules of the adult rat, a single dose of 100, 200 or 400 IU hCG was administered to eighty to ninety day old rats of the Sherman strain. The histological analysis revealed a tubular damage already noticeable six hours after the injection. This precocious lesion becomes more pronounced two to five days later, consisting of degeneration and hypocellularity of the germinal epithelium, margination of the chromatin in round spermatids and formation of multinuclear giant cells. This damage involves big areas of the testis, particularly of peripheral location. The analysis performed three months after the acute stimulation still showed tubular regressive changes, thus indicating an incomplete reversion of the damage. Changes in the hormonal environment of hCG treated rats were found. Serum testosterone significantly increased from 6 to 72 hours following a 200 IU hCG injection. A severe diminution of serum FSH levels and a significant increase of the serum estradiol were observed. Intratesticular administration of estradiol benzoate was able to reproduce the tubular damage in some animals, while restoration of FSH circulating levels by simultaneous administration of hCG and purified hFSH did not prevent the changes induced by hCG alone. These results suggest that the high intratesticular level of estradiol and not the lowering of serum FSH might be the mechanism responsible for the described testicular injury.

Animals↗
PubMed1986

Photoperiod, follicle-stimulating hormone receptors, and testicular function in vizcacha (Lagostomus maximus maximus).

In the present work we investigated the presence of testosterone in serum and follicle-stimulating hormone (FSH) receptors in testes of the vizcacha (Lagostomus maximus maximus), a South American rodent. We also investigated the effect of constant light on both parameters. The control group consisted of vizcachas caught in their natural habitat and maintained under continuous darkness; the experimental group consisted of animals maintained under constant light (1076 lx) for 8 days. The results revealed a significant decrease in serum testosterone and FSH receptors when the animals were maintained under constant light, as compared to the control group. Androstenedione was elevated in the serum obtained from the experimental group. It is postulated that the pineal gland may regulate testosterone secretion through FSH receptors and through an enzymatic blockade in the steroidogenic pathway; this supposition, however, remains to be proved.

Androstenedione↗
PubMed1985

Effects of radioiodination on hormone binding ability.

This paper presents the effects of 125I labelling on human chorionic gonadotropin binding ability. The results obtained showed a marked difference in the half-life of the specific radioactivity of the radiolabelled hormone comparing the one obtained by "self-displacement" analysis and that calculated considering the half-life of the radioactive isotope (60 days for 125I). The decrease in the hormone half-life (t 1/2 = 3.10 days) was demonstrated by binding experiments performed at various days after hormone labelling. The affinity constant (Ka) and the number of binding sites obtained after Scatchard analysis using rat testes as receptor source, remained constant when the "self-displacement" specific radioactivity was used while they varied significantly if the 60 days half-life was considered for the data processing. The importance of the labelled hormone degradation as a possible cause of the decrease in the binding ability is also described.

Animals↗
PubMed1984

Hypothalamic-hypophyseal-gonadal axis in the streptozotocin-induced diabetic male rat.

In the present work it was observed that the diabetic state alters the hypophyseal response to castration, without the expected increase in the LH serum levels, as found in the control rats. On the other hand, the stimulation of the hypophysis with LHRH resulted in a lower response in the case of the diabetic animal. The results presented herein are in good agreement with the finding of a reduction in the number of androgen binding sites and also with a diminished activity of the 5 alpha-reductase in the hypophysis from diabetic animals. The present results indicate an alteration in the hypophyseal gonadotropin production as well as in the overall process of hypophyseal response in experimental diabetes.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1984

Effect of a second injection of human chorionic gonadotropin on the desensitized Leydig cells.

Experimental evidence has demonstrated that multiple doses of LH will increase the steroidogenic capacity of Leydig cells. This work was undertaken with the aim of defining the effect of a second hCG administration on the desensitized state, measuring binding of the gonadotropin and the steroidogenic capacity of rat testes. A single injection of 200 IU hCG induced a sharp increase of plasma testosterone which was still evident 24 h later. A second peak was observed at 72 h. The in vivo refractoriness of Leydig cells between 24 and 72 h after the single injection was proved by the fact that a second administration of hCG, 2 h before sacrifice, did not induce any increase in plasma testosterone. A second administration of 200 IU hCG, 48 h after the first injection, showed a similar pattern but on the 5th day there was an increased stimulation of testosterone production with respect to that obtained after a single dose of hCG. The in vitro studies on testicular binding capacity and steroidogenic responsiveness showed that the second administration of hCG, 48 h after the first injection, maintained the testicular binding capacity at the lowest level and the 'adenylate cyclase desensitization' but restored the steroidogenic capacity to even supramaximal values, compared to normal rats, 3 days after this second hCG administration. These results would support a dissociation between receptor loss and maximal testosterone synthesis as well as possibly indicating an alternative pathway different from the classical.

Animals↗
PubMed1984

A simple computer program for Scatchard plot analysis of hormone receptors including statistical analysis on a low cost desk top calculator.

A simple procedure for the estimations of standard errors in hormone binding parameters derived from Scatchard analysis is proposed by assuming an univariate linear regression statistic model. The complete set of necessary formulae is presented and a practical way for calculation is solved using the binding of human growth hormone to rat adrenal membranes, as a practical example. The comparison between the results obtained by the method proposed and by using a well proved and accepted computer program, shows unequivocally that the differences are practically undistinguishable. The complete program to calculate the Scatchard parameters and their statistical analysis is available on request.

Binding Sites↗
PubMed1983

Measurement of specific radioactivities in labelled hormones by self-displacement analysis.

A graphical method is described that allows the determination of specific radioactivities of radioactively labelled hormones. This method combines the self-displacement technique, plotting bound/free ratios versus mass of unlabelled hormone or total radioactivity of labelled preparation added to the receptor preparation, and the maximal binding capacity of the labelled hormone. The procedure presented herein provides a more realistic specific radioactivity for use in all binding experiments. Application of the method is demonstrated for 125I-labelled ovine prolactin, and data are presented for 125I-labelled human choriogonadotropin and [3H]testosterone.

Animals↗
PubMed1983

Mitochondrial biosynthesis of cholesterol in Leydig cells from rat testis.

The subcellular location of some enzymes responsible for cholesterol biosynthesis was studied in metrizamide-purified rat Leydig cells. The highest activity of 3-hydroxy-3-methyl glutaryl coenzyme A reductase (HMG-CoA reductase), a key regulatory enzyme in the cholesterol pathway, was associated with highly enriched mitochondrial fractions with recovery of 62% of the total activity and was located on the inner membrane. A significant part of the activity (35%) was also present in the cytoplasm. The activity of this enzyme in the other subcellular fractions was negligible. The HMG-CoA synthase activity was also found almost entirely in the mitochondria (90%). Otherwise no detectable activity of HMG-CoA lyase was present in the subcellular fractions studied. Furthermore, cholesterol may be synthesized from acetyl-CoA inside the mitochondrion, since a significant incorporation (90%) of [14C]acetyl-CoA into digitonin-precipitable sterols was observed in this organelle and only 10% in the cytoplasmic fraction. The evidence strongly suggests that much of the cholesterol biosynthesis that takes place in Leydig cells is carried out within the mitochondria.

Acetates↗
PubMed1981

Effect of testosterone on the hypothalamic-pituitary-testicular axis of the old male rat.

Old rats show lower serum testosterone, a lower increase in serum LH either after orchidectomy or after LHRH stimulation, and a lower number of hCG binding sites in testis, compared to younger controls. Treatment with testosterone for 5 to 6 weeks was followed by an increment in the androgen serum levels of about 70% in adult, and of 170% in old animals, a reduction to about one half testicular weight in both groups, and an inhibition of similar magnitudes in the LH increase that followed castration or LHRH stimulation. Testosterone treatment reduced the binding sites for hCG in testis of young rats but did not correct the already low values observed in the old animals. It is suggested that similarities and differences occur in the hypothalamic-pituitary-testicular axis of young and old animals and that differences could be due to changes in set points regulation of the system and/or some intrinsic modification of the hormone producing mechanisms.

Animals↗