Biomedical subjects

J C Calvo

Publications and source records attributed to J C Calvo.

45 records · Page 3Linked to original sources

PubMed1981

Specific prolactin binding in the rat adrenal gland: its characterization and hormonal regulation.

Rat adrenal prolactin receptors possess the same hormonal specificity as those in the prostate gland and liver, but are less stable during storage and after freezing. There is a gradual decrease in specific prolactin binding to the adrenal during sexual maturation in male rats; maximum binding capacity of 980 fmol/mg protein is at 25 days of age decreasing to approximately 100 fmol/mg protein at day 90. Prolactin receptors in the prostate are high at 25 days of age (700 fmol/mg protein), decrease sharply by day 30 (180 fmol/mg protein) and then gradually increase. Ovariectomy resulted in a significant rise in total prolactin binding in the adrenal gland, while the administration of oestradiol or testosterone reduced the binding, the reverse of changes in prolactin binding in the liver. Only oestrogen increased serum levels of prolactin in female rats. Ovine prolactin (500 micrograms) given to female rats resulted in a rapid increase over a period of 2-8 h total prolactin receptors in the adrenal, and these then decreased to normal levels, indicating a possible positive regulation of prolactin receptors by homologous hormone.

Adrenal Glands↗

PubMed1980

Androgen receptors in the diabetic rat.

Male rats rendered diabetic by IV streptozotocin (65 mg/kg body weight) were treated with exogenous insulin or testosterone. Charcoal-coated dextran and polyacrylemide gel electrophoresis techniques were employed in studying the characteristics of androgen (R1881) binding to prostate cytosol protein. In comparison with normal (N) rats, the replacement therapy of diabetic (D) animals with insulin (D + I) or testosterone (D + T) was able to restore epididymal weight (N = 0.40 +/- 0.04 g; D = 0.18 +/0 0.02 g; D + I = 0.42 +/- 0.05 g; D + T = 0.40 +/0 0.06 g) and total prostate weight (N = 0.24 +/- 0.02 g; D = 0.15 +/- 0.02 g; D + I = 0.24 +/- 0.05 g; D + T = 0.35 +/- 0.06 h). Testicular endogenous content of testosterone was restored after insulin treatment (N = 154 +/- 13 ng/testis; D = 41 +/- 5 ng/testis; D + I = 142 +/- 9 ng/testis), and significant improvements of serum testosterone levels were also achieved (N = 540 +/- 64 ng/100 ml; D = 238 +/- 37 ng/100 ml; D + I = 358 +/- 18 ng/100 ml). Prostate cytosol of streptozotocin-diabetic rats had strongly lowered capacity for 3H-R1881 binding compared with controls (94 and 12 fmol/mg protein, respectively). Testosterone treatment produced a 3.3-fold improvement of this lowered value, whereas the increment seen with insulin was less (1.5-fold). It is emphasized that some of the improvements caused by insulin replacement therapy in diabetic animals are due to the partial restoration of testosterone secretion. Thus, the combined actions of insulin and testosterone (instead of insulin alone) seem to be of major importance in the maintenance and regulation of accessory sex glands function.

Animals↗

PubMed1979

NADPH generating enzymes in Leydig cells from diabetic rats.

Impaired testosterone biosynthesis in Leydig cells from streptozotocin treated rats is correlated with the reduced activity of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and isocitrate dehydrogenase. The results shown demonstrate that in the diabetic state the activity of these enzymes is reduced by almost 50 to 59% from normal levels. Insulin treatment restored their activities to normal levels. The diminished supply of NADPH in diabetic interstitial tissue is not the unique factor in the control of steroidogenesis, since the availability of large amounts of exogenous NADPH in the incubations of Leydig cell did not reduce the differences in testosterone synthesis observed when compared with normal cells.

Animals↗

PubMed1978

Insulin regulation of Leydig cell luteinizing hormone receptors.

The effect of experimentally induced diabetes on the luteinizing hormone-human chorionic gonadotropin receptors in rat testes was examined. Pancreatectomy and streptozotocin diabetes the gonadotropin receptors and the administration of insulin restored the binding capacity to normal values. No differences in the association constant as well as the sedimentation coefficients of the luteinizing hormone-human chorionic gonadotropin receptor complexes were observed between normal and diabetic animals.

Animals↗

PubMed1976

A simple method for measuring 125I by liquid scintillation counting.

Scintillation solutions containing surface active substances, soluble in Toluene, could be used for efficient counting of 125I. The use of Triton X-114 in the proportion 30% v/v with a Toluene-2,5-Diphenyloxazole basic scintillation solution, provides a method for the measurement of liquid and solid samples with 50% efficiency and aqueous sample capacity up to 25%.

Chorionic Gonadotropin↗

PubMedDate not supplied

Kinetic properties of microsomal 3beta hydroxysteroid dehydrogenase-isomerase from the testis of Bufo arenarum H.

3beta-hydroxysteroid dehydrogenase 5-ene isomerase (3betaHSD/I) activity is necessary for the biosynthesis of hormonally active steroids. A dual distribution of the enzyme was described in toad testes. The present study demonstrates that in testicular tissue of Bufo arenarum H., microsomal 3betaHSD/I has more affinity for dehydroepiandrosterone (DHEA) than for pregnenolone (K(m)=0.17+/-0. 03 and 1.02 microM, respectively). The Hill coefficient for the conversion of DHEA and pregnenolone were 1.04 and 1.01, respectively. The inclusion of DHEA in the kinetic analysis of pregnenolone conversion affected V(max) while K(m) was not modified, suggesting a non-competitive inhibition of the conversion of pregnenolone. K(i) was calculated from replot of Dixon's slope for each substrate concentration. K(i) from the intercept and the slope of this replot were similar (0.276+/-0.01 and 0.263+/-0.02 microM) and higher than the K(m) for DHEA. The K(m) and K(i) values suggest the presence of two different binding sites. When pregnenolone was present in the assays with DHEA as substrate, no effect was observed on the V(max) while K(m) values slightly increased with pregnenolone concentration. Consequently, pregnenolone inhibited the transformation of DHEA in a competitive fashion. These studies suggest that, in this species, the microsomal biosyntheses of androgens and progesterone are catalysed by different active sites.

Animals↗

PubMedDate not supplied

Dose-dependence of the effects of corticosterone and the non-glucocorticoid, 18-hydroxycorticosterone, on the brush-border Na+/K+ exchanger.

Up to now, only glucocorticoids were thought to act on the renal proximal Na+/H+ exchanger. Using fluorimetric techniques we studied the kinetics of Na+/H+ exchange in brush border vesicles from ADX rats treated with increasing doses of corticosterone (B) and 18-hydroxycorticosterone (18OHB). Significant linear correlations were obtained when the Vmax of each treatment were plotted against log doses. 18OHB exhibits a slightly higher sensitivity than B and log-dose responses were steeper for 18OHB than for B treated rats. Differences between both treatments were highly significant at the 4.8 microg/100 g level, corresponding to the physiological blood level of 18OHB. Physiological doses of both steroids elicited equal Na+/H+ exchange-responses. 18OHB is not a glucocorticoid since even 88 microg/100 g did not promote hepatic glycogen deposition while the same dose of B increases glycogen deposits 3.5-fold. These results demonstrate the importance of the Na+/H+ exchanger as a mediator between corticoid action and H+ transport and that of the non-glucocorticoid 18OHB in this process.

18-Hydroxycorticosterone↗

PubMedDate not supplied

Heparin increases the adhesion of murine mammary adenocarcinoma cells (LM3). Correlation with the presence of heparin receptors on cell surface.

Mastocytosis is a common feature around solid tumors. Due to mast cell (MC) degranulation, heparin and other chemical mediators are released to surrounding tissues. The aim of this paper is to investigate the role of heparin and chemically modified heparins, on a murine mammary adenocarcinoma cell line adhesion properties, and the relationship with the presence of heparin binding sites in tumor cells. We show that heparin increases tumor cell adhesion in a dose-dependent manner. When the number of heparin binding sites was regulated, by culturing the cells with different FCS concentration for 24 hours, a correlation between binding capacity and heparin effect on cell adhesion was observed. The increment on cell adhesion by heparin was lower on cells with less heparin binding sites. Moreover, only heparin and a chemically modified heparin (partially N-desulfated N-acetylated), which bound to heparin-receptor, retained the ability to stimulate cell adhesion, while other modified heparins lost both effects. The increase in cell adhesion was observed on plastic dishes, albumin, as well as on fibronectin pre-coated ones suggesting that heparin effect is substratum independent. Our results show a direct relation between heparin binding to specific cell receptors and increase in cell attachment.

Adenocarcinoma↗

PubMedDate not supplied

Acute effects of two natural corticosteroids on the kinetics of the Na+/H+ exchanger in rat renal brush-border membranes.

We studied the effect of adrenalectomy and acute hormone replacement, using physiological doses of natural corticosteroids, on the kinetics of the Na+/H+ exchanger in brush border membrane vesicles. We collected the data using the acridine orange uptake technique. Adrenalectomized (ADX) rats presented a decreased maximal rate (Vmax) when compared with sham-operated animals (30,000 versus 41,000 fluorescent units/min, respectively). Administration of corticosterone (B) to ADX rats restored Vmax to values above control (up to 66,000 fluorescent units/min). Smaller doses of 18-OH-B led to similar results. K(m) (16 mM) remained the same for all the groups. Amiloride behaved as a pure competitive inhibitor, with a Ki = 0.02 mM and an I50 = 98 microM (in the presence of 50 mM sodium gluconate). The presence of sodium in the external buffer, before adding the vesicles, inhibited the exchange, with an I50 = 2 mM. We observed, a significant decrease in the Na+/H+ exchanger under non-acidotic conditions in response to adrenalectomy. Acute administration of physiological doses of natural occurring corticosteroids reversed the effect.

18-Hydroxycorticosterone↗