No abstract

The mechanism by which glucocorticoids induce various cellular responses in different tissues is only partially understood. Here we demonstrate that glucocorticoids stabilize the actin cytoskeleton of several cell types, as revealed by increased resistance of actin filaments to the disrupting effect of cytochalasin and by visible thickening of actin filament bundles. These effects require several hours to develop, require protein synthesis, and are accompanied by increased expression of the actin-binding protein caldesmon. These data may help to explain why glucocorticoids inhibit corticotropin release from pituitary cells, if interpreted in terms of the current idea that an actin filament "barrier" modulates exocytotic secretion in various cell types. In support of this idea, we find that in "model" corticotrophs (AtT-20 cells), glucocorticoids stabilize actin filaments and inhibit corticotropin release with similar potencies. Furthermore, we show here that glucocorticoid inhibition is overcome by exposing AtT-20 cells to concentrations of cytochalasin B or D that disrupt their stabilized actin filaments. On the other hand, our freeze-etch electron microscopy of AtT-20 cells has shown that actin rilaments do not, in fact, create a dense submembranous barrier that might prevent corticotropin secretory droplets from discharging; instead, they form open networks near the membrane that appear to hold secretory droplets in their interstices. We propose that the delicate physical crosslinks maintaining this actin-mediated membrane "docking" of secretory droplets may need to disconnect in order to permit corticotropin discharge and that these crosslinks may be stabilized along with the actin filaments in dexamethasonetreated cells.Glucocorticoids act by transcriptionally activating certain sets of genes in susceptible cells, but the subsequent steps that link this altered gene expression to the various cellular changes induced by glucocorticoids are generally unknown (1). In this report, we analyze the inhibitory effect of glucocorticoids on corticotropin (ACTH) release from pituitary cells. Studies of primary pituitary cultures and of pituitary tumor cells have shown that glucocorticoid-induced inhibition of ACTH secretion has two phases, one appearing in a few hours and the other requiring days of exposure to steroids. The latter, long-term effect is known to involve a decrease in ACTH synthesis, but the former, rapid-onset suppression of exocytotic release of hormone is less well understood (2, 3). Primary pituitary cell cultures are unsuitable for studying this effect because corticotrophs comprise only 2-5% of the total cell population, so we used instead a clonal cell line derived from a mouse tumor, which is well characterized and maintains several differentiated characteristics (4). As in normal corticotrophs, corticotropin-releasing factor (CRF) stimulates ACTH release from AtT-20 cells (4), and it does so by raising cAMP levels, leading to protein kinase A-mediated opening of voltage-dependent calci...

Objective: The Working Group on Uric Acid and Cardiovascular Risk of the Italian Society of Hypertension conceived and designed an ad-hoc study aimed at searching for prognostic cut-off values of serum uric acid (SUA) in predicting fatal myocardial infaction (MI) in women and men. Methods: The URic acid Right for heArt Health study is a nationwide, multicentre, observational cohort study involving data on individuals aged 18–95 years recruited on a regional community basis from all the territory of Italy under the patronage of the Italian Society of Hypertension with a mean follow-up period of 122.3 ± 66.9 months. Results: A total of 23 467 individuals were included in the analysis. Cut-off values of SUA able to discriminate MI status were identified by mean of receiver operating characteristic curves in the whole database (>5.70 mg/dl), in women (>5.26 mg/dl) and in men (>5.49 mg/dl). Multivariate Cox regression analyses adjusted for confounders (age, arterial hypertension, diabetes, chronic kidney disease, smoking habit, ethanol intake, BMI, haematocrit, LDL cholesterol and use of diuretics) identified an independent association between SUA and fatal MI in the whole database (hazard ratio 1.381, 95% confidence intervals, 1.096–1.758, P = 0.006) and in women (hazard ratio 1.514, confidence intervals 1.105–2.075, P < 0.01), but not in men. Conclusion: The results of the current study confirm that SUA is an independent risk factor for fatal MI after adjusting for potential confounding variables, and demonstrate that a prognostic cut-off value associated to fatal MI can be identified at least in women.

Objective: Although the relationship between hyperuricemia and cardiovascular events has been extensively examined, data on the role of diuretic-related hyperuricemia are still scanty. The present study was designed to collect information on the relationship between diuretic-related hyperuricemia and cardiovascular events. Methods: The URic acid Right for heArt Health (URRAH) study is a nationwide, multicentre, observational cohort study involving data on individuals recruited from all the Italy territory under the patronage of the Italian Society of Hypertension with an average follow-up period of 122.3 ± 66.9 months. Patients were classified into four groups according to the diuretic use (yes vs. no) and serum uric acid (SUA) levels (higher vs. lower than the median value of 4.8 mg/dl). All-cause death, cardiovascular deaths and first cardiovascular event were considered as outcomes. Results: Seventeen thousand, seven hundred and forty-seven individuals were included in the analysis. Mean age was 57.1 ± 15.2 years, men were 45.3% and SBP and DBP amounted to 144.1 ± 24.6 and 85.2 ± 13.2 mmHg. 17.2% of individuals take diuretics of whom 58% had SUA higher than median value. Patients with hyperuricemia without diuretic use served as reference group. In multivariate adjusted analysis (sex, age, SBP, BMI, glucose, total cholesterol, and glomerular filtration rate) individuals with hyperuricemia and diuretic use exhibit a similar risk for the three outcomes as compared with the reference group. Conclusion: Our study showed that diuretic-related hyperuricemia carry a similar risk of cardiovascular events and all-cause mortality when compared with individuals that present hyperuricemia in absence of diuretic therapy.

Abstract. Calciosomes are small cytoplasmic vacuoles identified in various nonmuscle cell types by their content of protein(s) similar to calsequestrin (CS), the Ca 2+ storage protein of the muscle sarcoplasmic reticulum (SR). These entities have been interpreted as the "primitive" counterpart of the SR, and suggested to be the organelle target of inositol-l,4,5-triphosphate action (Volpe, P., K. H. Krause, S. Hashimoto, E Zorzato, T. Pozzan, J. Meldolesi, and D. P. Lew. Proc. Natl. Acad. Sci. USA. 85:1091-1095). Immunoperoxidase and immunogold experiments carried out in both thick and ultrathin cryosections of rat hepatocytes and pancreatic acinar cells by using antimuscle CS antibodies revealed a specific labeling widely distributed in the entire cytoplasm, while nuclei were negative. Individual calciosomes appeared as small (105 nm) membrane-bound vacuoles intermingled with, and often apposed to ER cisternae and mitochondria. Other calciosomes were scattered in the Golgi area, in between zymogen granules and beneath the plasma membrane. The cumulative volume of the CS-positive organelles was measured to account for the 0.8 and 0.45 % of the cytoplasm in liver and pancreas cells, respectively. The real total volume of the calciosome compartment is expected to be approximately twice as large. In hepatocytes, structures similar to CS-positive calciosomes were decorated by antibodies against the Ca 2÷ ATPase of muscle SR, while ER cisternae were not. By dual labeling, colocalization was revealed in 53.6% of the organelles, with 37.6% positive for the ATPase only. CS appeared preferentially confined to the content, and the Ca 2÷ ATPase to the contour of the organelle. The results suggested a partial segregation of the two antigens, reminiscent of their well-known segregation in muscle SR. Additional dual-label experiments demonstrated that hepatic calciosomes express neither two ER markers (cytochrome-P450 and NADH-cytochrome b5 reductase) nor the endolysosome marker, luminal acidity (revealed by 3-[2,4-dinitroanilino]-3'-amino-N-methyl dipropylamine). Calciosomes appear as unique cytological entities, ideally equipped to play a role in the rapid-scale control of the cytosolic-free Ca 2÷ in nonmuscle cells. CYTOPLASMIC Ca 2+ storage organelles capable of both high affinity uptake and rapid triggered release of Ca 2÷ are believed to be ubiquitous among eukaryotic cells (3, 9). So far, however, the intracellular structure responsible for these activities has been identified with certainty only in striated muscle fibers, where a specific, highly developed tubular network, the sarcoplasmic reticulum (SR) ~, accounts for the [Ca2+]i fluctuations that underly the contraction-relaxation cycle. The SR is endowed with two major proteins: a Ca 2+ ATPase, which accounts for over 80% of its membrane proteins, and is responsible for the high affinity Ca 2+ uptake; and calsequestrin (CS), a high ca-1. Abbreviations used in this paper: Ab(s), antibody(ies); CS, calsequestrin; DAMP, 3-(2,4-dinitroanilino)-3'-amino-N-methyl-diprop...