The regulation of thyroid function during normal pregnancy: importance of the iodine nutrition status

The main change in thyroid function associated with the pregnant state is the requirement of an increased production of thyroid hormone that depends directly upon the adequate availability of dietary iodine and integrity of the glandular machinery. Physiologic adaptation takes place when the iodine intake is adequate, while this is replaced by pathologic alterations when there is a deficient iodine intake. Pregnancy acts typically, therefore, as a revelator of underlying iodine restriction. Iodine deficiency (ID) has important repercussions for both the mother and the fetus, leading to sustained glandular stimulation, hypothyroxinemia and goitrogenesis. Furthermore, because severe ID may be associated with an impairment in the psycho-neuro-intellectual outcome in the progeny-because both mother and offspring are exposed to ID during gestation (and the postnatal period), and because ID is still prevalent today in several European countries-it has been proposed already in the early 1990s that iodine supplements be given systematically to pregnant and breast-feeding women. Particular attention is required to ensure that pregnant women receive an adequate iodine supply, by administering multivitamin tablets containing iodine supplements, in order to achieve the ideal recommended dietary allowance of 200-250 microg iodine/day.     

The importance of calcium ions for the regulation of guanosine 3':5'-cyclic monophosphage levels

Guanosine 3':5'-cyclic monosphosphate (cyclic GMP) levels in the ductus deferens of the rat were increased 2- to 3-fold by acetylcholine (10-1000 muM) or by 125 mM KCl, while adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels were not changed. After incubation for 30 min in the absence of Ca(++), cyclic GMP control levels were decreased by 85% and were not affected by acetylcholine or KCl. The readdition of Ca(++) (1.8 mM) for 3 min to Ca(++)-deprived tissue partially restored basal cyclic GMP levels and the effects of acetylcholine and KCl. The addition of Sr(++) (3.6 mM) or of Ba(++) (1.8 or 10 mM) also caused an increase in basal cyclic GMP in Ca(++)-deprived tissue. Cyclic AMP levels were not significantly changed under any of these conditions. The addition of the phosphodiesterase inhibitor, 1-methyl-3-isobutylxanthine (0.1 mM), to ductus deferentes increased the amount of cyclic AMP about 50% and that of cyclic GMP about 2-fold. The later effect also depended on the presence of Ca(++). 1-Methyl-3-isobutylxanthine (0.1 mM) increased cyclic GMP and cyclic AMP levels in slices of rat submaxillary glands. Methacholine increased cyclic GMP if added in the presence of methyl isobutylxanthine. Cyclic GMP control levels and the effect of methyl isobutylxanthine were unchanged by Ca(++) omission, but the effect of methacholine was abolished.These findings indicate that calcium ions are important for the control of cyclic GMP levels in these tissues.     

The role of extracellular matrix stiffness in megakaryocyte and platelet development and function

The extracellular matrix (ECM) is a key acellular structure in constant remodeling to provide tissue cohesion and rigidity. Deregulation of the balance between matrix deposition, degradation, and crosslinking results in fibrosis. Bone marrow fibrosis (BMF) is associated with several malignant and nonmalignant pathologies severely affecting blood cell production. BMF results from abnormal deposition of collagen fibers and enhanced lysyl oxidase‐mediated ECM crosslinking within the marrow, thereby increasing marrow stiffness. Bone marrow stiffness has been recently recognized as an important regulator of blood cell development, notably by modifying the fate and differentiation process of hematopoietic or mesenchymal stem cells. This review surveys the different components of the ECM and their influence on stem cell development, with a focus on the impact of the ECM composition and stiffness on the megakaryocytic lineage in health and disease. Megakaryocyte maturation and the biogenesis of their progeny, the platelets, are thought to respond to environmental mechanical forces through a number of mechanosensors, including integrins and mechanosensitive ion channels, reviewed here.     

The importance of autophagy regulation in obstructive sleep apnea

Purpose

Autophagy, the self-renewal process of cells, is dependent on lysosomes to degrade damaged organelles and proteins. The increased or damaged level of autophagy is proven to relate to a number of disorders, including metabolic disorders, malignant tumors, pulmonary diseases, and neurodegenerative disorders. This review aims to examine the effects of autophagy on the pathogenic mechanism of obstructive sleep apnea (OSA) in order to guide relevant disease treatment.

Methods

We conducted a search of the literature using the electronic database, focusing on articles that explored the association between OSA and autophagy.

Conclusion

OSA can induced autophagy through hypoxia, oxidative stress, endoplasmic reticulum stress, endothelial dysfunction, miRNA, etc. We propose that the mechanism of the autophagy in patients with OSA should be eclucidated in further studies.

     

The importance of measuring ionized calcium in characterizing calcium status and diagnosing primary hyperparathyroidism

Context: Serum total calcium (tCa) is routinely measured for diagnosing calcium disorders but may not reflect levels of biologically active ionized calcium (iCa) in disease or detect all cases of primary hyperparathyroidism. Objective: We investigated the utility of measuring iCa and tCa for diagnosing primary hyperparathyroidism. Design: This was an observational, retrospective, cross-sectional study. Patients: We studied a biochemistry cohort of consecutive ambulatory outpatients with suspected bone or calcium metabolism disorders referred for calcium metabolism biochemistry panels and a surgical cohort of consecutive tertiary hospital patients whose parathyroid specimens were submitted to a single center, and consecutive parathyroidectomy patients of a single surgeon with specimens submitted to a different center. Results: In 5490 biochemistry cohort patients, discordance between iCa and tCa in classifying calcium status occurred in 12.6% of cases overall but was worse in hypercalcemic (whether defined by tCa and/or iCa) cases (49%) and hypocalcemic cases (92%). Reliance on tCa alone would miss 45% with ionized hypercalcemia. In 315 biochemistry cohort cases with PTH-dependent hypercalcemia, 130 (41%) had isolated ionized hypercalcemia at diagnosis. In 143 patients with histologically proven parathyroid disease, 24% had isolated ionized hypercalcemia at diagnosis. These patients were younger (P = 0.022) with milder ionized hypercalcemia and better renal function (both P ≤ 0.001) than patients presenting with concurrently elevated iCa and tCa. Conclusion: In abnormal calcium states, tCa frequently disagrees with iCa in classifying calcium status. Histologically proven parathyroid disease can present with isolated ionized hypercalcemia. Measurement of iCa is required to accurately assess calcium status and improve diagnostic accuracy.     

Ion channel regulation of intracellular calcium and airway smooth muscle function

Airway hyper-responsiveness associated with asthma is mediated by airway smooth muscle cells (SMCs) and has a complicated etiology involving increases in cell contraction and proliferation and the secretion of inflammatory mediators. Although these pathological changes are diverse, a common feature associated with their regulation is a change in intracellular Ca²⁺ concentration ([Ca²⁺]_i). Because the [Ca²⁺]_i itself is a function of the activity and expression of a variety of ion channels, in both the plasma membrane and sarcoplasmic reticulum of the SMC, the modification of this ion channel activity may predispose airway SMCs to hyper-responsiveness. Our objective is to review how ion channels determine the [Ca²⁺]_i and influence the function of airway SMCs and emphasize the potential of ion channels as sites for therapeutic approaches to asthma.     

Extracellular matrix structure and nano-mechanics determine megakaryocyte function

Cell interactions with matrices via specific receptors control many functions, with chemistry, physics, and membrane elasticity as fundamental elements of the processes involved. Little is known about how biochemical and biophysical processes integrate to generate force and, ultimately, to regulate hemopoiesis into the bone marrow-matrix environment. To address this hypothesis, in this work we focus on the regulation of MK development by type I collagen. By atomic force microscopy analysis, we demonstrate that the tensile strength of fibrils in type I collagen structure is a fundamental requirement to regulate cytoskeleton contractility of human MKs through the activation of integrin-α2β1-dependent Rho-ROCK pathway and MLC-2 phosphorylation. Most importantly, this mechanism seemed to mediate MK migration, fibronectin assembly, and platelet formation. On the contrary, a decrease in mechanical tension caused by N-acetylation of lysine side chains in type I collagen completely reverted these processes by preventing fibrillogenesis.     

The significance of megakaryocyte size

Normal guinea pig and human megakaryocytes in suspension were measured with an optical micrometer. The range of megakaryocyte diameters in both species was from 10 to about 65 micrometer. Approximately 20%-25% of megakaryocytes were smaLler than 20 micrometer in diameter and were mostly missed in past studies. However, virtually the entire population of megakaryocytes was larger than all but a very small percent of the other marrow cells. This size range and the existence of a visual threshold size between the megakaryocytes and nonmegakaryocytes were confirmed by flow cytometric analysis of fresh unfixed cells. On human bone marrow smears there was some flattening of all cell types, but the megakaryocytes were consistently at least minimally greater in size than almost all the nonmegakaryocytes. Normal marrow cells greater than 20 micrometer in diameter were always megakaryocytes. Cells 14-20 micrometer were still noticeably larger than the general marrow population; thus easily found, they could be examined for specific morphological criteria. Size, therefore, is a useful first criterion for the identification of megakaryocytes. The larger sizes of megakaryocytes were related to their greater DNA content per cell (polyploidy) compared to nonmegakaryocytes. The relationship between megakaryocyte size, ploidy, and maturation was examined by the simultaneous measurement for the first time of each of these parameters in the same cell. Maturation was quantitated by the new scheme based on the progressive changes in megakaryocytes nuclear configuration. Within each maturation stage the mean cell volume of guinea pig megakaryocytes doubled with each ploidy doubling. Within each ploidy group, the sizes of megakaryocytes increased with maturation stage. However, maturation and polyploidization appear to be linked; the data showed that 80% of the low ploidy (4N-8N) megakaryocytes were immature and that 95% of the platelet-shedding megakaryocytes were 16N-32N.     

The effects of low-dose vincristine on megakaryocyte colony-forming cells and megakaryocyte ploidy

S ummary. The administration of low-dose vincristine (VCR) (0.1 mg/kg) to mice resulted in thrombocytosis without prior thrombocytopenia. No significant changes in marrow megakaryocyte numbers were found. However, after a minor early decrease, mean megakaryocyte ploidy increased, with a peak at 3 d. The number of megakaryocyte colony-forming cells (MEG-CFC) in bone marrow did not change significantly. In contrast with the effects on marrow, the concentration of megakaryocytes and the content of MEG-CFC in the spleen were significantly reduced for 1–2 d after VCR. This reduction was followed by a compensatory rise in the splenic content of MEG-CFC (peak 3-fold increase at 3 d), and 1–2 d later, an increase in splenic megakaryocytes which was concurrent with the increased platelet count. Culture of marrow and spleen cells in the presence of VCR resulted in inhibition of megakaryocyte colony formation at concentrations > 5 ng/ml and parallel reduction of the number of megakaryocytes per colony and the mean ploidy of colony megakaryocytes.
The results suggest that the thrombocytosis induced by low-dose VCR does not result simply from an effect on platelets, but reflects compensatory changes in megakaryopoiesis secondary to toxic suppression of megakaryocytes and their progenitors.     

The release of calcium from cardiac mitochondria: The importance of the calcium-protein ratio

Summary Using a DW 2 dual wavelength spectrophotometer (AMINCO) and murexide as a Ca²⁺ sensitive indicator it is shown that guinea-pig heart mitochondria can release accumulated Ca²⁺ without the influence of non-physiological material. The main factor which decides if accumulated Ca²⁺ is spontaneously released is the Ca²⁺/mitochondrial-protein ratio. Under appropriate assay conditions a critical intramitochondrial Ca²⁺ concentration is reached. Increasing this concentration leads to Ca²⁺-release.

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Kalzium-Freisetzung aus Herzmitochondrien: Das Kalzium-Mitochondrienprotein-Verhältnis als entscheidendes Kriterium

Zusammenfassung Mit Hilfe eines Doppelwellenlängen-Photometers (DW-2, AMINCO) und von Murexid als Ca²⁺-Indikator konnte gezeigt werden, daß Meerschweinchen-Herz-mitochondrien auch ohne den Zusatz unphysiologischer Agenzien (wie Entkopplern oder Ruthenium Rot) gespeichertes Calcium spontan wieder freisetzen können. Entscheidend für diese spontane Ca²⁺-Freisetzung ist das Verhältnis von Calcium und Mitochondrienprotein. Unter bestimmten definierten Bedingungen stellt sich eine kritische intramitochondriale Ca²⁺-Konzentration ein; wird dieser Schwellenwert überschritten, tritt spontane Ca²⁺-Freisetzung ein.

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With 2 figures and 1 table

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Supported by the Deutsche Forschungsgemeinschaft-SFB 89-Kardiologie, Göttingen, the British Heart Foundation and the Medical Research Council of Great Britain.     

Prolonged thrombocytosis in mice after 5-fluorouracil results from failure to down-regulate megakaryocyte concentration. An experimental model that dissociates regulation of megakaryocyte size and DNA content from megakaryocyte concentration

Rodents treated with 150 mg/kg of 5-fluorouracil (5-FU) exhibit a marked and prolonged rebound thrombocytosis, suggesting that feedback control of one or more megakaryocyte characteristics (size, polyploidy, or concentration) is altered. To determine the changes in megakaryocytes that lead to such a profound thrombocytosis, C3H mice were injected with 150 mg/kg 5-FU, and platelet and megakaryocyte responses were examined at frequent intervals from days 1 through 25. After 5-FU injection, all megakaryocyte indices decreased, as did platelet number. However, the decrease in platelets to one third of control was greater than the decreases in megakaryocyte indices, suggesting that thrombocytopoiesis was ineffective from days 3 through 7 post 5-FU. Megakaryocyte size began to recover on day 4, followed by polyploid DNA content on day 5, and megakaryocyte concentration and platelets at 7.5 days. Megakaryocyte size peaked on days 6 through 8 (1.25 x normal), followed by megakaryocyte polyploid DNA content on day 8, megakaryocyte concentration on days 9 through 12 (2 1/2 to 3x normal), and platelets on days 12 through 15 (2x normal). Platelet levels are thought to be important in the feedback regulation of megakaryocytes; however, only polyploid DNA content distributions showed a close inverse relationship to platelet counts during both the recovery and rebound thrombocytosis phases after 5-FU. In contrast, megakaryocyte size peaked before platelet recovery commenced, while megakaryocyte concentration increased in parallel with platelets from 7.5 to 10 days post 5-FU and continued to be maintained at 2 to 3 times normal through day 13, despite platelet levels that were more than twice normal. Both megakaryocyte size and polyploid DNA content distributions shifted toward lower values in response to the rebound thrombocytosis (DNA content on day 10 and size on days 12 and 13). Splenectomy did not substantially alter the pattern of post 5-FU rebound thrombocytosis or megakaryocyte response from that seen in intact mice, indicating that splenic megakaryocytes are not responsible for the prolonged thrombocytosis seen after this drug. In summary, the prolonged thrombocytosis after 5-FU administration results from failure to down-regulate the number of precursors entering the differentiating megakaryocyte compartment. These data indicate that megakaryocyte size and DNA content are responsive to different feedback controls than megakaryocyte concentration in this model system.     

Cellular calcium regulation in hypertension

In vascular muscle cells, two distinct types of functionally important calcium (Ca2+) channels, called transient (T) and sustained (L), are differentiated by dihydropyridine calcium antagonists (CaA). We studied the ratio of T/L Ca2+ channels in isolated, spontaneously contracting azygous venous cells of spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) by quantitating Ca2+ currents and intracellular Ca2+ release. While total transmembranous Ca2+ current was not different between the two strains, the proportion of Ca2+ currents carried by L-type channels was enhanced in vascular muscle cells from SHR. We have recently compared subcellular distribution of intracellular free Ca2+ concentration in the same cells, at rest and during stimulation, by quantitation with a digital photon-counting camera. Fura-2 fluorescence intensity showed that Ca2+ release was principally from sarcoplasmic reticulum and that cells from SHR had higher levels of Ca2+ upon calcium channel stimulation, especially at the cell periphery. These findings suggest fundamental differences in SHR and WKY vascular muscle cells implicating the importance of changes in calcium channels, modulation of Ca2+ release, and Ca2+ uptake in SHR hypertension.     

Participation of voltage-dependent calcium channels in the regulation of adrenal glomerulosa function by angiotensin II and potassium

The stimulation of aldosterone secretion from adrenal glomerulosa cells by angiotensin II (AII), potassium, and ACTH is highly dependent on the extracellular calcium concentration. To evaluate the role of voltage-dependent calcium channels in aldosterone production, we analyzed the actions and binding of calcium channel antagonists in collagenase-dispersed adrenal glomerulosa cells and membrane-rich particles. In rat glomerulosa cells, nifedipine caused dose-dependent inhibition of the aldosterone responses to AII and potassium, with half-maximum inhibitory concentration (IC50) of 100 nM, but had no effect on ACTH or 8-bromo-cAMP stimulated steroidogenesis in adrenal glomerulosa and fasciculata cells. Binding studies with [3H]nitrendipine in adrenal glomerulosa cells revealed a high affinity site with dissociation constant (Kd) of 0.4 +/- 0.1 nM, similar to that described in other tissues but about 100-fold lower than the IC50 for blockade of aldosterone production. However, Scatchard analysis of binding data from three of seven experiments in isolated adrenal glomerulosa cells revealed a low affinity site with Kd of 130 nM, in agreement with the IC50 for the effect of nifedipine on aldosterone production. In rat adrenal particles, nitrendipine-binding sites were located in the adrenal capsule and medulla and were undetectable in the zona fasciculata. Furthermore, there was a close correlation (r = 0.92) between the concentrations of nitrendipine-binding sites and AII receptors in the different zones of the adrenal in rat, dog, and cow, suggesting a functional relationship between AII receptors and calcium channels. These studies have shown a major and selective role of voltage-dependent calcium channels in the control of aldosterone secretion by the major physiological regulators, AII and potassium.     

The role of calcium in the age-related decline of neutrophil function

Upon activation by formyl-methionyl-leucyl-phenylalanine (FMLP), either in the presence of absence of cytochalasin B, neutrophils from old subjects generated significantly less superoxide than did neutrophils from the young. This reduction in activity was associated with a significant decrease in the basal cytosolic calcium concentration and a diminished flux of calcium to the cytosol after activation. At all concentrations of FMLP tested, cytosolic calcium remained significantly lower in neutrophils from the old as compared with the young, whereas permeability to extracellular calcium and efflux of calcium from the cell were also significantly diminished. Pretreatment of the cell with the ionophore ionomycin elevated the cytosolic calcium concentration and significantly improved function in old neutrophils. These findings demonstrate that aging results in alterations in neutrophil calcium homeostasis that may play a role in the age-related decline in neutrophil function.