Inhibition of the proliferation of cultured immortalized schwann cells by forskolin with a decreased basal level of diacylglycerol

The repetitive passages of a Schwann cell culture results in the appearance of immortalized cells. In order to investigate the direct effects of cyclic AMP (cAMP) on Schwann cell proliferation, we used the immortalized Schwann cells because the responses of a short-term Schwann cell culture to agents increasing the intracellular cAMP are more complicated and it does not seem that all of them are due to the direct effects of cAMP. By adding up to 200 M of forskolin, an adenylate cyclase activator, to the culture medium, Schwann cell proliferation was inhibited and the intracellular 1,2-diacylglycerol (DG) level was decreased in a dose-dependent manner to 44 and 53% of the control values, respectively. The protein phosphorylation activity in the cytosol from the cell treated with 100 M forskolin, assayed with myelin basic protein as the acceptor, decreased to 78% and this inhibition was then reversed by the addition of 1-oleoyl-2-acetyl-sn-glycerol (OAG), a membrane-permeable DG, to the assay mixture. The cell proliferation inhibited by forskolin was also restored by the addition of OAG. These data suggest that cAMP inhibits both the activity of protein kinase C (PKC) and consequently cell proliferation through suppression of intracellular DG level, an activator of PKC. Since the inositol 1,4,5-triphosphate level and the hydrolysis of phosphatidylcholine to DG and phosphorylcholine were not affected, forskolin therefore appears to suppress the de novo synthesis of DG.     

Regional changes in muscle mass and strength following 20 days of bed rest, and the effects on orthostatic tolerance capacity in young subjects

To this day, many studies have suggested that prolonged bed rest (BR) affects on muscle mass and strength not only in gravity muscles but also in ungravity muscles. However, it is still unclear whether the decrease in regional muscle strength after BR is due to the alterations in the corresponding muscle mass, or not. On the other hand, if BR decreases the mass of antigravity muscles (UGM) as well as muscle strength and then increases tissue compliance of the antigravity muscles, orthostatic tolerance capacity will be decreased by the reduction in cardiac output (CO) in spite of the increase in myocardial contractility because the more decrease in venous return due to the more increase in blood pooling within the compliant tissues of the lower body. However, this is also unclear. To make these questions clear, the present study investigated the regional muscle mass and strength and orthostatic tolerance capacity before and after 20 days of bed rest in young subjects.     

Pharmacological model for airway hypersensitivity produced by propranolol and reserpine in guinea pigs

Combined treatment with propranolol and reserpine enhanced acetylcholine-induced doseresponse curves for bronchoconstriction in guinea pigs in vivo. This airway hyperreactivity model was investigated pharmacologically. (1) Increased capillary permeability and increases in leukocytes in bronchoalveolar lavage fluid (BALF) were not observed after this combined treatment. (2) The increased airway sensitivity to acetylcholine produced by propranolol and reserpine was inhibited by ketotifen and theophylline, reported in clinical studies to inhibit airway hyperreactivity. (3) Two leukotriene (LT) receptor antagonists, MCI-826 and FPL-55712, clearly inhibited this increased airway reactivity. (4) A thromboxane A₂ (TXA₂) receptor antagonist, ONO-3708, and TXA₂ synthetase inhibitor, OKY-046, also inhibited this increased airway reactivity.These results suggest that the airway hyperreactivity model produced by propranolol and reserpine in guinea pigs is a valuable pharmacological tool for investigating a remedy and LT and TXA₂ may be involved in the onset of this airway hyperreactivity.     

Effects of endothelin-1 and conversion of big endothelin-1 in the isolated perfused rabbit lung.

We examined the effects of endothelin-1 (ET-1) on pulmonary hemodynamic and transvascular fluid filtration and the conversion of big endothelin-1 (big ET-1), a precursor of ET-1, in isolated perfused rabbit lungs at constant vascular and airway pressures. Furthermore we examined whether ET-1 contributes to cyclooxygenase metabolism. The perfusate flow decreased significantly after bolus administration of 1 or 0.1 nmol of ET-1. Lung weight did not increase throughout the experimental period. Big ET-1- (1 nmol) induced decrease in the flow was slow in developing, although the maximum response was comparable to that induced by the same dose of ET-1. The concentration of bit ET-1 in the perfusate progressively decreased, while that of ET-1 increased in a time-dependent manner. Phosphoramidon, an inhibitor of metalloproteinase, suppressed the pressor effect of big ET-1 (P less than 0.01) and the increase in the concentration of ET-1 in the perfusate (P less than 0.05). The present findings provide the first evidence suggesting that the potent vasocontractile effect of big ET-1 in pulmonary circulation can be attributed to the production of ET-1 by the conversion from big ET-1 in the vascular bed. ET-1-induced perfusate flow changes were not affected by indomethacin, and the concentration of 6-ketoprostaglandin F1 alpha, a metabolite of prostacyclin, did not increase after ET-1 administration.     

Development of human cerebellar nuclei. Morphometric study

The morphometric development of the human cerebellar nuclei was examined in 9 fetuses (16-40 weeks of gestation; WG), an infant (2 months old) and 2 adults (16 and 63 years old). With the morphological observation of serial sections of the brain containing the cerebellar nuclei, the authors measured sections to get several morphometric parameters: the volume of nuclear column and number, packing density and cell body area of neurons. Each nucleus (dentate, emboliform, globose and fastigial nucleus) was recognized even at 16 WG. Nerve cells containing Nissl bodies were observed in all nuclei after 23 WG. Degenerative changes were detected in some neurons for every nucleus at 21 and 23 WG. Three stages were observed in the developmental course of nuclear volume and neuronal packing density: the primary or undifferentiated stage at 16 WG, the secondary stage with variability at 21-32 WG and the tertiary stage with monotonous increase (nuclear volume) or gradual decrease (neuronal packing density) after 35 WG. No significant correlation between neuronal number and gestational age was noticed for every nucleus. The analysis of cell body area (neuronal size) demonstrated that the dentate neurons developed after the intermediate or fastigial neurons. It is concluded that there is a critical period between slightly before 20 WG and slightly after 30 WG, matched with the secondary stage in the development of the cerebellar nuclei.