Simulated microgravity increases myogenic tone in rat cerebral arteries

Adaptation ofthe cerebral circulation to microgravity was investigated in rat middlecerebral arteries after 20 days of hindlimb unweighting (HU). Myogenicresponses were measured in isolated, pressurized arteries from HU andcontrol animals. Maximal passive lumen diameters, obtained in theabsence of extracellular Ca²⁺ plusEDTA, were not significantly different between groups (249 vs. 258 µm). In physiological salt solution, arteries from both HU andcontrol animals maintained a constant lumen diameter when subjected toincremental increases in transmural pressure (20-80 mmHg).However, the diameter of arteries from HU animals was significantly smaller than that of arteries from control animals at all pressures; this difference could be eliminated by exposure to the nitric oxidesynthase inhibitorN^G-nitro-L-argininemethyl ester. After HU treatment, transient distensibility of theartery wall in response to pressure was also significantly decreased,whereas the frequency and amplitude of vasomotion were increased. Thelatter changes were not affected byN^G-nitro-L-argininemethyl ester. Thus simulated microgravity increases cerebral arterymyogenic tone through both nitric oxide synthase-dependent and-independent mechanisms.

     

The metabolism of benzene by bacteria. Purification and some properties of the enzyme cis-1,2-dihydroxycyclohexa-3,5-diene (nicotinamide–adenine dinucleotide) oxidoreductase (cis-benzene glycol dehydrogenase)

1. cis-Benzene glycol dehydrogenase was purified to a homogeneous state from a species of Pseudomonas grown with benzene as the major carbon source. 2. The enzyme was specific for the cis-isomer of its substrate and required NAD(+) as hydrogen acceptor. 3. Partial inactivation of the enzyme, which was observed during purification, could be reversed by the addition of Fe(2+) and GSH. 4. A molecular weight of 440000 was calculated from data obtained by sedimentation-velocity and diffusion analysis in the ultracentrifuge. Sodium dodecyl sulphate polyacrylamide-gel electrophoresis indicated a subunit of molecular weight 110000. 5. p-Chloromercuribenzoic acid and 1,10-phenanthroline were shown to inhibit the enzyme.     

Aplastic Anaemia,Acute Myeloblastic Leukaemia,and Oxymetholone

Four patients developed acute myeloblastic leukaemia after treatment of aplastic anaemia with oxymetholone. Two had previously shown an excellent clinical response to the drug and a third some improvement. Though no definite causal relationship between therapy and the onset of leukaemia has been established, the number of cases is greater than might have been expected by chance. The association of the two diseases is discussed.     

The mitochondrion of Plasmodium falciparum visualized by rhodamine 123 fluorescence

Rhodamine 123 (Rh123) has been used to probe the functional status of the mitochondrion present within the asexual, intraerythrocytic stages of the malarial parasite Plasmodium falciparum. This cationic fluorescent dye accumulates specifically in negatively charged cellular compartments, such as mitochondria. Using epifluorescence microscopy the development of what appears to be a single mitochondrion has been followed through the intraerythrocytic cycle. Mitochondrial development progresses from a fine thread-like organelle that becomes longer and eventually branched. Each daughter merozoite receives a branch or piece of the parent organelle. Cytoplasmic Rh123 accumulation was also observed, indicating that there exists a transmembrane potential across the outer plasma and parasitophorous vacuolar membranes of the parasite. The effects of uncouplers (protonophores), ionophores, and inhibitors were examined by monitoring Rh123 accumulation and retention. Our results demonstrate that the mitochondrion of P. falciparum actively maintains a high transmembrane potential, the function of which is as yet undefined.     

Growth of Aeromonas spp. at 4°C and related toxin production

Over the last few years Aeromonas spp. have been considered to be potential intestinal pathogens (Altwegg & Geiss 1989). Recently, detailed evidence has linked a strain from contaminated shrimp with a clinical isolate from a patient with diarrhoea and found them to be the same (Altwegg et al. 1991). It is now known that Aeromonas spp. are present in many foods, especially those of animal origin (Palumbo et al. 1989). Furthermore, previous studies have shown that these organisms are quite capable of growing at refrigeration temperatures. For example, Palumbo et al. (1985) found that seven out of 14 strains showed significant growth within 14 d at 5°C. However, most studies have only examined a relatively small number of strains, which were not speciated and were simply called A. hydrophila.
In this paper we examine the growth of 36 strains of aeromonas (divided into A. hydrophila, A. sobria and A. caviae ) at 4°C, and their ability to produce cyotoxins at 4°C, 30°C and 37°C.