The effects of laminin on the growth and differentiation of embryonal carcinoma cells in defined media

In this paper we have examined the growth and differentiation of the embryonal carcinoma cell line, F₉, in the defined medium EM-3 at low density. We show that the growth of F₉ and their differentiated cells (F₉-diff) in EM-3 is strongly density dependent. At low cell densities the growth of both cell types is severely limited and most of the cells do not survive. Although this poses a problem for working with F₉ and F₉-diff in EM-3, it provides a convenient assay for identifying molecules that support their growth at low density. Using this assay, we have determined that laminin, a newly isolated glycoprotein of basement membranes, significantly improves the growth and short-term survival of both F₉ and F₉-diff. However, addition of laminin to EM-3 is insufficient to promote the clonal growth of these cell types. Our findings also indicate that laminin promotes the attachment of F₉ and F₉-diff in defined media. On the basis of our results, we propose an attachment function for laminin during the early stages of mammalian development.     

Self-titration by cigarette smokers

An 11-week crossover study was carried out in which 12 subjects smoked high-nicotine (1·84 mg standard yield) and low-nicotine (0·6 mg) cigarettes after an initial period of smoking their usual brands with a medium-nicotine yield (mean 1·4 mg). Plasma and urine nicotine concentrations, carboxyhaemoglobin (COHb) concentration, puffing behaviour, 24-hour cigarette consumption, and butt nicotine content were measured. The changes in plasma nicotine and blood COHb concentrations showed that the smokers compensated for about two-thirds of the difference in standard yields when switched to either high- or low-nicotine cigarettes. Thus, compared with the medium-nicotine brand, the intake of nicotine and carbon monoxide was only about 10% higher when subjects smoked the high-nicotine cigarettes, which had a standard yield 30-40% higher than the medium brands; and only about 15% lower when they smoked the low-nicotine cigarettes, which had a standard yield about 50% lower than the medium brands. But nicotine content and urine nicotine concentrations followed a similar pattern. Changes in puffing behaviour and in 24-hour cigarette consumption were only slight.The results show clear evidence of both upward and downward self-titration of nicotine and carbon monoxide (and tar) intakes when smokers change to cigarettes with standard yields that differ over the range studied.     

Composés bromés de Rytiphlea tinctoria (Rhodophyceae)

Four aromatic bromo compounds have been isolated from the ethanolic extract of Rytiphlea tinctoria after treatment with diazomethane: 2,4-dibromo-1,3,5-trimethoxy-benzene,5,6,3′,5′-tetrabromo-3,4,2′,4′,6′-pentamethoxydiphenylmethane, 5,6-dibromo-3,4-dimethoxy-benzyl alcohol and its ethyl ether. In addition to sterols, amino acids, this extract also contains quinonoid bromo-pigments which could play a rôle in photosensitisation of chlorophylls, a rôle normally taken by the phycobilins, in other Rhodophyceae.     

Explanations for weight loss after ileojejunal bypass in gross obesity.

Twenty grossly obese patients underwent ileojejunal bypass operations. Measurements of calories lost in faeces showed that the malabsorption could not account for the weight loss. Furthermore, the malabsorption was not decreased two years after bypass, when weight was no longer being lost. Dietary restriction is therefore largely responsible for the weight loss and increased food intake for weight maintenance.     

Stimulation of premature retinoic acid synthesis in Xenopus embryos following premature expression of aldehyde dehydrogenase ALDH1.

In order for nuclear retinoic acid receptors to mediate retinoid signaling, the ligand retinoic acid must first be produced from its vitamin A precursor retinal. Biochemical studies have shown that retinal can be metabolized in vitro to retinoic acid by members of the aldehyde dehydrogenase enzyme family, including ALDH1. Here we describe the first direct evidence that ALDH1 plays a physiological role in retinoic acid synthesis by analysis of retinoid signaling in Xenopus embryos, which have plentiful stores of maternally derived retinal. The Xenopus ALDH1 gene was cloned and shown to be highly conserved with chick and mammalian homologs. Xenopus ALDH1 was not expressed at blastula and gastrula stages, but was expressed at the neurula stage. We used a retinoic acid bioassay to demonstrate that retinoic acid is normally undetectable in embryos from fertilization to the initial gastrula stage, but that a tremendous increase in retinoic acid occurs during neurulation when ALDH1 is first expressed. Overexpression of ALDH1 by injection of Xenopus embryos with mRNAs encoding the mouse, chick or Xenopus ALDH1 homologs induced high levels of retinoic acid detection during the blastula stage. Thus, premature expression of ALDH1 stimulates premature synthesis of retinoic acid. These findings reveal an important conserved role for ALDH1 in retinoic acid synthesis in vivo, and demonstrate that conversion of retinoids from the aldehyde form to the carboxylic acid form is a crucial regulatory step in retinoid signaling.