Haversian bone remodelling in human fetus

Haversian bone remodelling used to be considered an attribute of adult bone. In the present paper, typical haversian remodelling was observed in the humerus, ulna, radius, femur, tibia, fibula and 6th and 7th ribs as soon as the 24th week. Its aspect suggests an already ancient occurrence. Remodelling was found in the same bone pieces of the neonate as well as in the clavicle and the other ribs. Mechanical factors may be responsible for starting the remodelling but their effects could be modulated by metabolic needs. Other still unknown factors might play a role too.     

Effects of dexamethasone on carnitine metabolism in liver and extrahepatic tissues

The in vivo effects of dexamethasone administration on liver and extrahepatic tissue carnitine concentrations were assessed in 48-h-starved rats. In heart and kidney, but not in liver, dexamethasone significantly increased total carnitine concentration. Acute (2.5 h) treatment with 2-tetradecylglycidate (TDG), a specific inhibitor of carnitine palmitoyl transferase 1, not only increased total hepatic carnitine concentrations, but also permitted an effect of dexamethasone (a further increase in hepatic carnitine concentration). The results are discussed in terms of acute (substrate-mediated) and chronic (hormonal) control of carnitine turnover.     

Population structure of the intertidal copepod Tigriopus californicus as revealed by field manipulation of allele frequencies

Summary Allele frequencies in natural T. californicus populations were perturbed by introduction of copepods from neighboring differentiated populations. In five experiments, the Gpt ^F allele was introduced into single recipient pools at a frequency of approximately 20%. In each case, the introduced allele declined to low frequencies (<3%) in less than one month, apparently due to dilution by residents of other pools on the same outcrop. In a larger scale experiment, the Pgi ^F was introduced into four pools on a single small rock outcrop; all pools on the outcrop were subsequently monitored. While the allele frequency fell from approximately 40% to 10% during the first six weeks after the transplant, no further change in frequency was observed for the duration of the experiment (16 months). Within six weeks some spread of the allele to non-recipient pools on the same outcrop was observed; by eight months, allele frequencies in all pools on the outcrop were similar. Hence, despite the extensive turnover of subpopulations as single pools evaporate or are washed out, genetic homogeneity and stability of entire outcrops are maintained via extensive inter-pool gene flow; this contrasts sharply with the highly restricted levels of inter-outcrop gene flow.     

Synthesis of fibronectin in normal and osteoarthritic articular cartilage

The content and the biosynthesis of fibronectin was examined in disease-free articular cartilage and in articular cartilage from osteoarthritic canine joints. Fibronectin content was increased in extracts of cartilage from osteoarthritic joints. Incubation of cartilage in vitro with [³H]phenylalanine and subsequent isolation of [³H]fibronectin from a gelatin affinity column and characterization by SDS-polyacrylamide gel electrophoresis and by immunoprecipitation indicated that disease-free and osteoarthritic cartilage explants synthesized fibronectin. About 50% of the [³H]fibronectin was recovered in the incubation medium. The osteoarthritic cartilage synthesized and accumulated up to 5-fold more [³H]fibronectin than disease-free cartilage.     

Purification and properties of human placental acid lipase

Two peaks of lysosomal acid lipase activity were purified from normal human placenta. Acid lipase I, with an estimated molecular weight of 102 500, was purified 1016-fold while acid lipase II, with an estimated molecular weight of 30 600, was purified 3031-fold. The final yields of enzyme activity for acid lipase I and II were 0.9% and 2.2% respectively. The purity of the final preparations was documented by demonstration of a single protein band on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Both preparations of the purified enzyme demonstrated activity towards triolein, cholesteryl oleate and the artificial substrate 4-methylumbelliferyl oleate. Examination of Km values, thermal stability, pH optima, and electrophoretic mobility revealed similar properties for the two enzyme peaks. The response of the two enzyme preparations to inhibitors was similar with both being significantly inhibited by 0.2 M NaCl, 0.2 M KCl, 5 mM HgCl2 and 5 mM p-chloromercuribenzoate. The activity of the two preparations as assayed with either triolein or cholesterol oleate was not significantly affected by the addition of bovine serum albumin. In contrast, the 4-methylumbelliferyl oleate activity of both preparations was significantly inhibitred by albumin. These findings support the hypothesis that the same enzyme or enzymes are responsible for the intralysosomal hydrolysis of triacylglycerols and cholesterol esters in human tissues.