How costly is clutch formation in the Audouin's Gull Larus audouinii?

During the Audouin's Gull's breeding season at the Ebro Delta in 1993, 24 fresh eggs from eight three-egg clutches (modal clutch-size) were collected at the peak of the laying period. Eggs were processed to obtain formalin-fixed yolks, which were halved and stained using the potassium dichromate method. Digitized images of the yolks were examined to assess the daily rates of yolk deposition. We used these data in combination with egg compositional analysis to build a model of energy demands during the formation of an average clutch in Audouin's Gull. To show how the different parameters of clutch formation affect the daily energy investment peak, we performed a simulation analysis in which the rapid yolk development (RYD) period, the follicle triggering interval (FTI), the laying interval (LI) and the albumen synthesis period (ASP) were allowed to vary simultaneously. In our sample, the mean RYD period was seven days with a range from six to eight days. There were no significant differences in yolk volume among eggs in a clutch, but albumen volume was significantly smaller in third eggs. According to our model the albumen synthesis of the a-egg coincides with the energy demand peak for clutch formation. This peak represents an increase by ca. 42% in female energy requirements. Values obtained from the simulation analysis showed that only the ASP of the a-egg and the RYD durations of the second and third follicles produced noticeable reductions in peak energy investment. We predict that in gulls, whose laying intervals seem to be kept constant, significant increases of the durations of the RYD periods of second and third eggs, or even significant reductions of yolk size of these eggs, may operate simultaneously to match the energy demands during clutch formation to the prevailing food conditions.     

Characterization of a light-dependent glutamate synthase activity in Chlamydomonas reinhardtii

Photosynthetically active vesicles prepared from Chlamydomonas reinhardtii retained a light-dependent glutamate synthase activity which was highly specific for 2-oxoglutarate (K_m=2.1 mM) and L-glutamine (K_m=0.9 mM) as amido group acceptor and donor respectively. This activity was inhibited by azaserine, p-hydroxymercuribenzoate and 3-(p-chlorophenyl)-1,1-dimethyl urea.Light-dependent synthesis of glutamate was also obtained by coupling Chlamydomonas photosynthetic particles to purified ferredoxin-glutamate synthase, using ascorbate and 2,6-dichlorophenol-indophenol as electron donor. This system was also specific for 2-oxoglutarate (K_m=1 mM) and L-glutamine (K_m=0.8 mM) as substrates, and was stimulated by dithioerythritol. Azaserine and p-hydroxymercuribenzoate, but not 3-(p-chlorophenyl)-1,1-dimethyl urea, inhibited the reconstituted activity; high concentrations of 2-oxoglutarate were inhibitory.Abbreviations A Absorbance - CCP p-Trichlorometoxi-carbonylcyanide-phenylhydrazone - Chl Chlorophyll - CMU 3-(p-Chlorophenyl)-1,1-dimethyl urea - DPIP 2,6-Dichlorophenol-indophenol - DTE Dithioerythritol - MSX L-Methionine, D-L, sulfoximine - MV Methyl viologen     

A 45,X male with Y-specific DNA translocated onto chromosome 15.

A 20-year-old male patient with chromosomal constitution 45,X, testes and normal external genitalia was examined. Neither mosaicism nor a structurally aberrant Y chromosome was observed when routine cytogenetic analysis was performed on both lymphocytes and skin fibroblasts. Y chromosome-specific single-copy and repeated DNA sequences were detected in the patient's genome by means of 11 different recombinant-DNA probes of known regional assignment on the human Y chromosome. Data indicated that the short arm, the centromere, and part of the long-arm euchromatin of the Y chromosome have been retained and that the patient lacks deletion intervals 6 and 7 of Yq. High-resolution analysis of prometaphase chromosomes revealed additional euchromatic material on the short arm of one of the patient's chromosomes 15. After in situ hybridization with the Y chromosome-specific probe pDP105, a significant grain accumulation was observed distal to 15p11.2, suggesting a Y/15 chromosomal translocation. We conclude that some 45,X males originate from Y-chromosome/autosome translocations following a break in the proximal long arm of the Y chromosome.     

Immediate breast reconstruction: reducing the risks

One-hundred and sixty-five consecutive immediate breast reconstructions in 157 patients were reviewed. Reconstructions were performed with tissue expanders (53 percent) or immediate gel prostheses (47 percent). Immediate reconstruction was associated with an 18 percent rate of implant loss. Certain risk factors were identified at the p less than 0.05 level using immediate gel implants: failure to achieve complete muscle coverage of the implant, smoking at the time of surgery, initial gel implants of 400 ml or more volume, and age. Expander loss was increased by detaching the pectoralis major (p less than 0.05) and probably by lack of complete muscle coverage in general. Chemotherapy, history of previous smoking, and clinical stage of the carcinoma did not seem to affect reconstructive success. Smoking and patient age should be considered during patient selection for immediate reconstruction. Muscle coverage of the prosthesis should always be attempted. Muscle coverage is mandatory in the smoker. Gel implants of 400 ml or more volume are to be avoided at the initial operation. This approach should enable all surgeons to achieve lower rates of implant loss.     

Metabolic reduction of chromium,as related to its carcinogenic properties

At variance with Cr(III), Cr(VI) compounds easily cross cell membranes and exert genotoxic effects. No metabolic oxidation of Cr(III) could be detected, whereas Cr(VI) reduction was observed in the presence of body fluids and subcellular fractions of various tissues from several animal species. The differential efficiency of this process may account for the selection of target tissues in Cr(VI) carcinogenesis. For instance, reduction by saliva and gastric juice may explain a lack of carcinogenicity by the oral route; reduction inside erythrocytes may explain a lack of carcinogenicity at a distance from administration sites; reduction by the epithelial-lining fluid of terminal airways and by alveolar macrophages may be consistent with the occurrence of thresholds in lung carcinogenesis. Liver preparations displayed the top efficiency in reducing Cr(VI), whereas skeletal muscle, i.e., a typical target in experimental Cr(VI) carcinogenesis, had no detectable activity. Bronchial tree and peripheral lung parenchyma preparations from almost 100 individuals reduced Cr(VI) to a variable extent. The efficiency of lung parenchyma and of isolated alveolar macrophages was enhanced in cigarette smokers. In rats, Cr(VI) reduction by lung preparations was significantly stimulated by the repeated i.t. instillation of Cr(VI) itself. Among the electron donors (chiefly GSH) and enzymatic mechanisms responsible for the intracellular Cr(VI) reduction, such as cytochrome P-450 reductase, glutathione redactase, and aldehyde oxidase, an important role can be ascribed to cytosolic DT diaphorase activity, usually catalyzing a 2-electron reduction.     

In vitro interaction of mutagenic chromium (VI) with red blood cells

The interaction of mutagenic Cr(VI) with red blood cells has been studied by ESR spectroscopy. Signals of two Cr(V) species are observed almost immediately after contacting red cells with chromate(VI) aqueous solution at pH 7.4. The signal at go = 1.985, which decays within one hour, is attributed to a Cr(V) complex formed by glutathione due its reducing and chelating ability. The other signal at go = 1.979, which is distinctly more persistent, may indicate that some immobilization of the formed Cr(V) ions takes place on the macromolecular cell components, e.g. glycoproteins.     

Size variation in Brachionus plicatilis resting eggs

The effect of temperature and salinity on resting egg size of two Brachionus plicatilis (Rotifers) clones was investigated. Clones were selected according to their different behaviour in laying resting eggs: one clone ejects them, whereas they remain inside the females body in the other clone. The difference in resting eggs size between the two clones is noticeable, although the difference is not as great as that between female body size. An important temperature-salinity interaction on resting egg size has been observed. The general inverse relationship between size and temperature is only true at lower temperatures. At high temperatures size varies around the mean although could be greater than at intermediate temperatures. This is more evident at the intermediate salinity tested which is considered to be the closest to the optimum in our experiments. This pattern of variation suggests that mean size is bigger than expected, in relation to temperature and salinity, when these factors have values close to the extremes of their range, normally found in nature, and to which adaptative mechanisms can evolve. Size is bigger at the salinity — temperature low - low and high - high combinations which are the most commonly found in the temperate environments.     

Inhibition of gastric acid secretion by peptide YY is independent of gastric somatostatin release in the rat

The purpose of this study was to determine whether the inhibitory action of peptide YY (PYY) on gastric acid secretion is attributable to the release of gastric somatostatin in rats. Two groups of rats (six rats/group) were anesthetized with urethane and prepared with gastric fistulas and jugular catheters. Pentagastrin (18 micrograms/kg-h) was given intravenously for 150 min to stimulate gastric acid secretion. Intravenous PYY (130 micrograms/kg-h) inhibited pentagastrin-stimulated gastric acid secretion significantly (P less than 0.05). Administration of iv PYY resulted in a 41% reduction (P less than 0.05) in pentagastrin-stimulated gastric acid secretion. In another group of anesthetized rats, administration of PYY (10(-7), 10(-8) M) failed to stimulate a release of somatostatin from the isolated-perfused rat stomach. Our findings indicate that PYY can inhibit gastric acid secretion independently of release of gastric somatostatin in the rat.     

The distribution of A1 adenosine receptor and 5′-nucleotidase in pig brain cortex subcellular fractions

Pig brain cerebral cortex was subfractionated by isopycnic centrifugation in sucrose gradients. In each subfraction the content of the agonist [³H]R-PIA binding, the activity of adenosine metabolizing enzymes (5-nucleotidase and adenosine deaminase) and the activity of membrane marker enzymes were determined. The fractions were also examined by electron microscope. In general, the results suggest a widespread distribution of A₁ adenosine receptors in membranes from different origins. Marker enzyme profile characterization indicated an enrichment of A₁ adenosine receptor in pre-synaptic membranes isolated from the crude synaptosomal fraction (P2B subfraction) as well as in membranes of glial origin such as myelin. The receptor is also present in the endoplasmic reticulum and in membranes isolated from the microsomal fraction that seem to have a post-synaptic origin (P3B). In subfractions having a high content of adenosine receptor the equilibrium binding paramters were obtained as well as the proportion of high- to low-affinity sites. From the values of the equilibrium constants it was not possible to find differences between the receptor in the different subfractions. Analysis of the affinity state distribution showed a diminished percentage of high-affinity sites in fraction P3A, which can be accounted by the existence of myelin membranes; in contrast the percentage of high-affinity states was higher in P2 and P3B, indicating that in these fractions the receptor is present in synaptosomal membranes. The close correlation shown between the enzyme 5-nucleotidase specific activity and the specific ligand binding distributions led us to postulate an important role for the enzyme in the regulation of adenosine action in pig brain cortex.     

Effect of hypothyroidism on the biogenesis of free mitochondria in the cerebral hemispheres and in cerebellum of rat during postnatal development

The effect of propylthiouracil-induced neonatal hypothyroidism on some aspects of the biogenesis of free (non-synaptosomal) mitochondria in the cerebral hemispheres and in the cerebellum of developing rat has been studied. The results obtained show that in hypothyroid rats mitochondrial DNA synthesis is delayed, mitochondrial RNA synthesis is not affected and cytochrome aa₃ content of mitochondria is lower than in controls. Furthermore ultrathin sections of 14-and 21-day old hypothyroid rat cerebella show mitochondria with an altered ultrastructural organization and large intracristal spaces.