Electrochemical Characteristics of Nitroheterocyclic Compounds of Biological Interest. VIII Stability of Nitro Radical Anions from Cyclic Voltammetric Studies

The stability of the one electron addition product of four biologically important nitroheterocyclic compounds has been examined electrochemically. Using cyclic voltammetry the tendency of the nitro radical anion to undergo disproportionation was studied by two methods of analysis. The first was based on determining the voltammetric time-constant required for half of the reduction product, RNO₂, to react further. The second concerned the minimum volume of dimethylformamide which had to be added to the aqueous electrolytic medium to give a specific cyclic voltammetric response. Both methods were found to compare well with the results obtained for RNO₂T stabilities using a theoretically derived procedure for a second order reaction following a charge-transfer step. The use of these alternative approaches for quantifying the reactivity of reduction products is discussed. The time-constant method in particular may be useful in studying complex reaction pathways.     

Female competition and reproductive success in northern elephant seals

The probability of weaning a healthy pup increases with age in female northern elephant seals, Mirounga angustirostris. On Año Nuevo Island, California, weaning success among ‘prime’ females, those 6 years of age or older, was more than double that of ‘young’ females, those 3 to 5 years old. Prime females were better mothers than young females because of superior size, higher social dominance, and greater maternal experience; they were more likely to mate with high-ranking males and gave birth at an optimal time and place, circumstances that maximized the probability that their pups would survive, develop, and reproduce. The competitive advantage of prime-age mothers over younger ones was greatest when female and pup density was high. Young females improved their chances of reproducing successfully by emigrating from crowded harems and establishing new colonies.     

Glucocorticoid binding to solubilized components of human placental trophoblast membranes

We have recently described glucocorticoid uptake by human placental membrane vesicles which is specific, saturable and has a low K (7 nM). This paper describes solubilization of these vesicles with Triton x-100 and successful demonstration of glucocorticoid binding to the putative transport site. This was accomplished by analysis of corticosterone binding to the 140,000 × g supernatant of solubilized vesicles using G-75 Sephadex chromatography. The amount of bound corticosterone present in the void volume was proportional to the concentration of solubilized vesicles. The specificity of binding was tested by coincubation of tritiated corticosterone with 100-fold excesses of various steroids. The relative ability of various steroids to inhibit binding was corticosterone=pregesterone- >aldosterone. Triamcinolone acetonide, and estradiol were ineffective competitors. We conclude from these studies that human placental membranes contain glucocorticoid-specific binding sites which can be solubilized with Triton x-100. It is possible that these sites are involved in membrane mediated transport of glucocorticoids by this tissue.     

Aminopyrine uptake by guinea pig gastric mucosal cells. Mediation by cyclic AMP and interactions among secretagogues

The role of cyclic nucleotides in regulating acid secretion by dispersed mucosal cells from guinea-pig stomach was examined by measuring first the ability of histamine and carbachol to stimulate [dimethylamine-14C]aminopyrine uptake and cyclic nucleotide metabolism and secondly, the effect of exogenous cyclic nucleotides on basal and stimulated [14C]aminopyrine uptake. The [14C]aminopyrine was found in an acidic, osmotically sensitive compartment, probably associated with the initial steps in acid secretion by these cells. Although histamine increased [14C]aminopyrine uptake and cyclic AMP synthesis as expected, histamine was approx. 10-fold more potent in inducing [14C]aminopyrine uptake. This dissociation of [14C]aminopyrine uptake and cyclic AMP metabolism process was further manifested by the observation that prostaglandin E1 failed to increase [14C]aminopyrine uptake, although it did cause a rise in cellular cyclic AMP. Furthermore, prostaglandin E1 did not alter the [14C]-aminopyrine uptake caused by histamine. Carbachol was found to increase the [14C]aminopyrine uptake and also to potentiate the ability of histamine to increase [14C]aminopyrine uptake. Carbachol, however, affected neither the histamine-induced increase in cyclic AMP nor the binding of [3H]histamine to the cells. Cimetidine, a histamine H2 receptor antagonist, blocked the [14C]aminopyrine uptake induced either by histamine alone or by the potentiating combination of histamine plus carbachol. These results suggest that cyclic AMP is mediating the action of histamine on [14C]aminopyrine uptake but changes in cyclic AMP per se are not necessarily the cause for the potentiated increase in [14C]aminopyrine uptake. Furthermore, the potentiated response observed with histamine plus carbachol on [14C]aminopyrine uptake occurs at a biochemical step distal to and not obviously related to cyclic AMP generation.     

Microfilament bundles in antheridial nuclei of Achlya ambisexualis E 87

This is the first report of intranuclear microfilaments within gametangial nuclei of oömycetous fungi. Longitudinal sections of four to six microfilaments were frequently observed in meiotic antheridial nuclei of Achlya ambisexualis. Each microfilament measured approximately 7–10 nm in diameter. Spindle tubules (25 nm in diameter) were also observed within some of the nuclei possessing microfilaments.     

Mutagenicity of organophosphorus compounds in bacteria and drosophila

140 Organophosphorus compounds (OP's) have been tested for mutagenic activity in bacteria, principally by using two specially constructed sets of tester strains of the bacteria Salmonella typhimurium and Escherichia coli. It was found that 20% gave positive mutagenic responses and that this group of chemicals produce base substitutions rather than frame-shift mutations. In most cases the DNA repair genes exrA⁺ and recA⁺ were for mutagenic activity.Seven compounds were further tested in Drosophila melanogaster for the ability to induce recessive lethal mutations. In some of these cases the doses administered to the flies had to be very low due to the highly toxic nature of the compounds. To overcome this problem, the accumulation of recessive lethal mutations was measured in populations which were continually exposed to the compounds over a period of some 18 months. During this time the populations developed increased resistance to the compound and so the dose administered could gradually be increased. Six of the compounds were mutagenic.Of the compounds tested in both systems, those showing mutagenic activity in bacteria were also mutaganic in Drosophila, those mutagenic in bacteria were not mutagenic in Drosophila.     

Immunological cost of chemical defence and the evolution of herbivore diet breadth

Selective pressures from host plant chemistry and natural enemies may contribute independently to driving insect herbivores towards narrow diet breadths. We used the specialist caterpillar, Junonia coenia (Nymphalidae), which sequesters defensive compounds, iridoid glycosides, from its host plants to assess the effects of plant chemistry and sequestration on the larval immune response. A series of experiments using implanted glass beads to challenge immune function showed that larvae feeding on diets with high concentrations of iridoid glycosides are more likely to have their immune response compromised than those feeding on diets low in these compounds. These results indicate that larvae feeding on plants with high concentrations of toxins might be more poorly defended against parasitoids, while at the same time being better defended against predators, suggesting that predators and parasitoids can exert different selective pressures on the evolution of herbivore diet breadth.