The effects of DDT and its analogs upon lecithin and other monolayers

The effect of DDT, 11 analogs, dieldrin, and lindane was studied on the pressure-area curves obtained by compressing monolayers of lecithin. The minimum cross-sectional area of lecithin and the compounds was measured by photography of models. All compounds shifted the pressure area curves in a direction and to an amount that suggested they formed 1:1 complexes with lecithin, and the complex had the cross-sectional area of the compound. DDT did not complex with cholesterol monolayers. Both DDT and DDMU formed complexes with phospholipids from Torpedo electroplax which resembled those with lecithin. The lack of difference in effects on monolayers between physiologically active and inactive analogs indicated that the monolayer effects did not explain the physiological action of DDT.     

The structure-activity relationship of DDT analogs in crayfish giant axons

The effects of 14 DDT analogs on the resting and action potentials of the crayfish giant axon were investigated using the intracellular microelectrode technique. These analogs can be classified into three groups, excitatory, blocking, and dualist. An excitatory analog tends to increase the excitability of the axonal membrane, and has hydrophobic side chains on the para positions whose optimal size equals that of the ethoxy group. A blocking analog suppresses the action potential without affecting the resting potential, and has hydrophilic side chains capable of forming hydrogen bonds. A dualist has both excitatory and blocking actions, and the latter may be related to restriction in rotation imposed by the grouping on the benzylic carbon. However, the dividing lines between these categories are not sharp, the compounds tending to fall along a spectrum between pure excitatory and pure blocking activity.     

Quantitative structure-activity relationship of DDT analogs

A quantitative structure-activity relationship (QSAR) has been carried out for Phormia regina toxicity by a set of 24 p,p′-disubstituted analogs of DDT. The toxicity data are from the extensive studies of R. L. Metcalf. Preliminary examination of the data indicated that toxicity was parabolically related to molar refractivity, MR, of the ring substituents. This enabled parabolic regression to be evaluated. Multiple regression analysis relating toxicity and the substituent constants MR, Taft steric parameter (E_s), hydrophobicity (π), and polar effect (σ) showed that MR dominated the regression equations. The implication of these physicochemical properties in the interaction of DDT analogs with the receptor site is discussed.     

The effects of DDT upon flat and vesicular bilayers studied by a fluorescent probe

The effect of DDT and several analogs upon bilayer membranes was studied, using the fluorescent dye di (octadecyl)oxycarbocyanin as a probe. It was shown in flat bilayers of Torpedo electroplax phospholipids, using fluorescence correlation spectroscopy, that neither DDT nor its physiologically inactive analog, p,p′-hydroxy-DDT, affected the fluidity of the membrane. However DDT, and not the analog, displaced half of the dye from the membrane. In studies with lecithin or Torpedo electroplax phospholipid vesicles, using simple fluorescence measurements, no displacement of the dye was observed by DDT or its analogs.     

Insecticidal and neuroexciting actions of DDT analogs

The neuroexciting activity of DDT and its analogs to produce repetitive responses on the nerve cord of Periplaneta americana was determined using the extracellular electrode method. The convulsive activity on P. americana and the insecticidal effect on Callosobruchus chinensis were also examined. It was found that the convulsive and insecticidal activities increase almost proportionally with increase in the neuroexciting activity within a set of p,p′-substituted DDT analogs. The intimate connections among these biological effects suggest that symptoms such as convulsion and death caused by DDT analogs are closely related with their neuroexcitory effect and there is a common mode of action in spite of differences in insect species.     

Anaerobic metabolism of DDT analogs by pigeon liver preparations

The amounts of p,p′-DDT and of five other trichloroethane derivatives decreased upon incubation under anaerobic conditions with 12,000g × 30 min pigeon liver supernatant fraction. The addition of an exogenous NADPH-generating system sometimes, but not invariably, increased the rate of metabolism. Only one hexane-soluble metabolite was detected in the postincubation reaction medium of each of the six trichloroethane derivatives. After isolation by tlc the six metabolites were shown by mass spectrometry to have molecular weights 34 units less than their parent compounds. Comparison of the isotope patterns in the spectra of each substrate and its metabolite reveals that in each case the metabolism involves the loss of a chlorine atom. From these data it is concluded that several substituted trichloroethanes undergo reductive dechlorination when they are incubated with liver preparations in an atomosphere of nitrogen. Two dichloroethane derivatives, tested in a similar manner, were unchanged and were recovered quantitatively. Mass spectrometric and chromatographic data of reactants and products are recorded.     

In vitro effects of DDT analogs on trout brain Mg2+-ATPases: Inhibition kinetics

A continuous in vitro steady-state assay procedure was used to investigate the dependence of trout brain mitochondrial Mg²⁺-stimulated adenosinetriphosphatase specific activity on temperature and substrate concentration. The inhibition of enzyme activity by DDT was independent of substrate concentration. DDT and several analogs caused increases in the experimental activation energy and frequency factor of the enzyme-catalyzed reaction, which gave rise to a negative temperature coefficient of inhibition. It is suggested that DDT and other highly lipophilic compounds have the potential to allosterically affect membrane-bound enzymes by simply becoming a major lipoid component of the membranes.     

The effect of DDT and its analogs on the fragility of human erythrocytes

The antihemolytic actions of DDT and eight analogs were examined with human erythrocytes. Apparent aqueous concentrations to produce 60% of control hemolysis ranged from 3.7 × 10^?4 to 2.4 × 10^?6M, with DDT being one of the least active. No correlation was found between antihemolytic potency and neurotoxicity, and it was concluded that the findings did not illuminate the toxic or neural actions of these compounds.     

The sensitivity of mitochondrial Mg2+ ATPase to DDT and analogs at different temperatures

Oligomycin-sensitive (O-S) Mg²⁺ ATPase from American cockroach muscle was more sensitive to DDT, TDE, methoxychlor, and DDE at cool temperatures than at warm temperature, thus showing a negative temperature effect. In contrast, inhibition by acaricides dicofol, chlorfenethol, and Plictran shows a positive temperature effect. Oxidative phosphorylation in a mitochondrial preparation from cockroach coxal muscle was reduced by DDT, but the reduction was greater at a higher temperature (32°C) than at a cooler temperature (22°C). In addition, Na⁺K⁺ ATPase from cockroach nerve cord showed a positive temperature effect with DDT. The inhibition by DDT was much less on Na⁺K⁺ ATPase than on O-S Mg²⁺ ATPase. The negative temperature effect by DDT and analogs on O-S Mg²⁺ ATPase parallels toxicity effects on insects and fish as reported by numerous researchers. The results provide further evidence for this energy-regulating enzyme being a critical component in the biological action of DDT.     

The effect of some DDT and methoxychlor analogs on temperature selection and lethality in brook trout fingerlings

The effects of several DDT and methoxychlor analogs on trout fingerling temperature selection and lethality were investigated. The molecular requirements for lethality and alteration of temperature selection were different. Only p, p′-DDT, p, p′-DDD, and p, p′-methoxychlor were toxic in the range 10–50 ppb used. All the compounds tested, except DDE-type analogs, altered temperature selection. The effect of p, p′-methoxychlor on temperature selection progressively decreased until normal values were obtained 5 days after exposure. The effect of p, p′-DDT was still pronounced 9 days after exposure.     

Kinetics of sodium channel modification as the basis for the variation in the nerve membrane effects of pyrethroids and DDT analogs

The effects of a wide range of pyrethroids and DDT analogs on the membrane potential and membrane sodium currents were studied in crayfish giant axons. Compounds differed greatly in their ability to produce depolarizing afterpotentials, repetitive firing, and membrane depolarization. The differences observed at the membrane potential level could be explained by differences in the kinetics with which the insecticides interact with the nerve membrane sodium channel. The compounds containing a cyano group at the α position retain sodium channels in a modified open state persistently, depolarize the membrane, and block the action potential without causing repetitive firing. The pyrethroids without an α-cyano group and DDT analogs retain sodium channels in a modified open state only transiently, cause large depolarizing afterpotentials, and evoke repetitive firing with minimal effect on the resting potential. The effects of the phenoxybenzyl pyrethroids were found to be intermediate between these two extremes suggesting that a continuous variation exists in kinetics with which pyrethroids and DDT analogs modify sodium channels. It was not necessary to assume a second site of action to account for the variability observed. The implications of these results to the construction of quantitative structure-activity relationships is discussed.     

Effects of DDT on electrical properties of lecithin-decane bilayer membranes

Lecithin-decane bilayer membranes were treated with DDT and valinomycin, either by adding the compounds to the electrolyte around the membrane or by adding them directly to the lecithin-decane. Membrane capacitance was calculated using the dc transient technique. Specific capacitance was determined from capacitance versus area regressions and was not significantly altered by DDT. Specific K⁺ conductance was decreased by DDT, but only when DDT and the K⁺ carrier, valinomycin, were administered to the electrolyte where they may have interacted hydrophobically. It is concluded that the valinomycin-induced conductance of artificial membranes is inappropriate as a model for investigating the effects of DDT on the electrical properties of excitable membranes.     

The effects of DDT and dieldrin on rat peritoneal macrophages

The effects of DDT and dieldrin on cell population, viability, and phagocytic activity on the rat peritoneal macrophages were studied. It was observed that both pesticides, at low levels of concentration, exhibited a marked effect on this cell type. At the lowest concentrations tested both pesticides produced an increase in the macrophage population which appeared to be the result of a foreign-body response. At higher concentrations of pesticide this foreign-body response appears to be inhibited. The phagocytic activity of the cells steadily decreased as the concentration of the pesticide administered increased, and a decrease in cell viability with increased pesticide exposure was also noted.     

In vitro effects of DDT analogs on trout brain Mg2+-ATPases: I. Specificity and physiological significance

A continuous steady-state assay procedure was used to investigate the effects of DDT and several analogs on the in vitro Mg²⁺-stimulated adenosinetriphosphatase of a trout brain mitochondrial fraction. Pharmacological dissection of the enzyme with oligomycin, dicyclohexyl-carbodiimide, and azide failed to yield a fraction specifically sensitive to the organochlorines. At 25°C, low doses of DDT (≤1.35 μmol/mg of protein) stimulated enzyme activity, while methoxychlor was stimulatory at all doses. Higher doses of DDT and of several analogs caused only 45.5% or less inhibition at 25°C, but inhibition increased at lower temperatures. The physiological significance of these effects is discussed.     

The effects of some organochlorine pesticide analogs on salmonid brain ATPases

The effects of various organochlorine pesticides on salmon and trout brain ATPases were investigated. Organochlorines reduced the enzyme activity to various degrees, but only at concentrations which exceeded their solubility limits. When organochlorine precipitation was prevented by introduction of a surfactant, the reduction in enzyme activity was usually abolished.     

Mechanism of DDT resistance in larvae of the mosquito Aedes aegypti L.; The effect of DDT selection

Selection with pp'-DDT was applied to fourth-stage larvae of Aedes aegypti along four lines, starting with larvae of the F₂ generation from crosses between a susceptible strain and each of four resistant strains (two of Trinidad origin and two of Bangkok origin). Larval resistance increased substantially along each line but there was little or no change in the percentage breakdown of DDT to 1,1-dichloro-2,2-bis(4-chloro-phenyl)ethylene (pp'-DDE) in vivo and in no line were these two variables significantly correlated. Percentage breakdown was generally higher at 10 mg than at 50 mg litre^?1. DDT uptake (defined as content of DDT+pp'-DDE) was generally higher after exposure to 50 mg than to 10 mg litre^?1. It increased significantly with selection in the TE×NS line; it remained unchanged in the T8 × NS line; and in the other two lines (BSJ × NS and B51 × NS), it increased initially but dropped as selection progressed, the reduction being highly significant in the second of these lines. The amount of internal residual (unmetabolised) DDT tolerated by larvae of the TE × NS line also increased significantly with resistance. The levels in the other lines followed the pattern of uptake, remaining steady in T8 × NS despite the increase in survival, rising at first and then declining in the two Bangkok lines. Thus selection produced a higher tolerance to internal unmetabolised DDT in the two Trinidad lines but led ultimately to a lower content of DDT+pp'-DDE in the two Bangkok lines. The reasons for this behaviour are discussed.     

Effects of reducing DDT usage on total DDT storage in humans

Agricultural uses of the insecticide DDT were cancelled by the U.S. Environmental Protection Agency December 31, 1972. However, the domestic use of DDT had begun to decline before this action. Beginning July 1969, residues of DDT and its metabolites were measured in human adipose tissue collected through an annual national survey. Levels of total DDT equivalent residues in human adipose have decreased slightly, but the frequencies of finding DDT or its metabolites have remained high. The most marked decline in residue concentration has been found in the youngest age group (0-14 years). Approximately 80 percent of the total DDT equivalent found in this survey was DDE. These data show that the reduction of the agricultural uses of DDT has decreased human exposure to and storage of this chemical.     

Residues of DDT in cottonseed after spraying with DDT and torbidan

DDT at 1.12 and 2.24 kg/ha a.i. and Torbidan at 5 and 10 litre formulation/ha (1 and 2 kg DDT/ha) were sprayed five times on cotton over a period of 15 weeks. Seeds from the first pick of the crop were found to contain as residues pp′-DDT and pp′-DDE [1,1-dichloro-2,2-di- (4-chlorophenyl)ethylene]. The highest residue level (0.783 parts/10⁶) was found in seeds from Torbidan 10 litre/ha treatment.     

Effect of isopropyl-3-chlorocarbanilate and isopropyl-3-chlorohydroxycarbanilate analogs upon oxidative phosphorylation in plant mitochondria

The effects of the herbicide, isopropyl-3-chlorocarbanilate, and its hydroxylated metabolites, isopropyl-5-chloro-2-hydroxycarbanilate and isopropyl-3-chloro-4-hydroxycarbanilate, upon NADH oxidation, P_i uptake or release, and ATP formation were studied in corn mitochondria. The results indicated that 0.1 mM isopropyl-3-chlorocarbanilate and the 2-hydroxy-metabolite inhibited NADH oxidation by 30% whereas only the 2-hydroxy-metabolite inhibited NADH-linked ATP formation (85–100%). Dinitrophenol and the 2-hydroxy-metabolite exerted similar effects upon respiration, phosphorylation, and ATPase activity. The 4-hydroxy-metabolite (0.1 mM) exerted no effect upon respiration, phosphorylation, or ATPase activity. The β-O-glucoside conjugates of the hydroxymetabolities of isopropyl-3-chlorocarbanilate did not inhibit NADH-linked respiration or phosphorylation at 0.1 mM concentrations. Comparative studies with corn, cucumber, and soybean mitochondria indicated that the parent herbicide and its metabolites affected respiration and phosphorylation activities in a similar manner.     

Comparative metabolism of six ethoxychlor analogs and DDT in DDT-resistant and susceptible strains of the house fly Musca domestica L

The metabolic fate of six ³H-ring-substituted ethoxychlor analogs with altered aliphatic moieties and [¹⁴C]p,p′-DDT was investigated in susceptible and DDT-resistant strains of the house fly Musca domestica Linnaeus. The chloroalkane analogs, dichloroethane, chloropropane, and dichloropropane were primarily metabolized to the corresponding dehydrochlorinated products. This pathway was relatively more prominent in the resistant strain than in the susceptible strain. Biotransformation and detoxication of the isobutane, nitropropane, and neopentane derivatives was through microsomal oxidation (O-deethylation) of aryl ethoxy degradophores, and oxidation of the aliphatic moieties to produce the corresponding benzophenones, with no substantial differences between the resistant and susceptible strain. There was a strong correlation between the Taft ($\text{σ}{}^1$) values for the altered aliphatic moieties of chloroalkane analogs and their rate of dehydrochlorination in both the strains. These results suggest the importance of altered aliphatic moieties in developing resistance-proof DDT derivatives.