Failure of familiar males to prevent alien male-induced implantation block (the Bruce effect) in laboratory mice

Implantation failure in newly inseminated females induced by exposure to alien males (the Bruce effect) was significantly reduced when the females were housed with the stud male. By contrast, newly inseminated females housed with a familiar male during exposure to alien males exhibited a high rate of implantation failure. The results suggest that the protective effect of the stud male on implantation is not because of the familiarity of the female with his odour cues. The results are consistent with the view that the newly inseminated female mouse identifies her coital partner as an individual because she becomes 'imprinted' with his odour during the pericopulatory period.     

The role of C5 and T-cell receptor Vb genes in susceptibility to collagen-induced arthritis

Collagen-induced arthritis (CIA) is a rodent arthritis model in which immunization with heterologous type II collagen induces an inflammatory polyarthritis. Susceptibility to the disease is mediated by major histocompatibility complex (MHC) genes as well as genes at other loci. Previous studies of the SWR/J mouse strain, which is resistant to CIA despite bearing the susceptible H-2 ^q haplotype, have suggested that this resistance is the result of a deletion of T-cell receptor (Tcr) Vb gene segments which is carried by this strain. Other studies have implicated a deficiency in complement component C5 as the cause for the resistance. In order to assess the relative importance of these two genes in susceptibility to CIA, and to provide an estimate of the number of independent genes involved in the disease, we analyzed 196 F₂ progeny of a (DBA/1 × SWR/J) cross for arthritis susceptibility, and expression of both C5 and Tcr genes. Thirty of the F₂ progeny developed arthritis. All of the arthritic mice had at least one copy of the wild-type C5 allele, while the Tcr-Vb haplotypes were distributed in Mendelian fashion. These results demonstrate that C5 sufficiency is an absolute requirement for CIA, but that Tcr-Vb genes located within the SWR deletion have little influence. Genetic analysis of the incidence rate suggests that there is polygenic control of susceptibility to CIA and that in addition to H-2, 5–6 other independent loci (including C5) may be involved.     

Toxicity oft-butylhydroperoxide in hepatocyte monolayers exposed to hypoxia and reoxygenation

Summary Inasmuch as it is known that the toxicity of anesthetic agents is potentiated by hypoxia and that the reductive metabolism of these agents results in the formation of lipid hydroperoxides, we investigated the toxicity of hydroperoxides under low-oxygen concentrations. We found that hypoxia exacerbates the toxicity oft-butyl hydroperoxide, shifting the dose-response curve oft-butyl hydroperoxide vs. lysis of hepatocytes approximately an order of magnitude to the left. Furthermore, although at the end of a 4-h exposure to 0.5% O₂ hepatocyte monolayers seemed normal by three indices (release of⁵¹Cr and serum glutamate transaminase or exclusion of trypan blue), they were completely lysed after an additional 20 h reoxygenation at 20%. O₂. In contrast, monolayers exposed to 2% O₂ for 4 h seemed normal after 20 h reoxygenation. However, cells exposed to both a subtoxic dose of hydroperoxide and 4 h of 2% O₂, although seeming healthy at the end of the hypoxic period, were completely lysed within 20 h after reoxygenation. The study was supported by grant OH 00978 from the National Institutes for Occupational Safety and Health, Atlanta, Georgia.     

Accelerated transbilayer movement of phosphatidylcholine in sickled erythrocytes. A reversible process

The transbilayer mobility of phosphatidylcholine (PC) molecules in the membrane of homozygous reversible sickle cells (RSCs) was studied using a PC-specific exchange protein from beef liver. In deoxygenated RSCs, all of the PC present in the membrane of the intact cell is rapidly available for exchange, mediated by this protein. Since a substantial amount of the PC is present in the inner membrane leaflet of these cells, this observation implies that the PC molecules in their membranes do experience rapid transbilayer movements. To determine the actual rate of transbilayer movement of the PC, radioactive PC was introduced into the outer monolayer of oxygenated RSCs using the PC-specific exchange protein. Subsequently, the cells were incubated at 37 degrees C under oxy- and deoxygenating conditions to enable the PC to equilibrate within the bilayer. At various time intervals, samples were taken and treated with phospholipase A2, which selectively degrades the PC in the outer monolayer. Analysis of the specific radioactivities of the lyso-PC thus produced, as well as of the residual PC, enabled us to follow the fate of the radioactive PC previously introduced into the outer membrane layer. The half-time value for transbilayer equilibration of the PC in deoxygenated RSCs was determined to be 3.5 h, which is about four times lower than that for oxygenated RSCs. This increased transbilayer mobility of PC, observed in deoxygenated RSCs, is immediately restored to the normal low rate upon reoxygenation of the cells, indicating a complete reversibility of this phenomenon.     

M?ssbauer effect in the `super-reduced' form of the high-potential iron–sulphur protein from Chromatium (Short Communication)

Mössbauer-effect studies of the super-reduced form of Chromatium high-potential iron–sulphur protein indicate that the iron atoms are in a similar valency state to those in reduced ferredoxin from Clostridium pasteurianum, with possibly some inequivalence between the iron atoms within the four-iron centre. Mössbauer spectroscopy also shows magnetic differences between the four-iron centres in the two proteins.     

A calorimetric study of a polymer–monomer complex formed by polyuridylic acid 3′,5′-cyclic AMP

The existence of a soluble complex formed by polyuridylic acid (poly (U)) and 3′,5′-cyclic AMP (cAMP) is demonstrated by u.v. extinction vs. temperature curves, optical rotation, equilibrium dialysis, and reaction calorimetry. The complex hasthe stoichiometry of 2 poly (U)-cAMP and its formation is accompanied by an enthalpy change of ?13.0 kcal/mole of base triplet. The introuction of an empirical factor α in the equations given by Damle² and Crothers² leads to the evolution of a ΔH value of ?13.4 keal/mole. The parameter α is considered as a correction factor for the concentration dependence of the binding process. There is no relation between α and the reduction of monomer activity due to self-association of monomers. The study of the binding process at several temperatures showed that the cooperativity parameter, σ, is independent of temperature and its value of 6.5 × 10^?3 is in good agreement with σ = 5 × 10^?3 for the poly (U)·poly(A) system.³     

The cationic composition of incubated cerebral cortex slices

1. A new type of cutting table is described. It makes use of the elastic properties of a nylon thread, 0.08 mm thick, in which longitudinal vibrations greatly increase its ability to cut through soft tissue. Two slices of cerebral cortex may thus be obtained within 3-4 min after the death of an animal. 2. The extent of the swelling of a brain slice, as well as the ionic shift, is directly related to the amount of oxygen in the incubating fluid. Under the best conditions of oxygen supply, the swelling of a first slice was close to 12.2 +/- 4.3 per cent after 5 hr of incubation. The corresponding values for the Na+ and K+ contents were respectively 119.3 +/- 6.9 and 70.9 +/- 5.0 microequiv./g of final fresh weight (P2). 3. Incubation in complete anoxia leads to a considerable shift in the cation content of the slice, which acquires a composition close to that of the incubating fluid. This suggests that a large part of the cell population is still metabolically active when oxygen is present. 4. The inulin space represents 47.1 +/- 5.8 per cent of the initial fresh weight. It is independent of the amount of fluid taken up by the slice as well as of anoxia. 5. The cation content of the non-inulin space, calculated by assuming that the inulin space has the same composition as the incubation medium, was 77.7 microequiv./ml and 160.3 microequiv./ml for Na+ and K+ respectively. 6. The meaning of the inulin space, as well as the physico-chemical state of the cations in the slice, are discussed.