Exercise heart rates at different serum digoxin concentrations in patients with atrial fibrillation.

Heart rate at rest and during increasing workloads was measured in a double blind study of 12 patients with chronic atrial fibrillation when serum concentrations of digoxin were nil and at low and high therapeutic values. Twelve normal subjects were studied for comparison. The heart rate at all levels of exercise in most patients with atrial fibrillation was not adequately controlled by any serum digoxin concentration tested despite a reduction in heart rate with increasing serum digoxin concentrations. Control of the resting heart rate, even in patients with high serum digoxin concentrations, did not ensure adequate control of the heart rate during work rates equivalent to regular daily activities.     

The effects of mispair and nonpair correction in hybrid DNA on base ratios (G + C content) and total amounts of DNA

Base ratios and total DNA amounts can vary substantially between and within higher taxa and genera, and even within species. Gene conversion is one of several mechanisms that could cause such changes. For base substitutions, disparity in conversion direction is accompanied by an equivalent disparity in base ratio at the heterozygous site. Disparity in the direction of gene conversion at meiosis is common and can be extreme. For transitions (which give purine [R]/pyrimidine [Y] mispairs) and for transversions giving unlike R/R and Y/Y mispairs in hybrid DNA, this disparity could give slow but systematic changes in G + C percentage. For transversions giving like R/R and Y/Y mispairs, it could change AT/TA and CG/GC ratios. From the extent of correction direction disparity, one can deduce properties of repair enzymes, such as the ability (1) to excise preferentially the purine from one mispair and the pyrimidine from the other for two different R/Y mispairs from a single heterozygous site and (2) to excise one base preferentially from unlike R/R or Y/Y mispairs. Frame-shifts usually show strong disparity in conversion direction, with preferential cutting of the nonlooped or the looped-out strand of the nonpair in heterozygous h-DNA. The opposite directions of disparity for frame-shifts and their intragenic suppressors as Ascobolus suggest that repair enzymes have a strong, systematic bias as to which strand is cut. The conversion spectra of mutations induced with different mutagens suggest that the nonlooped strand is preferentially cut, so that base additions generally convert to mutant and deletions generally convert to wild-type forms. Especially in nonfunctional or noncoding DNA, this could cause a general increase in DNA amounts. Conversion disparity, selection, mutation, and other processes interact, affecting rates of change in base ratios and total DNA.      

Photoperiod influences the annual reproductive cycle of the male pallid bat (Antrozous pallidus)

Adult pallids bats collected in April or May, were maintained in short or long photoperiods (10 or 14 h light/day) for 3-6 months. In August, the short-day bats had regressed testes, epididymal spermatozoa and fully developed accessory sex glands, corresponding to the autumnal reproductive condition of field animals; long-day bats had testes undergoing spermatogenesis, few epididymal spermatozoa and undeveloped accessory sex glands (summer reproductive condition). Bats in each photoperiod manifested the expected autumnal reproductive pattern in October. We suggest that photoperiod influences the reproductive physiology of male pallid bats by affecting an endogenous circannual reproductive rhythm.     

Polymorphic Admixture Typing in Human Ethnic Populations

A panel of 257 RFLP loci was selected on the basis of high heterozygosity in Caucasian DNA surveys and equivalent spacing throughout the human genome. Probes from each locus were used in a Southern blot survey of allele frequency distribution for four human ethnic groups: Caucasian, African American, Asian (Chinese), and American Indian (Cheyenne). Nearly all RFLP loci were polymorphic in each group, albeit with a broad range of differing allele frequencies (δ). The distribution of frequency differences (δ values) was used for three purposes: (1) to provide estimates for genetic distance (differentiation) among these ethnic groups, (2) to revisit with a large data set the proportion of human genetic variation attributable to differentiation within ethnic groups, and (3) to identify loci with high δ values between recently admixed populations of use in mapping by admixture linkage disequilibrium (MALD). Although most markers display significant allele frequency differences between ethnic groups, the overall genetic distances between ethnic groups were small (.066–.098), and <10% of the measured overall molecular genetic diversity in these human samples can be attributed to “racial” differentiation. The median δ values for pairwise comparisons between groups fell between .15 and .20, permitting identification of highly informative RFLP loci for MALD disease association studies.     

Cardiovascular and metabolic responses to noradrenaline in men acclimatized to cold baths

The purpose of this study was to see whether artificial acclimatization to cold would reduce the pressor response to noradrenaline (NA) as natural acclimatization has been shown to do, and whether it would induce nonshivering thermogenesis. Three white men were infused with NA at four dosage levels between 0.038 and 0.300 g·kg^–1·min^–1 (2–23 g·min^–1), before and after artificial acclimatization to cold and again 4 months later when acclimatization had decayed. Acclimatization was induced by ten daily cold (15°Q baths of 30–60 min followed by rapid rewarming in hot (38–42°C) water, and was confirmed by tests of the subjects responses to whole-body cooling in air. Three control subjects also underwent the first and third tests. Acclimatization substantially reduced the pressor response to NA at 0.150 and 0.300 g·kg^–1·min^–1, confirming earlier findings by the same technique in naturally acclimatized men, and its decay increased this response to beyond its initial levels (P<0.05 for both changes). Acclimatization did not change the response to NA of heart rate, subjective impressions, skin temperature of finger and toe, pulmonary ventilation, or plasma free fatty acids and ketone bodies. At no time did NA increase oxygen consumption, or increase skin temperature or heat flow over reported sites of brown fat. These findings would seem to show that acclimatization to cold reduces sensitivity to the pressor effect of NA but does not induce nonshivering thermogenesis, and that the reduced sensitivity is replaced by a hypersensitivity to NA when acclimatization decays.     

Studies of trachoma in families on Taiwan.

This study was undertaken to clarify the natural history and pathogenesis of trachoma. A group of families who live in a formerly trachoma hyperendemic area of Southern Taiwan were placed under continuous surveillance. The development in recent years of the micro immunofluorescence test for trachoma antibody, along with improved cell culture isolation methods, have allowed this surveillance to include repeated effective laboratory studies in addition to clinical observations. After four years' study of one group of families and three years of another, a number of interesting findings have been obtained. Evidence is presented supporting our hypothesis that trachoma is a disease of immumopathology and results from repeated reinfections with the trachoma organisms. The clinical findings of papillae, especially those of an acute nature, has been the clinical finding most closely associated with the isolation of the organism and the demonstration of antibody. Evidence is presented that transmission of the organism is usually within the family group. Although only trachoma immunotypes B and C previously had been associated with trachoma infection on Taiwan, data is presented from one family in which type D infections occurred. While a series of new and reinfections with trachoma organisms were demonstrated in some of the families under observation, the majority of the families not only showed no new infections but showed spontaneous healing or disappearance of clinical and laboratory evidence of trachoma infection. This tendency of active trachoma infection to disappear from a family in the absence of transmission of the organism parallels the rapid fall and prevalence of active trachoma on Taiwan during the past decade.     

Filter and deposit: a potential role of freshwater mussels in ecosystem functioning associated with enhanced macroinvertebrate assemblage structure in a Neotropical river

Hydrobiologia - Mussels provide important ecological functions in freshwater ecosystems but the associations between Amazonian mussels, macroinvertebrate assemblage and habitat quality remain...