Isometric effects on treadmill exercise response in healthy young men

This study evaluated the hypothesis that the isometric stress of load carrying augments the dynamic exercise response seen on the treadmill, and estimated the magnitude of this effect on heart rate and blood pressure for several methods of carrying the same load. Thirteen healthy subjects carried 40 lb in the right hand (H), 40 lb on the back (B), 20 lb in each hand (D) and no weight (N) while walking for 3 minutes on the treadmill at a grade of 0 at 1.7 miles/ hour. A statistically significant increase in the rate of rise and peak levels of systolic blood pressure, heart rate, estimated mean blood pressure, the product of estimated mean blood pressure and heart rate and systolic blood pressure-heart rate product was shown when task H was compared with tasks B, D and N. Values for tasks D and B did not differ significantly.The effects of isometric and dynamic exercise combined were greater than those of dynamic exercise alone. An effective technique of load distribution reduced the rate of increase in blood pressure, heart rate and the peak attained during dynamic exercise, thereby suggesting a lower level of myocardial oxygen consumption for a given weight-carrying task. These results can be applied to evaluation of patients with heart disease and estimation of their exercise tolerance.     

Echocardiography in chronic alcoholics following prolonged periods of abstinence

Left ventricular function was analyzed using standard echocardiographic techniques in 26 chronic asymptomatic alcoholics without clinical evidence of cardiovascular disease. All were studied following a long period of abstinence (mean 3.1 years; range 3 months to 17 years). Seven asymptomatic children (mean age 14.1 years; range 4 to 19 years) whose mothers had been actively drinking throughout their pregnancies were also studied. The calculated fractional shortening of the left ventricle (per cent ΔS), ejection fraction, mean velocity of circumferential fiber shortening (mean V_CF), excursions and maximal systolic velocites of the ventricular septum and left ventricular posterior wall, preejection period/left ventricular ejection time ratios, mitral valve EF slopes, and thicknesses of the left ventricular posterior wall and ventricular septum were obtained in all. Normal left ventricular function was found in all but one adult alcoholic. In this patient, the per cent ΔS, ejection fraction, and mean V_CF were reduced. One additional adult alcoholic had a minimally thickened ventricular septum. Our results differ from other studies which have shown significant left ventricular dysfunction in asymptomatic chronic alcoholics. A possible explanation is the much longer period of abstinence of our chronic alcoholics at the time of their examinations. It also appears that left ventricular function in children born of alcoholic mothers is not affected when assessed after the long interval following prolonged exposure to alcohol in utero.     

Genital human papillomavirus infection in Panama City prostitutes

Little is known of the natural history of genital human papillomavirus (HPV) infections in women from high-risk populations. Samples were collected from 183 Panama City prostitutes and assessed for HPV (filter in situ DNA hybridization) and for sexually transmitted agents. The cohort was followed for 8 mo; 51% of subjects completed four monthly return visits and 16% were sampled eight times. The proportion of women found infected with HPV increased significantly with increasing numbers of consecutive samples tested; 38 (21%) of 183 women were positive after one visit and 46 (82%) of 56 who completed six visits were infected. The pattern of viral detection over time was not random, which implied that most prostitutes were persistently infected with genital HPVs and that either scattered foci of infection or periodic reactivation of latent virus occurred. Our findings suggest that multiple sampling is necessary to accurately estimate HPV infection rates and to define whether patterns of DNA expression are present.     

CO uptake kinetics of red cells and CO diffusing capacity.

The rate at which CO displaces oxygen from combination with hemoglobin in intact red cells was measured spectrophotometrically in whole blood thin films that minimize unstirred layer extra-cellular diffusion barriers. A step-change was made in CO tension from zero to one of four values (2, 7, 21 and 70 Torr) during a constant background of one of eight O2 tensions (0, 40, 70, 100, 153, 214, 285 and 428 Torr). For PO2 greater than 100 Torr measured red cell initial CO uptake rates were compared with calculated rates at the same PCO-PO2 based on the Gibson-Roughton rate equation (Gibson and Roughton, Proc. R. Soc. B 143: 310-334, 1955) for a well mixed Hb solution. Measured CO uptake rates expressed as initial rate of saturation change (delta S/delta t) quantitatively followed the theoretical rate equation (time in seconds) [sequence: see text] These measurements provide new values for theta CO, the specific conductance of whole blood (ml.min-1.Torr-1; PCO, PO2 in Torr): [sequence: see text] These results signify that in vivo, in normoxia and hyperoxia, red cell CO uptake rate is wholly reaction rate limited and that pulmonary capillary red cell CO diffusion equilibrium is rapidly achieved. The Bohr-Krogh assumption that red cell PCO = 0 during CO uptake is untrue.     

Sodium-calcium ion exchange in cardiac membrane vesicles.

Membrane vesicles isolated from rabbit ventricular tissue rapidly accumulated Ca2+ when an outwardly directed Na+ gradient was formed across the vesicle membrane. Vesicles loaded internally with K+ showed only 10% of the Ca2+ uptake activity observed with Na+-loaded vesicles. Dissipation of the Na+ gradient with the monovalent cation exchange ionophores nigericin or narasin caused a rapid decline in Ca2+ uptake activity. The Ca2+-ionophore A23187 inhibited Ca2+ uptake by Na+-loaded vesicles and enhanced the rate of Ca2+ loss from the vesicles after uptake. Efflux of preaccumulated Ca2+ from the vesicles was stimulated 30-fold by the presence of 50 mM Na+ in the external medium. Na+-dependent uptake and efflux of Ca2+ were both inhibited by La3+. The results indicate that cardiac membrane vesicles exhibit Na+-Ca2+ exchange activity. Fractionation of the vesicles by density gradient centrifugation revealed a close correspondence between Na+-Ca2+ exchange activity and specific ouabain-binding activity among the various fractions. This relationship suggests that the observed Na+-Ca2+ exchange activity derives from the sarcolemmal membranes within the vesicle preparation.     

Pulse labeling of small nuclear ribonucleoproteins in vivo reveals distinct patterns of antigen recognition by human autoimmune antibodies.

Antibodies directed against small nuclear ribonucleoprotein ( snRNP ) particles are found in the Sm and RNP autoimmune sera from numerous patients with systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD). These two reactivities differ in disease distribution as well as antigen specificity. Although sera from both of these autoimmune syndromes contain snRNP reactive antibodies, distinction in antigen binding specificity have been difficult to define because of the particulate nature of the snRNP antigen. To overcome this problem, while retaining the antigen in a native state, cells were pulse-labeled with [35S]methionine for 8 min to generate radioactive snRNP proteins in forms reflecting incomplete de novo particle assembly. Immunoprecipitation of snRNP antigen prepared in this manner revealed clearly distinct patterns of Sm and RNP immunorecognition . While Sm sera precipitated all eight labeled snRNP proteins, RNP antibodies precipitated only two of the eight. However, a brief pulse followed by periods of cold chase demonstrated that RNP sera can eventually coprecipitate all components of the complete particle. In addition to antibodies to the other six snRNP peptides, all Sm sera tested have been found to contain the RNP-like reactivity with snRNP proteins A and C. RNP reactivity with these two components is of particular interest because these proteins are unique in the metabolism of snRNPs. Defining and distinguishing the precise peptides recognized by Sm and RNP antibodies has helped to clarify the biochemical basis of the standard laboratory tests for these antigen reactivities.     

Phosphorylation of the DNA-binding domain of nonhistone high-mobility group I protein by cdc2 kinase: reduction of binding affinity.

Mammalian high-mobility group I nonhistone protein (HMG-I) is a DNA-binding chromatin protein that has been demonstrated both in vitro and in vivo to be localized to the A + T-rich sequences of DNA. Recently an unusual binding domain peptide, "the A.T-hook" motif, that mediates specific interaction of HMG-I with the minor groove of DNA in vitro has been described. Inspection of the A.T-hook region of the binding domain showed that it matches the consensus sequence for phosphorylation by cdc2 kinase. Here we demonstrate that HMG-I is a substrate for phosphorylation by purified mammalian cdc2 kinase in vitro. The site of phosphorylation by this enzyme is a threonine residue at the amino-terminal end of the principal binding-domain region of the protein. Labeling of mitotically blocked mouse cells with [32P]phosphate demonstrates that this same threonine residue in HMG-I is also preferentially phosphorylated in vivo. Competition binding studies show that cdc2 phosphorylation of a synthetic binding-domain peptide significantly weakens its interaction with A + T-rich DNA in vitro, and a similar weakening of DNA binding has been observed for intact murine HMG-I protein phosphorylated by the kinase in vitro. These findings indicate that cdc2 phosphorylation may significantly alter the DNA-binding properties of the HMG-I proteins. Because many cdc2 substrates are DNA-binding proteins, these results further suggest that alteration of the DNA-binding affinity of a variety of proteins is an important general component of the mechanism by which cdc2 kinase regulates cell cycle progression.     

Persistent beneficial effect of postconditioning against infarct size: role of mitochondrial K<Subscript>ATP</Subscript> channels during reperfusion

This study tested the hypothesis that inhibition of myocardial injury and modulation of mitochondrial dysfunction by postconditioning (Postcon) after 24 h of reperfusion is associated with activation of K(ATP) channels. Thirty dogs undergoing 60 min of ischemia and 24 h of reperfusion (R) were randomly divided into four groups: Control: no intervention at R; Postcon: three cycles of 30 s R alternating with 30 s re-occlusion were applied at R; 5-hydroxydecanoate (5-HD): the mitochondrial K(ATP) channel blocker was infused 5 min before Postcon; HMR1098: the sarcolemmal K(ATP) channel blocker was administered 5 min before Postcon. After 24 h of R, infarct size was smaller in Postcon relative to Control (27 +/- 4%* Vs. 39 +/- 2% of area at risk), consistent with a reduction in CK activity (66 +/- 7* Vs. 105 +/- 7 IU/g). The infarct-sparing effect of Postcon was blocked by 5-HD (48 +/- 5%(dagger)), but was not altered by HMR1098 (29 +/- 3%*), consistent with the change in CK activity (102 +/- 8(dagger) in 5-HD and 71 +/- 6* IU/g in HMR1098). In H9c2 cells exposed to 8 h hypoxia and 3 h of reoxygenation, Postcon up-regulated expression of mito-K(ATP) channel Kir6.1 protein, maintained mitochondrial membrane potential and inhibited mitochondrial permeability transition pore (mPTP) opening evidenced by preserved fluorescent TMRE and calcein staining. The protective effects were blocked by 5-HD, but not by HMR1098. These data suggest that in a clinically relevant model of ischemia-reperfusion (1) Postcon reduces infarct size and decreases CK activity after prolonged reperfusion; (2) protection by Postcon is achieved by opening mitochondrial K(ATP) channels and inhibiting mPTP opening. *P < 0.05 Vs. Control; (dagger) P < 0.05 Vs. Postcon.