Reduced orthostatic tolerance following 4 h head-down tilt

The cardiovascular responses to a 10-min 1.22 rad (70 degrees) head-up tilt orthostatic tolerance test (OST) was observed in eight healthy men following each of a 5-min supine baseline (control), 4 h of 0.1 rad (6 degrees) head-down tilt (HDT), or 4 h 0.52 rad (30 degrees) head-up tilt (HUT). An important clinical observation was presyncopal symptoms in six of eight subjects following 4 h HDT, but in no subjects following 4 h HUT. Immediately prior to the OST, there were no differences in heart rate, stroke volume, cardiac output, mean arterial pressure and total peripheral resistance for HDT and HUT. However, stroke volume and cardiac output were greater for the control group. Mean arterial pressure for the control group was less than HDT but not HUT. Over the full 10-min period of OST, the mean arterial pressure was not different between groups. Heart rate increased to the same level for all three treatments. Stroke volume decreased across the full time period for control and HDT, but only at 3 and 9 min for HUT. There was a higher total peripheral resistance in the HDT group than control or HUT. The pre-ejection period to left ventricular ejection time ratio was less in HDT than for control or HUT groups. These data indicate a rapid adaptation of the cardiovascular system to 4 h HDT that appears to be inappropriate on reapplication of a head to foot gravity vector. We speculate that the cause of the impaired orthostatic tolerance is decreased tone in venous capacitance vessels so that venous return is inadequate.     

Systolic pressure gradients between the wall of the left ventricle, the left ventricular chamber, and the aorta during positive inotropic states: implications for left ventricular efficiency

To study systolic pressure gradients developed between the left ventricular wall, its chamber, and the aortic root, in one group of dogs left ventricle ventral wall intramyocardial pressure, left ventricular outflow tract pressure, and aorta pressure were compared with aortic flow as well as left ventricular dimension changes during control conditions as well as during positive intropic states induced by isoproterenol, stellate ganglion stimulation, and noradrenaline. In another group of dogs systolic pressures in the ventral wall of the left ventricle, the main portion of the left ventricular chamber, and the aorta were compared with aortic flow during similar interventions, before and after the administration of phentolamine. Pressure gradients between the wall of the left ventricle and the outflow tract of the left ventricle were minimal during control states, but during the three positive inotropic states were increased significantly. In contrast, pressure gradients between the outflow tract of the left ventricle and the aortic root were insignificant during positive inotropic states; those between the wall and main portion of the chamber were only significantly different during left stellate ganglion stimulation. The data derived from these experiments indicate that useful peak power output of the left ventricle (systolic aortic pressure X flow) is unchanged following isoproterenol infusion, but is increased by stellate ganglion stimulation and noradrenaline. The useful peak power output index (an index of left ventricular efficiency derived by dividing useful peak power output by peak intramyocardial pressure) was reduced more by isoproterenol than the other two interventions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Establishment and characterization of murine macrophage hybrids

Proteose peptone-induced peritoneal macrophages from CBA/J (H-2k) mice have been fused to a hypoxanthine phosphoribosyltransferase-negative variant of the P388D1 (H-2d) murine macrophage cell line. Six hybrid clones were isolated following HAT selection and further characterized. Five of the six clones express class I antigens of both parental haplotypes by microelisa and by flow cytometric analysis. Class II antigen expression of both haplotypes was apparent following a 72-hr incubation of the hybrids with concanavalin A-stimulated rat spleen cell supernatant. However, I-Ad was expressed in all hybrids to a greater extent than I-Ak. Three clones with the highest level of I-Ak expression, E5, C2, and C4, were capable of antigen presentation to the I-Ak-restricted T-cell line, D10.G4.1. LPS induction of the hybrids resulted in a 2- to 15-fold increase in the amount of IL-1 produced relative to the P388D1 parent. Finally, in distinction to P388D1, all hybrids demonstrated increased Fc-mediated erythrophagocytosis of chromium-labeled antibody-coated erythrocytes. These murine macrophage hybrids appear stable and should serve as useful models in understanding the regulation of macrophage function.     

Resting cortisol levels and the emergence of dominant status among male vervet monkeys

Resting serum cortisol was measured in adult male vervet monkeys (Cercopithicus aethiops sabaeus) in four different conditions: (1) among groups with unaltered group membership and established dominance hierarchies; (2) among groups from which the original dominant male had been removed and in which the remaining males competed for dominant status; (3) among newly formed groups of three unfamiliar males each of which had been the dominant male in his previous group; and (4) among groups from which a dominant male was temporarily separated and returned. In Condition 1, cortisol concentrations did not differ between dominant and subordinate males. The second condition showed that cortisol levels were highest among males who eventually emerged as the dominant male. In the third condition, however, cortisol levels did not differentiate eventually dominant from eventually subordinate males. In the last condition, cortisol levels were highest in the animals that became or remained dominant following reintroduction. These data indicate that cortisol concentration does not differ between dominant and subordinate males in stable groups and that cortisol rises during competition for dominance among familiar males.     

Properties of in vitro recombinant derivatives of pJV1, a multi-copy plasmid from Streptomyces phaeochromogenes

The 10.8 kb plasmid pJV1, isolated from Streptomyces phaeochromogenes, has a high copy number (about 150) and a broad host range among Streptomyces spp. Several pJV1 derivatives carrying the thiostrepton resistance gene (tsr) of S. azureus were made. One derivative, pWOR191, was shown to promote its own transfer and to mobilize chromosomal markers in S. lividans. Another derivative, pWOR109, was non-transmissible. Deletion in vitro of a segment of pWOR109 gave pWOR120 (5.6 kb), which has single BamHI and Bg/II sites shown to be capable of accepting 'foreign' DNA such as a previously cloned S. antibioticus DNA fragment encoding tyrosinase, giving vectors (pWOR125, pWOR126) with properties resembling the well-established multicopy vector pIJ702. Shuttle vectors capable of functioning in both S. lividans and Escherichia coli were also constructed. The region of pJV1 essential for replication and maintenance was localized to a 2.5 kb segment. Stable maintenance of pWOR109 and pWOR120 was observed in the presence of derivatives of pIJ101, the progenitor of pIJ702.     

13C NMR spectroscopy of Methanobacterium thermoautotrophicum. Carbon fluxes and primary metabolic pathways

The flux of 13C-labeled carbons from the soluble metabolite 2,3-cyclopyrophosphoglycerate (CPP), a novel compound found in high concentrations exclusively in methanobacteria and methanobrevibacter, into carbohydrate-containing material has been deduced by solid-state 13C NMR spectroscopy which strongly argues for a role in gluconeogenesis for this unique metabolite. The turnover rates, but not the steady-state levels, of CPP labeled by 13CO2 or [13C]acetate depend dramatically on cell growth conditions. When the demand for carbohydrate synthesis is reduced (i.e. in stationary phase), the rates of CPP biosynthesis and degradation decrease 10-fold, and the disaccharide alpha, alpha-trehalose accumulates. Valinomycin, a metabolic inhibitor of Methanobacterium thermoautotrophicum growth, does not affect steady-state levels of CPP, but does decrease 13C uptake into the CPP pool. The effects of these different conditions on CPP labeling suggest stringent regulation of CPP linked to cellular metabolism. Labeling of CPP by [6-(13)C]glucose, which does not serve as an energy or carbon source for this organism, provides strong evidence that glucose is cleaved by the reverse of the gluconeogenesis pathway. This metabolic pathway linking glucose with triose phosphate type precursors and an analysis of the 13C NMR spectrum of CPP labeled by incubating cells with [U-13C]glucose have established that in vivo phosphoenolpyruvate synthetase must be reversible.     

Type C Niemann-Pick disease. Abnormal metabolism of low density lipoprotein in homozygous and heterozygous fibroblasts

The esterification of cholesterol derived from human low density lipoprotein (LDL) or fetal bovine serum (FBS) was deficient in cultured fibroblasts from subjects with heterozygous and homozygous type C Niemann-Pick (NPC) disease. Failure to significantly esterify LDL-derived cholesterol resulted in abnormal accumulation of predominantly unesterified cholesterol in homozygous NPC fibroblasts. Compared with normal and homozygous fibroblasts, heterozygous NPC fibroblasts synthesized intermediate levels of cholesteryl ester during the initial 6 h of incubation with LDL. The rate of cholesterol esterification in heterozygous cells was normal when measured over a 24-h period of incubation with LDL. In addition to demonstrating a defect in cholesterol esterification, homozygous NPC fibroblasts accumulated more total cholesterol when incubated with LDL or FBS than normal fibroblasts accumulated. When heterozygous NPC fibroblasts were incubated with LDL or FBS, cellular accumulation of cholesterol reached levels that were high-normal or intermediary between levels observed in normal and homozygous NPC fibroblasts. The partial expression of these metabolic errors in the heterozygous genotype relevantly links these errors to the primary mutation of this disorder.     

Comparison of material properties in fascicle-bone units from human patellar tendon and knee ligaments

The fascicle material properties in bone-fascicle-bone units were determined for the anterior and posterior cruciate ligaments (ACL, PCL), the lateral collateral ligament (LCL) and the patellar tendon (PT) from three young human donor knees. Groups of fascicles from each tissue were isolated with intact bone ends and failed at a high strain rate in a saline bath at 37 degrees C. In each knee tested the load related material properties (linear modulus, maximum stress and energy density to maximum stress) for the patellar tendon were significantly larger than corresponding values for the cruciate and collateral ligaments. Bundles from different ligaments in the same knee were similar to each other in their mechanical behavior. In addition, no significant differences were present in the maximum strains recorded for any of the four tissue types examined. The results presented have implications in studies of ligament injury. They are also important in the design and use of synthetic and biological ligament replacements and in tissue and whole knee modeling.     

Microheterogeneity of Micro tubule-Associated τ Proteins Is Due to Differences in Phosphorylation

We have studied the heterogeneity of the microtubule-associated tau proteins using tau-specific antibodies and two-dimensional electrophoresis. Both monoclonal and polyclonal antibodies to tau proteins recognize five bands in cow brain microtubule proteins run on sodium dodecyl sulfate (SDS)-polyacrylamide gels, with apparent molecular weights between 56,000 and 66,000. Immunoblots of cow brain microtubules separated on two-dimensional gels, using nonequilibrium pH gradient electrophoresis in the first dimension and SDS-gel electrophoresis in the second, reveal that greater than 30 isoforms of tau exist. The tau proteins vary in pI from 6.5 to 8.5, with the higher-molecular-weight forms being more acidic. The microheterogeneity of tau is not induced by cycling of microtubules, because two-dimensional immunoblots of tau from total brain are almost identical to those of tau from cycled tubules. Adult rat brain tau, which appears as three doublet bands on SDS gels, also exhibits considerable isoelectric heterogeneity, as does tau from 7-day-old rats, which appears as only one band on SDS gels. After dephosphorylation of cow brain tau with alkaline phosphatase, the highest-molecular-weight band disappears on SDS gels. On two-dimensional gels, the number of tau variants decreases by more than half after dephosphorylation, and the more basic species increase greatly in intensity. Preliminary experiments with tau labeled in vivo with 32PO4 also indicate that the more acidic tau proteins are the more highly phosphorylated forms. Thus, isoelectric heterogeneity of tau proteins exists at all ages and is due, at least in part to differences in the state of phosphorylation of tau isoforms.