Nonspecific endothelin-receptor antagonist blunts monocrotaline-induced pulmonary hypertension in rats

Endothelin-1 (ET-1), a potent vasoactive and mitogenic peptide, has been implicated in the pathogenesis of several forms of pulmonary hypertension. We hypothesized that nonspecific blockade of ET receptors would blunt the development of monocrotaline (MCT)-induced pulmonary hypertension in rats. A single dose of the nonspecific ET blocker bosentan (100 mg/kg) given to intact rats by gavage completely blocked the pulmonary vasoconstrictor actions of Big ET-1 and partially blunted hypoxic pulmonary vasoconstriction. After 3 wk, MCT-injected (105 mg/kg sc) rats gavaged once daily with bosentan (200 mg/kg) had lower right ventricular (RV) systolic pressure (RVSP), RV-to-body weight (RV/BW) and RV-to-left ventricular (LV) plus septal (S) weight [RV/(LV+S)] ratios and less percent medial thickness of small pulmonary arteries than control MCT-injected rats. Lower dose bosentan (100 mg/kg) had no effect on these parameters after MCT or saline injection. Bosentan raised plasma ET-1 levels but had no effect on lung ET-1 levels. Bosentan (200 mg/kg) also had no effect on wet-to-dry lung weight ratios 6 days after MCT injection. When given during the last 10 days, but not the first 11 days of a 3-wk period after MCT injection, bosentan reduced RV/(LV+S) compared with MCT-injected controls. We conclude that ET-1 contributes to the pathogenesis of MCT-induced pulmonary hypertension and acts mainly during the later inflammatory rather than the acute injury phase after injection.     

Efficient autoproteolytic processing of the MHV-A59 3C-like proteinase from the flanking hydrophobic domains requires membranes

The replicase gene of the coronavirus MHV-A59 encodes a serine-like proteinase similar to the 3C proteinases of picornaviruses. This proteinase domain is flanked on both sides by hydrophobic, potentially membrane-spanning, regions. Cell-free expression of a plasmid encoding only the 3C-like proteinase (3CLpro) resulted in the synthesis of a 29-kDa protein that was specifically recognized by an antibody directed against the carboxy-terminal region of the proteinase. A protein of identical mobility was detected in MHV-A59-infected cell lysates. In vitro expression of a plasmid encoding the 3CLpro and portions of the two flanking hydrophobic regions resulted in inefficient processing of the 29-kDa protein. However, the efficiency of this processing event was enhanced by the addition of canine pancreatic microsomes to the translation reaction, or removal of one of the flanking hydrophobic domains. Proteolysis was inhibited in the presence of N-ethylmaleimide (NEM) or by mutagenesis of the catalytic cysteine residue of the proteinase, indicating that the 3CLpro is responsible for its autoproteolytic cleavage from the flanking domains. Microsomal membranes were unable to enhance the trans processing of a precursor containing the inactive proteinase domain and both hydrophobic regions by a recombinant 3CLpro expressed from Escherichia coli. Membrane association assays demonstrated that the 29-kDa 3CLpro was present in the soluble fraction of the reticulocyte lysates, while polypeptides containing the hydrophobic domains associated with the membrane pelletes. With the help of a viral epitope tag, we identified a 22-kDa membrane-associated polypeptide as the proteolytic product containing the amino-terminal hydrophobic domain.     

Anomalies in hepatobiliary excretion of technetium-99m-MAG3 preparations

Technetium-99m-MAG3 is accepted as a renal tubular function agent. However, sporadic liver and gall bladder visualisation during its clinical use is clearly a disadvantage. HPLC-purified 99mTc-MAG3 samples exhibited appreciable hepatobiliary uptake (7%), and an elevated level of such uptake was observed in unpurified kit preparations, which was stated to be associated with the excretory property of the radiolabeled kit impurities. To verify this we attempted to quantitate the hepatobiliary uptake of the kit preparations with that of its radiolabeled components. The contribution of each component toward hepatobiliary uptake of the sample was calculated from their abundance in the chelate mixture and the individual biodistribution of the isolated components. However, the anticipated hepatobiliary uptake of different preparations of 99mTc-MAG3 calculated in this way was always lower than that of the experimental value determined directly. Further work is needed to explain the anomaly.     

Metabolic efficiency during arm and leg exercise at the same relative intensities

This study was conducted to compare gross efficiency (GE), net efficiency (NE), work efficiency (WE), and delta efficiency (DE) between arm crank and cycle exercise at the same relative intensities. Eight college-aged males underwent two experimental trials presented in a randomized counterbalanced order. During each trial subjects performed three intermittent 7-min exercise bouts separated by 10-min rest intervals on an arm or semirecumbent leg ergometer. The power outputs for the three bouts of arm crank or cycle exercise corresponded to 50, 60, and 70% of the mode-specific VO2peak. GE, NE, and WE were determined as the ratio of Kcal.min-1 equivalent of power output to Kcal.min-1 of total energy expended, energy expended above rest and energy expended above unloaded exercise, respectively. DE was determined as the ratio of the increment of Kcal.min-1 of power output above the previous lower intensity to the increment of kcal.min-1 of total energy expended above the previous lower intensity. GE and NE did not differ between arm crank and cycle exercises. However, WE was lower (P < 0.05) during arm crank than cycle exercise at 50, 60, and 70% VO2peak. DE was also lower (P < 0.05) during arm crank than cycle exercise at delta 50-60 and at delta 60-70% VO2peak. It is concluded metabolic efficiency as determined by work and delta efficiency indices was lower during arm crank compared with cycle exercise at the same relative intensities. These findings add to the understanding of the difference in metabolic efficiency between upper and lower body exercise.     

The ''no suicide contract'': helpful or harmful?

1. Contracting for Safety (CFS) has become an integral part of nursing practice but never has been subjected to scientific scrutiny. 2. Clinical reasons for avoiding the use of contracting with some patient populations exist, including that some patients may construe CFS as a failure of empathy by the caregiver. 3. CFS can, in some instances, be helpful in establishing a therapeutic relationship or aiding in assessment, but never should be the sole basis for determining a patient's lethality.     

Response of mouse plantaris muscle to functional overload: comparison with rat and cat

Functional overload (FO) of a muscle by removing its synergists results in a compensatory hypertrophy of the muscle. However, the extent of the response appears to be dependent, at least in part, on the activity and/or loading levels of the muscle following surgery. Thus, differences in the inherent physical activity levels across species may be an important factor to consider. In the present study, the effects of 8 weeks of FO on the isometric mechanical properties of the plantaris of mice (highly active) were determined and the findings compared with the results from previous studies performed on the plantaris of rats (highly active) and cats (less active). FO resulted in approximately a doubling of the mass, the physiological cross-sectional area and the maximum tetanic tension per unit cross-sectional area, was similar in the plantaris of control and FO mice. Isometric twitch speed properties were unaffected, but the tension enhancement in response to an increase in the rate of stimulation showed the pattern of a "faster" muscle following FO. The fatigue resistance of the plantaris in FO mice was significantly higher than in control mice. Although the degree of hypertrophy that occurred in the mouse plantaris was similar to that observed after FO in rats and in cats that are exercised intermittently at high intensities, there were differences in the mechanical properties that may be related to the adaptability of species and/or the behavioral responses to the overload.