Hemodynamic and metabolic responses to self-paced and ramp-graded exercise testing protocols

Recent examinations have shown lower maximal oxygen consumption during traditional ramp (RAMP) compared with self-paced (SPV) graded exercise testing (GXT) attributed to differences in cardiac output. The current study examined the differences in hemodynamic and metabolic responses between RAMP and SPV during treadmill exercise. Sixteen recreationally trained men (aged23.7 ± 3.0 years) completed 2 separate treadmill GXT protocols. SPV consisted of five 2-min stages (10 min total) of increasing speed clamped by the Borg RPE6-20 scale. RAMP increased speed by 0.16 km/h every 15 s until volitional exhaustion. All testing was performed at 3% incline. Oxygen consumption was measured via indirect calorimetry; hemodynamic function was measured via thoracic impedance and blood lactate (BLa^-) was measured via portable lactate analyzer. Differences between SPV and RAMP protocols were analyzed as group means by using paired-samples t tests (R Core Team 2017). Maximal values for SPV and RAMP were similar (p > 0.05) for oxygen uptake (47.1 ± 3.4 vs. 47.4 ± 3.4 mL·kg^-1·min^-1), heart rate (198 ± 5 vs. 200 ± 6 beats·min^-1), ventilation (158.8 ± 20.7 vs. 159.3 ± 19.0 L·min^-1), cardiac output (26.9 ± 5.5 vs. 27.9 ± 4.2 L·min^-1), stroke volume (SV) (145.9 ± 29.2 vs. 149.8 ± 25.3 mL·beat^-1), arteriovenous oxygen difference (18.5 ± 3.1 vs. 19.7 ± 3.1 mL·dL^-1), ventilatory threshold (VT) (78.2 ± 7.2 vs. 79.0% ± 7.6%), and peak BLa^- (11.7 ± 2.3 vs. 11.5 ± 2.4 mmol·L^-1), respectively. In conclusion, SPV elicits similar maximal hemodynamic responses in comparison to RAMP; however, SV kinetics exhibited unique characteristics based on protocol. These results support SPV as a feasible GXT protocol to identify useful fitness parameters (maximal oxygen uptake, oxygen uptake kinetics, and VT).

Development of a generalized, quantitative physicochemical model of CYP3A4 inhibition for use in early drug discovery

PURPOSE

To examine the structure-activity relationships for the inhibition of the activity of recombinant human CYP3A4 and to establish a generalized, quantitative physicochemical model for use in early drug discovery.

METHODS

Inhibition of the activity of recombinant human CYP3A4 (erythromycin N-demethylase) by 30 diverse chemicals was studied using enhanced throughput methodology.

RESULTS

There was a general, strong correlation between the IC50 value determined against erythromycin N-demethylase activity and lipophilicity (LogD7.4) (r2 = 0.68, p <0.0001). This relationship was strengthened further by subdividing the structures studied into two distinct subpopulations of chemistry within the dataset. These could be identified by the absence (r2 = 0.80, p <0.0001) or presence (r2 = 0.69, p <0.0001) of a sterically uninhindered N-containing heterocycle, more specifically a pyridine, imidazole, of triazole function. The presence of these structural motifs increased the potency of CYP3A4 inhibition by approximately 10-fold for a given lipophilicity (LogD7.4.value). More detailed analyses of AstraZeneca compounds demonstrated that the inhibitory potency of the pyridine structure can be attenuated through direct steric effects or electronic substitution resulting in a modulation of the pKa of the pyridine nitrogen, thereby influencing its ability to interact with the CYP heme.

CONCLUSIONS

A generalized, quantitative model is proposed for the inhibition of the major drug metabolizing enzyme, CYP3A4. This model indicates the importance of lipophilicity and rationalizes increased potency arising through additional interactions with the heme iron. These general relationships were shown to be applicable to a selection of compounds of interest to several early research projects.

Laboratory infection of primates with Ascaris suum to provide a model of allergic bronchoconstriction

Wild-caught non-human primates are naturally sensitive to Ascaris antigen and provide a useful model for studying atopic asthma. The present study was carried out to determine the effect of experimentally infecting home-bred macaques with the nematode Ascaris suum and hence provide an alternative for the naturally occurring model. Following oral infection with the parasite the animals developed a blood eosinophilia and specific antibodies to purified Ascaris antigen. These antibodies appeared to be of the IgE class as they could be detected by a radiometric assay using a radiolabelled antibody to human IgE. However, on further investigation, using the passive cutaneous anaphylaxis test, two classes of antibody were found, a heat labile (56 degrees C) and a heat stable antibody. Lung lavage cells taken from monkeys infected with Ascaris suum were shown to include cells morphologically characteristic of mast cells and released histamine when challenged in vitro with Ascaris antigen. Hence this model of immediate hypersensitivity provides a simple alternative to the less accessible natural model.

Rat eosinophil-mediated antibody-dependent cellular cytotoxicity: investigations of the mechanisms of target cell lysis and inhibition by glucocorticoids

Purified eosinophils from the peritoneal washings of N. brasiliensis infected rats demonstrated antibody-dependent cellular cytotoxicity (ADCC) for 51Cr-labelled chicken erythrocytes. The F(ab')2 fragment of the antibody did not support cytotoxicity thereby demonstrating the importance of the eosinophil Fc receptor to this activity. Bystander lysis of erythrocytes did not occur, indicating that the eosinophil does not release lytic agents free into the medium. Cytochalasin B (1.25-5 micrograms/ml) colchicine (10(-5)-10(-3) M) and chloroquine (10(-4)-10(-3) M) inhibited eosinophil ADCC. Inhibition was also demonstrated by methylprednisolone, 10(-7)-10(-3) M and this inhibition was blocked by the protein synthesis inhibitor, cycloheximide (25 micrograms/ml). Cycloheximide alone had no effect. This block of steroid inhibition by cycloheximide suggests that the steroid effect on this system may be mediated by a newly synthesized protein and implies that the eosinophil may possess a glucocorticoid receptor.

Anaphylactic bronchoconstriction in rats immunized with antigen-coated latex particles

Studies have been carried out on the immunization of rats with antigen-coated latex particles. These studies confirmed that a significant lung blood eosinophilia is induced by a repeat intravenous injection of antigen-coated latex particles. Rats treated with antigen-coated latex particles also become sensitive to antigen such that on antigen challenge the animals show bronchoconstriction. Studies show that the bronchoconstriction is specific for antigen, but is unlikely to be mediated by tissue-fixing antibodies. Experiments comparing different immunization schedules involving latex particles indicate a strong association between the level of eosinophilia and degree of antigen-induced bronchoconstriction. These studies suggest that eosinophils may contribute to the anaphylactic bronchoconstriction.