Experimental physiology
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Experimental physiology · Jan 1997
Effects of nitric oxide on diaphragmatic muscle endurance and strength in pigs.
The aim of the study was to evaluate the effects of nitric oxide (NO) on diaphragmatic fatigue in fifteen anaesthetized, mechanically ventilated pigs, divided into three groups. The animals were pre-treated with indomethacin (3 mg kg-1, i.v.) to block the cyclo-oxygenase pathway. To group 1 pigs (n = 6) NG-nitro-L-arginine methyl ester (L-NAME, 5 mg kg-1 i.v.) was administered as a bolus to block endogenous NO production, while group 2 pigs (n = 6) were infused with sodium nitroprusside (SNP, 0.023 mg kg-1, i.v.), a donor of NO. ⋯ However, both L-NAME and SNP caused significant decreases in diaphragmatic endurance capacity. The fatigue appearing after L-NAME is probably correlated with a decline in diaphragmatic blood flow, as evidenced by the increase in SVR and the decrease in CO, and consequently in oxygen supply. In contrast, the decrease in endurance capacity after SNP infusion can be attributed to a direct action of NO on skeletal muscle.
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Experimental physiology · Jul 1996
Separation of the components of the delayed rectifier potassium current using selective blockers of IKr and IKs in guinea-pig isolated ventricular myocytes.
Delayed rectifier potassium current (IK) was investigated in guinea-pig isolated ventricular myocytes under voltage-clamp conditions ('switched' single electrode clamp), using selective blockers and/or different activation protocols to separate its rapid (IKr) and slow (IKs) components. The class III antiarrhythmic compound E4031 (5 microM) was used to block IKr and the anaesthetic drugs propofol (100 microM) or thiopentone (100 microM) to block IKs. In all experiments L-type calcium currents were blocked with nifedipine (2 microM). ⋯ Forskolin (1 microM) enhanced the current most consistent with IKs. Propofol (300 microM) caused a 64 +/- 3% increase in action potential duration in the presence of both E4031 (5 microM) and nifedipine (2 microM), consistent with an important role for IKs in the repolarization of the action potential in the guinea-pig heart. The observations therefore provide further support for separate components of IK with different characteristics in the guinea-pig heart; it appears that E4031 and propofol or thiopentone are useful complementary tools for their separation.
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Experimental physiology · Nov 1994
Defensive reflexes of the respiratory system in anaesthetized rabbits during high frequency jet ventilation.
The defensive airway reflexes during high frequency jet ventilation (HFJV) were studied in anaesthetized, non-vagotomized (n = 16) and vagotomized (n = 11) rabbits. The animals were ventilated by a high frequency jet ventilator. Sneezing and coughing were evoked by mechanical stimulation of the airways. ⋯ This inhibition occurred not only in defensive reflexes evoked from the regions with increased pressure (trachea, bronchi), but also from the nose. Vagotomy diminished but did not fully eliminate the changes in sneezing accompanying HFJV. The intensity of maximum expiratory efforts was not significantly affected by HFJV in both subgroups.
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Experimental physiology · Sep 1994
Comparative StudyInteraction of aldosterone and oxytocin to influence renal sodium excretion in rats.
The possibility of an interaction between oxytocin and aldosterone to influence renal Na+ excretion was investigated in Inactin-anaesthetized male Sprague-Dawley rats. Endogenous plasma concentrations of aldosterone were suppressed by either adrenalectomy or bicarbonate infusion. The effects of 2 h intravenous administration of oxytocin (0.04 pmol/min) and/or aldosterone (42 pmol/min) on renal Na+ handling were studied in 0.077 M NaCl-infused adrenalectomized (Adx) rats and groups of intact animals that were infused with 0.077 M NaHCO3. ⋯ However, combined administration of aldosterone and oxytocin was associated with a significantly (P < 0.01) increased Na+ excretion rate from a peak pretreatment value of 6.8 +/- 0.7 mumol/min to a peak value of 11.5 +/- 1.1 mumol/min by 1 h 40 min after the start of treatment in Adx rats (n = 7). In bicarbonate-infused rats (n = 8) Na+ excretion rose within 20 min of the start of treatment from a pretreatment peak of 9.0 +/- 0.8 mumol/min to a peak value of 13.5 +/- 0.8 mumol/min in response to combined hormone administration. In conclusion, we have shown that concomitant administration of aldosterone and oxytocin increased the rate of excretion of Na+ in two different preparations, which supports the idea of an interaction between the steroid and oxytocin to promote Na+ loss.
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Experimental physiology · Mar 1992
Modulation by peripheral conditioning stimuli of the responses of trigeminal brain stem neurones and of the jaw opening reflex to tooth pulp stimulation in chronically prepared, anaesthetized cats.
The effects of peripheral conditioning stimuli on the thresholds of the jaw opening reflex (JOR) and of trigeminal brain stem neurones to tooth pulp stimulation were examined in chronically prepared, anaesthetized cats. High intensity electrical conditioning stimuli applied to the ipsilateral forepaw produced an increase in the thresholds of both responses, with the JOR thresholds being elevated significantly more, and remaining elevated for significantly longer, than those of the neurones. These findings suggest that the elevation of the JOR cannot be explained just by inhibitory effects on the brain stem neurones.