Alan H. Goldberg

Effects of halothane on isometric contractions of isolated heart muscle.

In isometric contractions of an isolated heart muscle preparation exposed to halothane (0.10, 0.40, 0.85, 1.05 and 2.35 volumes per cent), peak developed tension and maximum rate of tension development were reduced as much as 53 per cent and 57 per cent, respectively, in direct proportion to the concentration of the anesthetic. Time to peak tension and total twitch duration were not decreased more than 6.3 per cent by any concentration of halothane. Resting tension was affected only by the highest concentration, 2.35 volumes per cent, which lowered it 6.8 per cent Relaxation time and muscle length were not altered. Recovery from the effect of halothane was essentially complete in each instance. The results are consistent with the concept that halothane exerts its cardiac effects primarily by a direct reduction in active state intensity of heart muscle.

Direct myocardial effects of nitrous oxide.

Eight isometrically contracting rat left ventricular trabeculae carneae muscle preparations were exposed to concentrations of 25, 50, and 75 vol per cent of both N2O and N2 Both gases depressed peak developed isometric tension and the maximum rates of tension development and relaxation in relation to the gas concentrations. In five other muscles, paired electrical stimulation reversed the negative inotropic effects of N2O and N2 The relative potentiation of contractility achieved with paired stimulation was the same in the presence of O2 N2O, and N2 Since N2O did not produce any additional depressant effects over and above those observed with N2, and since the positive inotropic effects of paired stimulation were unchanged by this anesthetic, it was concluded that N2O does not possess any direct myocardial depressant or stimulant properties.

Depression of myofibrillar ATPase activity by halothane.

Halothane was found to reduce the ATPase activity of both myocardial and skeletal muscle myofibrillar preparations. The results support the hypotheses that there is a close association between myocardial tension development and the enzymatic hydrolysis of ATP, and that halothane exerts its cardiac effects by inhibiting this process.

Halothane and isometric contractions of isolated pregnant rat myometrium.

The effects of halothane on isometric contractions of isolated pregnant uterine muscle strips were evaluated in tissue obtained from 13 midpregnant rats. Peak developed tension was depressed in a doserelated manner at halothane concentrations above 0.8 vol per cent, but was not affected at lower halothane concentrations. Time to peak tension was reduced 10–20 per cent, and relaxation time, 10 per cent, by halothane concentrations ranging up to 2.2 per cent. Total resting tension consisted of a passive component and a calcium-dependent component. In concentrations above 0.8 per cent, halothane rapidly removed 100 per cent of the calcium-dependent resting tension. At lower concentrations, halothane reduced it 50 per cent. The passive component of resting tension was unaffected by halothane. These actions of halothane can prevent postpartum hemostasis. They occur even with very low anesthetic concentrations and can be detected soon after introduction of anesthetic into the muscle bath. This indicates that the hemostatic hazards associated with the use of halothane for delivery may not be prevented by limiting the concentration of halothane or the duration of anesthetic exposure.

Influence of acute hypoxia on Z-line width of cardiac muscle.

Abstract Isolated guinea pig papillary muscles were exposed to 30 min of acute hypoxia. The preparations were then fixed for electron microscopy. The width of 435 control and 386 hypoxic Z-lines were measured. No statistical difference occurred between the two groups. We conclude, contrary to a recent report, that 30 min of acute hypoxia does not alter the Z-line width in heart muscle.

Does tenotomy of skeletal muscle alter Z-line width in older animals?

Results of unilateral achilles tenotomy on older (350–410 g) male rats, showed that the general width of Z-lines in the tenotomized muscles was not significantly altered by this procedure. Streaming of the Z-lines and rod formations was still present, as in younger rats.

Repositioning of fast and slow skeletal muscle

SummaryThe origins of the rat fast plantaris and slow soleus muscles were surgically reversed and their fibre types and contractile properties examinedin vitro up to 12 weeks post surgery. Muscles in which the origins had been severed and then immediately sutured back in place served as one control group. Unoperated animals served as a second control group. As compared to these groups, no significant differences in the histochemical or mechanical properties of the repositioned muscles were detected. Under the conditions of the experiments, no evidence was obtained to indicate that the intrinsic properties of a muscle could be altered by changing its site of origin and thus its functional environment.

Contractile properties of fast muscle preparations regenerating in slow muscle beds

Mechanical evidence is presented to show that fast muscle tissue regenerating in the bed of a slow muscle, and innervated by the slow muscle nerve, has contractile properties identical to those of a slow muscle regenerating in its own bed. The results do not support the idea that regenerating fast muscles are partially resistant to the transforming effects of a slow nerve.

Fluroxene and Isolated Heart Muscle

The direct myocardial effects of fluroxene were examined in isometrically and isotonically contracting isolated rat heart muscle. MAC, the minimum anesthetic concentration needed to prevent movement in response to tail clamping, was found to be 5.0 vol per cent fluroxene in the rat. At 4.6 vol per cent fluroxene, peak developed isometric tension and maximum rate of tension development were decreased 29 and 24 per cent, respectively. At 11 vol per cent, the depressions were 39 and 33 per cent. At 26.4 vol per cent, the depressions were around 60 per cent. Vmax (the maximum shortening velocity of unloaded muscle) of the force-velocity relation was unaltered by fluroxene concentrations of 0.8, 4.6, and 11 vol per cent. Even at 26.4 vol per cent, the depression in Vmax was only 25 per cent. Po (the maximum force at zero velocity), work, and power were lowered much more, with reductions ranging from 15 to 27 per cent at 4.6 vol per cent, from 40 to 42 per cent at 11.0 vol per cent, and from 65 to 69 per cent at the 26.4 vol per cent. Series elastic extension was unchanged at 0.8 and 4.6 vol per cent fluroxene, but was decreased 16 per cent at 11.0 vol per cent and 46 per cent at 26.4 vol per cent fluroxene. The data indicate the fluroxene has a direct negative inotropic effect that is associated with increased series elastic stiffness, but does not involve Vmax of the force-velocity relation until quite high anesthestic concentrations are reached. Comparative studies were also carried out with halothane. MAC for halothane in the rat was 1.0 vol per cent. The relative potency of halothane compared with fluroxene in depression of Vmax was 13.2, and its relative potency in depression of Po, 4.0.