EFFECTS ON TISSUE FUNCTIONS 501 



duction rate is slowed. It is difficult to reconcile these results with those of 

 Richter (1940), who reported that 0.92 mM p-benzoquinone has little 

 effect on the cardiac rate until the contractile amplitude has been reduced 

 15%, the pacemaker cells failing rather suddenly. It is possible that im- 

 purities in the quinone preparations might have accounted for some of the 

 actions in this early work. It is interesting that 0.09-0.9 mM p-benzoquinone 

 induces a slow development of contracture, indicating a similar effect in 

 this regard to that on skeletal muscle (Richter, 1941). 



The reports on the cardiac actions of the naphthoquinones are equally 

 discrepant. Supniewski et al. (1936) found 1,4-naphthoquinone 0.0063- 

 6.3 mM to progressively depress the amplitude of the frog heart, 12.6 mM 

 causing extrasystoles, other dysrhythmias, and a semisystolic arrest. Men- 

 adione at concentrations above 0.057 depresses the amplitude but even 

 at 11.4 mM the heart continues to beat, although at a slower rate. Phthiocol 

 at 0.0053 mM slightly augments contractility, but at 0.053~5.3mM there 

 is scarcely an effect, 10.6 mM definitely depressing the contractile ampli- 

 tude. Fromherz (1941) claimed that the frog heart can beat in a 1:1000 

 emulsion of menadione (5.7 mM) and hence is not sensitive to menadione 

 at all. The results of Cannava and Cavalleri (1948, 1949) are quite different, 

 in that they found menadione to depress the frog heart above 0.011 mM 

 and to arrest it in a few minutes at 0.28 mM. Menadiol is of similar potency 

 and 3-methylmenadione is even more potent, so that a reaction with SH 

 groups is made unlikely. The isolated rabbit heart is 2-4 times more sen- 

 sitive than the frog heart to menadione and menadiol; the results with 

 3-methylmenadione may be summarized: 0.000053-0.00053 mM slightly 

 depressant, 0.0053 mM markedly depressant with a-v dissociation, and 

 0.053 mM arresting. Menadione injected intravenously into dogs at 

 1-2 mg/kg increases the cardiac rate, depresses the t wave (which may 

 become negative) and the st segment, elevates the p wave, and disturbs 

 conduction, especially in the bundle. The coronary flow in rabbit hearts 

 is increased 25% by 0.00142 mM juglone; simultaneously there are no 

 changes in rate or contractility, so the coronary effect must result from 

 an action directly on the vessels (Auyong et al., 1962). 



Smooth Muscle 



The intestine of the rabbit responds to phthiocol by a progressive de- 

 pression of peristalsis and tonus as the concentration is raised from 0.011 

 to 5.3 mM, at which complete arrest occurs (Supniewski et al., 1936). 

 In contrast, both phthiocol and menadione injected into rabbits cause 

 increases in motility and tonus. p-Benzohydroquinone arrests isolated 

 rabbit intestine at 0.6 mM aerobically in neutral solution, but in the ab- 

 sence of oxygen even 1.2 mM is ineffective, and decreasing the pH abolishes 

 the effect, presumably due to slowing the formation of the quinone (Ther 



