EFFECTS ON TISSUE FUNCTIONS 503 



amine receptor sites, possibly because of a structural similarity of the qui- 

 nones to the catecholamines. 2?-Benzoquinone antagonizes the actions of 

 epinephrine on the mouse uterus, rabbit intestine and heart, the ear vessels, 

 and the toad heart, but the hydroquinone does not (Terai, 1934 a). The 

 effects of epinephrine on the frog pupil (Terai, 1934 b) and blood pressure 

 (Okagawa et al., 1934) are blocked by p-benzoquinone, and the hydroquinone 

 actually restores the response; this was interpreted as a direct oxidation of 

 the ring hydroxyls of epinephrine. p-Benzohydroquinone and catechol 

 injected intravenously at a dose of 20 mg/kg in the cat produce a sensiti- 

 zation of the nictitating membrane to epinephrine or nerve stimulation, 

 this being attributed to a retardation of epinephrine oxidation (Bacq, 

 1935). On the other hand, menadione or menadiol does not alter the blood 

 pressure response to epinephrine (Cannava, 1948 a). In the light of the re- 

 cent advances in our knowledge of the catecholamines, a reinvestigation 

 of the effects of the quinones might be worthwhile. 



Active Transport in Various Tissues 



Mann and Mann (1939) studied several inhibitors with the object of 

 finding a substance, which would more or less specifically inhibit gastric 

 acid secretion without toxic effects, for the treatment of peptic ulcer. 

 Solutions of p-benzoquinone were placed in the stomach or in Heidenhain 

 pouches and the acid secretion was determined. A concentration of 0.92 mM 

 reduces acid secretion about 50% and is not irritating, while a concentra- 

 tion of 9.2 mM inhibits secretion completely for 24 hr but produces some 

 hemorrhage. No effect was seen with 91 mM p-benzohydroquinone or re- 

 sorcinol, again demonstrating the activity of the quinone form, and pos- 

 sibly indicating in view of the work of Davenport on SH reagents that the 

 action is due to the inactivation of some unknown thiol. It may also be noted 

 that acid secretion in isolated rat stomachs is markedly depressed by 2 mM 

 tetramethyl-p-phenylenediamine, which may act in the quinonoid diimine 

 form (Patterson and Stetten, 1949). 



Incubation of rabbit kidney slices at 0*^ in 0.154 M NaCl leads to an up- 

 take of water and Na+, and a loss of K+. The presence of p-benzoquinone 

 at 0.5-2 mM accelerates these changes and this effect is partially reversible 

 (Kleinzeller and Cort, 1957). One cannot say whether the action is on active 

 transport systems or is a simple increase in permeability. The respiratory 

 increase upon adding Na+ to dog kidney slices is not affected by p-benzo- 

 quinone at 0.1 mM, although the normal respiration is inhibited some 12% 

 (Ullrich, 1958). This would be very indirect evidence that the quinone 

 probably does not interfere with Na+ transport. Interesting results on the 

 effects of analogs of coenzyme Q on Na+ transport have been obtained by 

 Weinstein and Kessler (1962, 1963). The unilateral injection of Qq, 6-Br-Qo, 

 and 6-Cl-Qo into one renal artery leads to a unilateral natriuresis. No effect 



