William D. Gray

The anticonvulsant action of the carbonic anhydrase inhibitor methazolamide: Possible involvement of a noradrenergic mechanism

Abstract In contrast to previous concepts, the noradrenergic mechanism required for the anticonvulsant action of inhibitors of carbonic anhydrase in mice is extracerebral on the basis of the following: (1) the l-aromatic amino acid decarboxylase inhibitor Ro 4-4602/1 abolished the restorative action of d,1-dopa in reserpine- and phenoxy-benzamine-treated mice without evidence of significant inhibition of 1-aromatic amino acid decarboxylase in brain, (2) depletion of extracerebral stores of norepinehrine by the i.v. administration of 6-hydroxydopamine abolished the anticonvulsant effect of methazolamide, and (3) the anticonvulsant action of the carbonic anhydrase inhibitor in 6-hydroxydopamine-treated mice was restored by the administration of d,1-dopa. The noradrenergic mechanism appears to be of the α-type. Consistent antagonist action was shown by the α-blockers varied in action. The antagonist action of the α-blockers studied appeared to be specifically related to α-adrenergic blockade because (1) potency and duration of antagonist action correspond with potency and duration of α-adrenergic blockade, (2) phenoxybenzamine failed to antagonize the anticonvulsant action of diphenylhydantoin, (3) the anticonvulsant action of methazolamide was not abolished when phenoxybenzamine was given after the carbonic anhydrase inhibitor, (4) d,1-dopa administration reversed the antagonist action of phenoxybenzamine, and (5) the dopamine β-hydroxylase inhibitor U-14624 annulled the reversal of phenoxybenzamines antagonist action by d,1-dopa. The anticonvusant action of methazolamide in rats was not affected by depletion of cerebral or extracerebral stores of norepinephrine by 6-hydroxydopamine. Anticonvulsant action was abolished by the administration of reserpine to rats injected i.vent. with 6-hydroxydopamine. The data suggest that norepinephrine and serotonin both are involved in the anticonvulsant action of inhibitors of carbonic anhydrase in rats.

The intracellular localization of carbonic anhydrase and a carbonic anhydrase inhibitor in the brains of mice

Abstract Homogenates prepared from the perfused brains of mice were differentially centrifuged in 0.25 M sucrose. On the basis of activity per mg of nitrogen, only the supernatant showed a concentration of carbonic anhydrase activity greater than that of the original homogenate (about two- to three-fold). No concentration of activity was found in the particulate fraction, in any of its components studied, or in the washes of the various residues. Partition of per cent activity varied with the procedure used, but approximately two-thirds of the total activity of the original homogenate were in the supernatant fraction; the total particulate matter accounted for about one-third. No differences of any consequence were found amongst whole brain, cortex, and brain with the cortex removed. The data are believed to demonstrate the intracellular localization of carbonic anhydrase in the soluble fraction of cells; the activity of particulate matter is considered to be the result of contamination. The inhibitor of carbonic anhydrase found in the brains of mice following the intravenous administration of methazolamide was almost entirely localized in the supernatant fractions; an intercellular localization in the soluble fraction is also postulated. The localization of both carbonic anhydrase and carbonic anhydrase inhibitor in the soluble fraction of homogenates of the brains of mice does not constitute evidence of the inhibition of the enzyme in the brain in vivo . However, the concentrations of inhibitor found in the whole homogenates 15 min and 2 hr after the administration of doses of methazolamide at the level of the ED 95 for anticonvulsant effect were theoretically capable of causing maximum inhibition of carbonic anhydrase in the brains of mice. Anticonvulsant action and inhibition of carbonic anhydrase are probably related.

Effect of cortisone on anaphylactic response of guinea pig ileum.

Summary Treatment of guinea pigs during the period of sensitization to horse serum with 5 mg/kg of cortisone acetate daily for 20 days did not abolish the Arthus reaction or affect the level of tissue antibody as measured by the anaphylactic response of the isolated ileum. Injection of 25 mg intraperi-toneally 4 1/2 and 6 1/2 hours before sacrifice likewise had no effect. Cortisone acetate in vitro had no effect on the antigen-antibody reaction of the Arthus type. Ethyl alcohol, at a concentration of 0.8%, usually abolished the anaphylactic response. Some blockade of the antigen-antibody reaction by sodium salicylate was indicated. The histamine sensitivity of the isolated ileum was not affected by cortisone acetate treatment in vivo or in vitro.