Carbonic anhydrase: the middle years, 1945-1960, and introduction to pharmacology of sulfonamides

New insights into carbonic anhydrase inhibition, vasodilation, and treatment of hypertensive-related diseases

Carbonic anhydrase (CA) and its inhibitors are relevant to many physiological processes and diseases. The enzyme is differentially expressed throughout the body, in concentration and subcellular location, and as 13 catalytically active isoforms. Blood vessels contain small amounts of CA, but the enzyme's role in vascular physiology and blood pressure regulation is uncertain. However, considerable recent evidence points to vasodilation by CA inhibitors. CA inhibition in vascular smooth muscle, endothelium, heart, blood cells, and nervous system could all contribute. It is equally plausible that other targets besides CA for all known CA inhibitors may account for their vascular effects. I will review this knowledge and important remaining gaps relating to treatment of hypertensive-related diseases with potent sulfonamide inhibitors, such as acetazolamide; but also the possibility that CA inhibition by thiazides and loop diuretics, although generally weaker, may have antihypertensive effects beyond their inhibition of renal sodium transporters.

Peripheral nerve carbonic anhydrase activity and chronic acetazolamide treatment of rats

Examination of cranial nerves shows that the sensory infraorbital branch of the trigeminal nerve contains many carbonic anhydrase-reactive axons whereas axons of the motor facial nerve are non-reactive. This motor/sensory axon staining difference holds for both cranial and spinal nerves. Chronic treatment with acetazolamide produced no apparent changes in carbonic anhydrase histochemical activity or the structure of peripheral nerve fibers.

Delayed protein digestion in the alligator following carbonic anhydrase inhibition

Small alligators were injected with a carbonic anhydrase (CA) inhibitor (dichlorphenamide) and a day later they were fed large amounts of lean beef. The rate of protein digestion was determined and compared with that in controls fed the same amount. The controls began digestion at once, while in the CA-inhibited ones, digestion was blocked for over 10 hr. The inhibitor decreased gastric HCl production to one-third that in controls and delayed activation of pancreatic and intestinal proteases. After 15 hr, digestion began in the inhibited group and proceeded to completion. Once digestion began, further injections of the inhibitor could not block it. It seems that CA inhibition blocks digestion (for a time) by reducing HCl synthesis. NaHCO3 to neutralize the acid chyme in the intestine, was derived from that in the plasma.