Carbonic Anhydrase, Diuretics and Egg Shell Formation

SINCE the work of Benesch et al. (1944) and Gutowska and Mitchell (1945) it has been generally assumed that the enzyme carbonic anhydrase plays an important role in egg shell formation by supplying the carbonate anion of calcium carbonate through the reaction CO2 + H2O⇄ H2CO3. This assumption is based on (a) the significantly greater carbonic anhydrase activity of uterine epithelium as compared with other oviduct tissue (Common, 1941), and (b) the reduction of shell deposition after feeding sulfanilamide, described by Benesch et al. (1944) and Gutowska and Mitchell (1945). Sulfanilamide and other unsubstituted sulfonamides, such as acetazolamide, are carbonic anhydrase inhibitors. As such they interfere with the reabsorption of bicarbonate in the kidney and, through the concomitant metabolic acidosis, often cause diuresis (Burger, 1960). It is therefor possible that sulfanilamide and other carbonic anhydrase inhibitors interfere with shell deposition by causing diuresis and not by limiting the supply of …