The distribution and movements of carbon dioxide, carbonic acid and bicarbonate between blood and milk in the goat.

Abstract

1. A–V differences and milk concentrations of respiratory gases, pH, HCO3 and H2CO3 have been measured in lactating goats and cows. 2. The pH and [HCO3 minus] of milk were significantly lower than those of plasma while milk PCO2 was virtually identical to that of mammary venous blood. [H2CO3+ dissolved CO2] was similar in milk and blood. 3. 14‐C (from injected [14‐C]HCO3 minus was found to cross the mammary epithelium in both directions. 14‐C also passed across the duct epithelium and since this epithelium has previously been shown to be impermeable to ions it is argued that 14‐C crossed in an unionized form, i.e. as CO2 and/or H2CO3. 4. Hourly milking with the aid of oxytocin raised milk pH, [HCO3 minus], [H2CO3], [Na] and E1Cl], and lowered [K], [lactose] and [phosphate]. These effects are discussed in relation to the hypothesis proposed previously for the action of oxytocin on milk composition. 5. A scheme for the distribution and movements of CO2, H2CO3 and HCO3 minus between extracellular fluid and milk is suggested, and discussed in relation to Cl minus transport. © 1975 The Physiological Society