LOCALIZATION OF CARBONIC-ANHYDRASE IN THE GOAT MAMMARY-GLAND DURING INVOLUTION AND LACTOGENESIS

The aim of this study was to determine whether carbonic anhydrase (CA) activity in goat mammary capillaries is regulated mainly by local or systemic mechanisms. One gland was dried before the contralateral glan d, and after parturition only one gland was milked. Biopsies were take n from the mammary glands of three goats at 14 d intervals during invo lution and the start of the following lactation. A histochemical metho d was used to visualize sites of CA activity. To follow the involution process, milk (liquid) samples were taken from both teats each week a nd analysed for pH and composition. The time course of CA activity dis appearance and reappearance in the capillaries was related to changes in milk composition and alveolar area. A dense network of capillaries showing membrane-bound staining for CA was found surrounding the alveo li in the lactating gland. CA activity gradually decreased in the dryi ng gland, although the other gland was being milked. After 8 weeks inv olution the dried gland had a significantly lower number of stained ca pillaries than the milked gland. Almost no stained capillaries were fo und during late pregnancy, when both glands were dried and the tissue growth maximal. During lactation milk. pH was 6.6 +/- 0.3 and this inc reased to 7.0 +/- 0.1. in the course of involution. In the last trimes ter of pregnancy the pH returned to its lower value, while the mammary gland was devoid of stained capillaries. Therefore, the capillary CA could not have been directly involved in the pH regulation of milk. Th e CA activity reappeared in the capillaries directly after delivery, b ut only in the milked gland. Clearly the regulation of CA activity is influenced more by local than by systemic factors and is associated wi th the metabolic activity of milk secretion.