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
gland, and after
parturition only one gland was milked. Biopsies were taken
from the mammary
glands of three goats at 14 d intervals during involution
and the start of the following
lactation. A histochemical method was used to visualize
sites of CA activity. To
follow the involution process, milk (liquid) samples were
taken from both teats each
week and analysed for pH and composition. The time course
of CA activity
disappearance 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 alveoli in the lactating gland. CA
activity gradually decreased in the drying gland, although
the other gland was being
milked. After 8 weeks involution the dried gland had a
significantly lower number of
stained capillaries than the milked gland. Almost no
stained capillaries were found
during late pregnancy, when both glands were dried and
the tissue growth maximal.
During lactation milk pH was 6·6±0·3 and
this increased to 7·0±0·1 in the course of
involution. In the last trimester 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. The CA
activity reappeared in the capillaries directly after
delivery, but only in the milked
gland. Clearly the regulation of CA activity is influenced
more by local than by
systemic factors and is associated with the metabolic
activity of milk secretion.