It is widely known that the bile is considerably concentrated as well as
acidified within the gall bladder. However, the underlying mechanism(s) is not
clear at present. In order to understand these processes, various solutions were
introduced into the gall bladder which was previously cannulated and the changes in
the volume and the composition were determined.
1) Permeability Characteristics of Gall Bladder:
10ml. of soltions of NaCl, urea, and sucrose isosmotic with plasma were
introduced into the gall bladder, and changes in volume were followed for a period
of 2 hrs. Distilled water was also used for comparison. The gall bladder wall was
highly permeable to urea and distilled water and less permeable to NaCl, while it
was not to sucrose.
When various sucrose solutions(0.1, 0.2, 0.3, 0.4, 0.5M/L) were introduced and
the changes in the volume were followed until non further change could be detected
at least for 1 hours, the final fluid volume within the gall bladder varied as a
function of the existing osmostic pressure gradient, indicating that the gall
bladder under some conditions resembles an osmometer, thus the transport of water
through gall bladder wall was carried out by a passive mechanism.
2) Concentrating Mechanisms:
When the various mixtures of isosmotic sucrose, NaHCO^^3 and NaCl solutions were
introduced into the gall bladder, and the change in the volume as well as in the
concentration of certain electrolytes(e.g. Na**+, Cl**- and HCO^^3 **-) were
followed until no further changes could be detected for at least 1 hour. The gall
bladder wall as able to absorb these electrolytes and there was a corresponding
reduction in the volume. The final lowest concentrations of Na**+, Cl**- and
HCO^^3**- were found to be approximately 20, 10 and 10 mEq/L, respectively. These
values are much lower than those of plasma, indicating that electrolytes are
transported against the concentration gradient. Moreover, this ability to absorb
the electrolyte was abolished in presence of 10**-2 M/L of monoiodoacetic acid, but
not in presence of 2, 4-DNP, NaF or KCN, suggesting that the energy for the
electrolyte absorption is supplied by the glycolytic process. Since the gall
bladder bile, as well as the hepatic bile, was isosmotic with plasma, it is
concluded that the primary event of concentrating the bile within the gall bladder
is the active absorption of Na**+, Cl**- and HCO^^3**- accompanied by water.
3) Acidification of Bile:
The pH of the hepatic or gall bladder bile as well as artificial solutions was
highly dependent upon the HCO^^3**- concentration in them under the same pCO^^2.
Even when a large amount of Diamox was administered, the transfer rate of HCO^^3**-
across the gall bladder wall was not altered, indicating that carbonic anhydrase is
not perhaps involved in this mechanism. According to the results mentioned above,
it may be concluded that the acidification process of the bile within the gall
bladder is probably carried out by HCO^^3**- absorption and not by the H**+