1. We have validated a scintiscanning method for measuring fasting-state gall-bladder (GB) filling in man. 99mTc-labelled diethyl phenylcarbamoylmethyliminodiacetate (Tc-HIDA) was given intravenously, and 90 min later GB and gut activity were measured by using two isosensitive rectilinear scanning heads (anterior and posterior). Studies with a phantom GB in vitro, and studies in man in vivo, showed that the maximum error due to differences in isotope depth was 8%, compared with 300% when only one head was used.

2. By combining this technique with measurement of biliary lipid concentrations of fasting-state GB bile obtained by nasoduodenal intubation and intravenous cholecystokinin infusion, we were able to measure for the first time the total mass of all three biliary lipids in the GB. GB bile samples obtained in this way were divided into three consecutive portions of equal size in order to assess GB mixing. Bile acid pool size was also measured by isotope dilution.

3. We studied 12 healthy non-obese men. Fasting-state GB filling over 90 min (mean ± sem) was 54 ±8%. Biliary lipid mass in GB was 4.9 ±0.5 mmol for bile acids (67 ± 5% of the total bile acid pool), 1.6 ±0.2 mmol for phospholipid and 0.5 ± 0.1 mmol for cholesterol. The three consecutive portions of fasting GB bile gave values of 1.05 ± 0.07, 1.05 ± 0.06 and 1.03 ±0.10 for cholesterol saturation index (SI) and 6.6 ±1.1, 7.4 ± 1.6 and 6.5 ± 1.0 for Tc-HIDA c.p.m. × 1000 per mmol of bile acids.

4. The SI of fasting-state GB bile was significantly correlated with fasting-state GB filling (r = 0.63; P < 0.05). It was also correlated with cholesterol mass in GB (r = 0.64; P < 0.05), but not with bile acid and phospholipid mass.

5. We conclude that: (a) valid measurements of GB filling can be made in man by a simple scintiscanning technique employing 99mTc-HIDA as a biliary marker; (b) biliary lipid mass can also be measured if GB bile is obtained; (c) SI in health is in part determined by the degree of fasting-state GB filling, and in part by cholesterol mass in GB; (d) fasting-state GB content is well mixed in health.

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