RELATIONSHIP BETWEEN FRACTIONAL CALCIUM-ABSORPTION AND GASTRIC-EMPTYING

The relationship between calcium absorption and gastric emptying and t he precision of measurement of fractional calcium absorption using a s ingle isotope technique were evaluated in 14 normal postmenopausal wom en (age range 61-72 years). On two occasions separated by between 5 an d 15 days, each subject was given 250 mL water containing 0.2 MBq of C a-45 in 20 mg of calcium carrier as the chloride, 20 mg kg(-1) paracet amol and 9 MBq of Tc-99m sulphur colloid. Venous blood samples were ta ken at -2, 15, 30, 45, 60, 90, 120, 150 and 180 min after consumption of the drink, and gastric emptying (GE) was monitored with a gamma cam era. Fractional calcium absorption in the first hour (alpha(6)) was ca lculated from the blood samples obtained at 15, 30, 45, 60, 90 and 120 min. An absorption rate was also derived from the 60 min sample using only a calibration curve (alpha(1)). There were close correlations be tween radiocalcium absorption on the two study days (r = 0.89, P < 0.0 01 for both alpha(1) and alpha(6)) and between alpha(1) and alpha(6) ( r = 0.93, P < 0.001). Plasma paracetamol concentrations at 15 min were directly related to the early phase of GE (r = 0.42, P < 0.05). In co ntrast, calcium absorption was inversely related to GE (r = 0.45, P < 0.05). We conclude that radiocalcium absorption is not greatly influen ced by gastric emptying rate and that the single blood sample procedur e has similar precision to the six-blood sample test.