Effects of somatostatin on intestinal calcium absorption in man with primary hyperparathyroidism

Eight patients suffering from primary hyperparathyroidism were studied in basal conditions, i.e. during a saline infusion and under somatostatin administration (a 250 micrograms bolus injection followed by continuous infusion of 500 micrograms per hour over 240 min). The calcium metabolism was estimated from (i) concentrations of plasma calcium, phosphorus, 25-hydroxyvitamin D (25-OH-D), iPTH and (ii) intestinal calcium absorption determined by a double radiotracer technique using oral 47Ca and IV 45Ca. The results show that somatostatin produced no significant change in calcium, phosphorus, 25-OH-D or iPTH levels. On the contrary, the fractional absorption of calcium (FA Ca), expressed as a percentage of the total oral dose and measured at 30 minute intervals over 240 min, was significantly depressed with somatostatin during the first 2 hours. Beyond the second hour FA Ca remained slightly depressed with somatostatin, but was not significantly different from the basal conditions. From the present results, we conclude that somatostatin slows down calcium absorption, while the total amount of calcium absorbed at the completion of the absorption process is not significantly diminished. Furthermore, as 25-OH-D and iPTH remained unchanged, somatostatin seems to have no effect on the hormonal control of calcium absorption. Therefore, we suggest that somatostatin has only a mechanical effect on calcium absorption, slowing down the intestinal transit.