Low-dose infusion of somatostatin in man--no effect upon intestinal calcium absorption but a fall in blood insulin.

We studied the role of low plasma somatostatin (SRIF) levels in intestinal calcium absorption (CaA) in man. Plasma somatostatin-like immunoreactivity (SLI; pg X ml-1) rose after a 600-cal test meal (from 22.9 +/- 2 basally to 30.6 +/- 3.6 at 45 min, p less than 0.05), but was not affected by an oral Ca load (264 mg). Under intravenous SRIF (0.15 microgram kg-1 h-1) plasma SLI rose from 3.3 +/- 0.4 basally to 24.5 +/- 3 at 45 min (p less than 0.001). CaA was not influenced under these conditions, whereas insulin levels fell significantly and the levels of PTH, calcitonin, glucagon and GH were not changed. A regulating role of SRIF in CaA seems therefore unlikely for human physiology, since neither SLI is influenced by an oral Ca load, nor is CaA changed under postprandial SLI. The fall in insulin under postprandial-like SLI levels favors the view of a hormonal role of SRIF in man.