Nocturnal variation in plasma levels of gastrin and somatostatin-like immunoreactivity in man

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Abstract
Somatostatin and gastrin-like immunoreactivity was measured in peripheral venous plasma at 2200, 2400, 0200, 0400 and 0600 h in 10 experiments performed on 6 healthy human volunteers. In 5 of the experiments, the subjects were pretreated with propranolol 20-40 mg 3 times daily for 1 wk. At 2200 h gastrin and somatostatin levels averaged 153 and 143 pg/ml without treatment with .beta.-blockers and 93 and 74 with such treatment. Gastrin and somatostatin levels fell during the course of the night to .apprx. 10 and 60% of the 2200 h value, respectively. Somatostatin levels reached their lowest value at 0200 h (50%) of the 2200 h value. Treatment with .beta.-blockers tended to decrease gastrin as well as somatostatin levels over the whole experimental period, but did not influence the gradual decline of gastrin and somatostatin levels occurring during the night or the 0200 h dip in somatostatin levels. The nocturnal dip in somatostatin secretion may be vagally mediated. The peak in acid output occurring at this hour may be due to the decreased output of gastric somatostatin. The fact that the nightly dip in somatostatin secretion coincides with the peak output of the pituitary hormones prolactin and growth hormone is discussed.

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