| Abstract: | Somatostatin and gastrin-like immunoreactivity was measured in peripheral venous plasma at 22, 24, 02, 04 and 06 hours in 10 experiments performed on 6 healthy volunteers. In five of the experiments the subjects had been pretreated with propranolol 20-40 mg three times daily for one week. At 22 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 approximately 10 and 60% of the 22 h value, respectively. Somatostatin levels reached their lowest value at 02 h (50%) of the 22 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 02 h dip in somatostatin levels. It is suggested that the nocturnal dip in somatostatin secretion is vagally mediated and that the peak in acid output occurring at this hour is 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. |
