Calcitonin-like immunoreactivity in the pituitary vascular bed of man

The calcitonin-like immunoreactivity (CT-like immunoreactivity) was measured in blood aspirated from the vascular bed of the anterior pituitary gland during transsphenoidal surgery in 33 patients with PRL-producing microadenomas, 2 patients with Cushing's disease, and 1 patient with metastatic breast cancer with a normal pituitary gland. The mean level of CT-like immunoreactivity in the pituitary vascular bed was 2-3 times higher than in peripheral blood (2.4 +/- 0.9 ng/ml vs. 0.69 +/- 0.19 ng/ml), and the difference was highly significant (P less than 0.001). However, the serum ACTH, hGH, TSH, PRL, and FSH in the pituitary vascular bed was 1000 times or higher than that found in the peripheral blood. The serum CT-like immunoreactivity levels in the pituitary bed in the two patients with Cushing's disease were similar to that found in other patients. Our investigations indicate: 1) CT-like immunoreactivity in man is higher in the blood obtained from the pituitary vascular bed than that found in the peripheral blood; 2) the serum CT-like immunoreactivity level in the pituitary vascular bed is much less than ACTH or the other hormones secreted by the pituitary gland; 3) there is no correlation between CT-like immunoreactivity and ACTH levels.