Evidence of a circulating growth hormone stimulating factor other than growth hormone releasing hormone in a patient with pituitary tumour and acromegaly

Abstract. This study is a report on the growth hormone (GH) stimulatory effect of serum and plasma from a patient with notably active acromegaly due to a GH producing pituitary adenoma. Pituitary adenomatous tissue from 7 patients with GH producing adenomas, one with a prolactin (Prl) producing adenoma, one with a TSH producing adenoma, and one with a non-secreting adenoma, were cultured in vitro for 8–10 days. Media were changed every 48–72 h and contained Neumann Tytell buffer with the addition of 1) foetal calf serum, 2) patients' own serum or plasma, 3) serum or plasma from the patient with notably active acromegaly. GH release expressed as μg GH/I/48–72 h between day 6 and 8 in culture did not differ when adenomatous tissue was cultured in buffer, foetal calf serum or the patients' own serum or plasma. In contrast, GH release was increased in 9/10 patients, when media contained serum or plasma from the patient with notably active acromegaly. This GH stimulatory effect was demonstrated in vitro in human pituitary adenomatous tissue from patients with pathological as well as normal GH secretion in vivo. Furthermore, this GH releasing plasma in a concentration of 10% increased GH release in cultures of dispersed rat anterior pituitary cells. In the same system, synthetic growth hormone-releasing hormone (GRF)-44 stimulated the release of GH in a dose-dependent manner. However, at all dose levels including maximally stimulating doses of GRF, an additive effect on GH release was seen with 10% of the GH releasing plasma. These results indicate that plasma from a patient with acromegaly increases basal GH release from human pituitary adenomatous tissue and also increases basal as well as stimulated GH release from rat anterior pituitary cells in vitro. The additive effect on maximally GRF stimulated GH release, implies that the GH releasing plasma stimulates GH release at least partly by a mechanism different from that of GRF. Furthermore, these results suggest that extrapituitary factors other than GRF are involved in the release of GH from pituitary tumours.