EFFECT OF PANCREATIC GROWTH HORMONE RELEASING FACTORS ON GH SECRETION BY HUMAN SOMATOTROPHIC PITUITARY TUMOURS IN CELL CULTURE

Abstract

Human pancreatic growth hormone releasing factors [hpGRF(1-40) and hpGRF(1-44)] significantly stimulated GH [growth hormone] secretion when added to cell cultures of human somatotrophic pituitary tumors for 2 h. There was little difference in potency between the 2 peptides, and the response of different tumors varied, ranging from 30-500% increases in GH secretion over control levels. This stimulatory effect was blocked by somatostatin (SRIF) and bromocriptine. The suppressive effect of bromocriptine, but not of SRIF, was overcome by high doses of hpGRF(1-44). TRH stimulated GH secretion by 1 of 3 somatotropic tumors in cell culture, and potentiated the stimulatory effects of hpGRF(1-44). Thus, hpGRF apparently increase serum GH levels in man by a direct action at the pituitary somatotroph level.