PURPOSE: GH-releasing peptide(GHRP-6) was shown to possess strong GH-releasing activity both in vitro and in vivo. Chemically,GHRP-6 has no primary sequence homology with GHRH. The GH releasing activity of GHRP-6 has been demonstrated in several animal species including humans. GHRPs could have a considerable physiological and clinical useful for treatment of GH deficient and/or non GH deficient short children in the near future. The aim of this study was to evaluate the GH-releasing activity of GHRP-6 in anterior pituitary cell culture and compared to that of GHRH . METHODS: Spraque-Dawley rats were decapitated and pituitary glands were collected in ice-cold PBS. The anterior pituitaries were minced into small fragments and dissociated by enzymatic digestion. These pituitary cells were suspended in Dulbecco' modified Eagle' medium(DMEM) with fetal calf serum at a concentration of 106cells/mL and then plated onto multiwelled dishes at a density of 1.5*05 cells per 6 well plate. GHRP-6 treated group(10-8, 10-7, 10-6 M), GHRH treated group(10-8, 10-7, 10-6 M) and combined GHRP-6 and GHRH treated group were classified. After replacement of each GHRP and/or GHRH+GHRP, the released GH were measured with RIA in 10 min, 20 min, and 30 min. RESULTS: 1) GHRH(10-8) treatment increased GH release by 15.8+/-3.9ng/mL in 0 min., 69.8+/-4.3ng/mL in 10 min. 78.3+/-5.0ng/mL in 20 min. and 67.8+/-7.2ng/mL in 30 min. In case of GHRP-6(10-8M) treatment increased GH release by 11.0+/-1.4 in 0 min., 90.3+/-12.2 in 10 min., 78.3+/-4.5ng/mL in 20 min. and 78.0+/-4.8ng/mL in 30 min. The released GH levels were markedly increased in 10 min. after GHRP-6 and were not singificantly different from that of GHRH. 2)GHRP+GHRH(10-7M+10-8M) treatment increase GH release by 8.8+/-1.5ng/mL in 0 min., 37.8+/-9.3ng/mL in 10 min., 41.3+/-8.1ng/mL in 20 min. and 40.0+/-7.9ng/mL in 30 min. The released GH levels after GHRP+GHRH treatment was not markedly increased statistically compared to GHRH only. CONCLUSION: GHRP-6 could release GH in rat anterior pituitary cell culture and the released GH amounts were not significantly different from that of GHRH. There was no synergistic additive effect in GHRP+GHRH in rat pituitary cell culture.