OBJECTIVE: To investigate the effects of PDGF on the proliferation of rat HSC, its gene expression of collagens and the autocrine excretion of PDGF in vitro. METHODS: (3)H-TdR incorporation was used to estimate the DNA synthesis elicited by PDGF, TGF-beta1 and EGF in HSC cultured in an absolutely serum-free medium. Northern blot was employed to detect the levels of mRNA expressions of type I and III procollagens and PDGF induced by PDGF added in the same medium for HSC. RESULTS: Both PDGF and EGF enabled to stimulate the proliferation of HSC in a dose-dependent manner, and the effect of the former was stronger. The proliferation was dose-dependently increased in PDGF and EGF with a dosage between 0.5 and 10 ng/ml, and the synthesis of DNA became saturated when the dosage was over 10 ng/ml. TGF-beta1 gave no effects on the proliferation of HSC under current experimental condition. Furthermore, PDGF was able to enhance the mRNA expression for type I and III procollagens and PDGF itself. The promoting effect for the expressions of type I and III procollagen mRNAs by PDGF was bi-phasic between 6 to 48 hours of the cultivation. For type I procollagen, mRNA expression began to increase 12 hours after PDGF stimulation, and the increase became prominent at 48 hours. For type III procollagen, an increase of mRNA expression was seen before the stimulation of PDGF, and the expression level was comparatively increased 48 hours later. The mRNA expression of PDGF was increased by 2-3 times 6 hours after PDGF stimulation, and back to the original level 24 hours later. CONCLUSIONS: PDGF enabled to promote the proliferation of HSC and expression of collagens in HSC. The bi-phasic effect on the expression of collagens may be interrelated with the autocrine excretion of PDGF.