Abstract: Objective To investigate the role of 44/42 MAPK on the apoptosis of adrenocortical cells induced by cadmium chloride(CdCl₂)in vitro.Methods The male guinea pigs' adrenocirtical cells were dispersed and primarily cultured for 24 hrs,and incubated with CdCl₂ at doses of 0,12 15,25,50,100 or 200μmol/L for 1 h.Then the phosphorylation level of P44/42 and the protein expression level of c-Fos were measured with SDS-PA GE and Western-Blot.The cells were incubated with the same doses of CdCl₂ for 2 h,then cell apoptosis rate was detected with flowcytometry.The phosphorylation level of P44/42 and the protein expression level of c-Fos were detected after the cells were treated with 100μmol/L CdCl₂ for 0,15,30,60,90,120 minutes respectively after the treatment.The cell apoptosis was detected at 0,0.5,1,2,3 or 4 hours.Results The average percentage of apoptotic cells increased with dosage(0～200μmol/L for 1 h,from 1199% to 73.48%)or duration(100μmol/L for 0～4 h,from 1.04% to 71.55%)of CdCl₂.At dosage of 0～200μmol/L,CdCl₂ could remarkably increase the phosphorylation level of P44(from 100% to 418%),the phosphorylation level of P42(1.1 times to 2.3 times),and the expression level of c-Fos(1.6 times,2.2 times,2.4 times,3.3 times or 2.8 times).100μmol/L CdCl₂ could remarkably increase the phosphorylation level of P44(1.5 times to 6.3 times),the phosphorylation level of P42(1.1～2.1 times),and the expression level of c-Fos(from 2.6 times to 4.1 times)when the cells were cultured with CdCl₂ for 0～2 hours.Conclusion CdCl₂ could induce apoptosis of adrenocortical cells through the over-phosphorylated P44/42 and in turn the over-expression of c-Fos.