Oral Contraceptive Steroids as Promoters of Hepatocarcinogenesis in Female Sprague-Dawley Rats

A number of reports have described the occurrence of liver cell adenomas in women using oral contraceptives. Circumstantial evidence derived from human and early experimental animal data, together with the recent report of Taper [Cancer (Phila.), 42: 462–467, 1978], suggests that oral contraceptive steroids may be liver tumor promoters. The objective of this study was to determine whether the feeding of two commonly used oral contraceptive steroids, mestranol and norethynodrel, can promote diethylnitrosamine (DENHnitiated hepatocarcinogenesis. Female Sprague-Dawley rats were partially hepatectomized and intubated with either water or DEN (5 mg/kg body weight) 24 hr later. Twenty-four hr after carcinogen treatment, the animals were separated into seven groups (15 rats/group). The treatment groups were as follows: DEN → mestranol, DEN → norethynodrel, DEN → mestranol plus norethynodrel, DEN → 0.05% phenobarbital, DEN → basaldiet, H₂O → phenobarbital, and H₂0 → mestranol plus norethynodrel. Steroid consumption was mestranol = 0.02 to 0.03 mg/kg body weight/day and norethynodrel = 0.5 to 0.75 mg/kg/day. These doses are equivalent to 10 to 15 times the human dose. Five animals from each group were killed after 4 months and ten after 9 months. Histochemically detectable γ-glutamyl transpeptidase positive foci, together with hematoxylin and eosin-detectable lesions and γ-glutamyl transpeptidase enzyme activity were scored in each liver. At both kill times, DEN-initiated animals fed diets containing mestranol, mestranol plus norethynodrel and phenobarbital had significantly greater numbers of γ-glutamyl transpeptidase foci (p < 0.05) than did the controls. In addition, DEN-initiated animals fed diets containing mestranol or mestranol plus norethynodrel had greater numbers of basophilic foci than did animals in the other groups. These results suggest that the oral contraceptive steroid mestranol is a promoter of the appearance of putative precursor lesions of hepatocarcinogenesis.