Objectives: Effects of administration of combination of physiological and high doses of Ethinyl estradiol and Levonorgesterel on the lung total proteins, DNA and RNA their role for induction of lung growth or as lung mutagenic agents were studied.

Material and Methods: The study included 100 mature female albino rats. They were divided into two groups, I and II. Group I included 50 rats randomly divided into 40 rats treated with 1.75ug Ethinyl estradiol plus 15 ug Levonorgestrel in 0.5 silicon oil. Group II: 40 rats treated with 14ug Ethinyl estradiol plus 5mg Levonorgestrel in 0.5 ml silicon –oil in addition to 10 rats treated by 0.5 ml silicon oil and represented the control group. Lung tissues were used for the determination of total protein, DNA and RNA contents.

Results: Ethinyl estradiol at 1.75ug plus 15 ug Levonorgestrel produced insignificant decrease of the total protein content, significant decrease of the DNA (P<0.001) and insignificant decrease of the RNA content. Insignificant increase of total protein/DNA ratio and RNA/DNA ratio. No histopathological abnormalities were detected. Meanwhile, Ethinyl estradiol at 14ug plus 5mg Levonorgestrel produced insignificant increase of the total protein content, significant decrease of the DNA (P<0.001) and insignificant increase of RNA content. Significant increase of the total protein/DNA ratio (P<0.01) and the RNA/DNA ratio (P<0.001) was found.
The absence of any histopathological changes is suggestive that these changes are reflections of the functional performance of the lung associating the use of combined dose of estrogen and progesterone.

Conclusion: Absence of any structural and vascular abnormalities upon histopathological examination could be considered as indicative that these various changes are secondary to the state of functional performance of the lung associating the use of combined dose of estrogen and progesterone. Meanwhile, both steroids seem to have no toxic or mutagenic effects in the doses used.