5α-Dihydrolevonorgestrel
5α-Dihydrolevonorgestrel is an active metabolite of the progestin levonorgestrel which is formed by 5α-reductase. It has about one-third of the affinity of levonorgestrel for the progesterone receptor. In contrast to levonorgestrel, the compound has both progestogenic and antiprogestogenic activity, and hence has a selective progesterone receptor modulator-like profile of activity. This is analogous to the case of norethisterone and 5α-dihydronorethisterone. In addition to the progesterone receptor, 5α-DHLNG interacts with the androgen receptor. It has similar affinity for the androgen receptor relative to levonorgestrel, and has androgenic effects similarly to levonorgestrel and testosterone. 5α-DHLNG is further transformed into 3α,5α- and 3β,5α-, which bind weakly to the estrogen receptor and have weak estrogenic activity. These metabolites are considered to be responsible for the weak estrogenic activity of high doses of levonorgestrel.
