Hi Angélique,
If you search "sublingual" on this forum, you will see there are many discussions of this. Sublingual administration definitely results in higher serum estradiol levels. I have cited one of the classic papers on this, as have others: "Single-Dose Pharmacokinetics of Sublingual vs Oral Estradiol Administration of Micronized 17-beta-Estradiol" , Price, T. M., et al., Obstetrics and Gynecology, Vol. 89, No. 3, 1997, pp 340-345. You can Google it.
Regarding the rapid fall of E2 levels following administration, this may be immaterial. There is evidence that the total bioavailability AUC (area under the curve) is more accurately correlated with biological effects, not peak serum levels: "Pharmacology of estrogens and progestogens: influence of different routes of administration" H. Kuhl, Climacteric, Vol. 8, Supplement 1, pp. 3-63 (2005).
@fefi -estradiol valerate should absorb very well sublingually, as it is even more lipophilic than estradiol.
Hope that helps.
With kindness,
Terri
Edit: Here is a link to the first paper -
https://www.ncbi.nlm.nih.gov/pubmed/9052581.