I am not sure how nolvadex would cause estrogen rebound, could you expand on that?
If we were talking about Arimidex, I could understand.
Aromatase inhibitors have been shown to exert a positive feedback on aromatase production by increasing pituitary LH secretion as a response to lowered estrogen levels.
LH secretion not only stimulates testosterone production, it also induces testicular aromatase.
This is why gyno is so common in people using HCG, which acts like LH.
Endocr Relat Cancer 1999 Jun;6(2):211-8
Aromatase inhibitors and enzyme stability.
Harada N, Honda SI, Hatano O.
Department of Biochemistry, Fujita Health University School of Medicine, Toyoake, Aichi, Japan.
The effects of two steroidal (4-hydroxyandrostenedione and atamestane) and three non-steroidal (fadrozole, vorozole, and pentrozole) aromatase inhibitors on the levels of aromatase mRNA and protein were examined in vitro and in vivo. Immunocytochemistry revealed increased quantities of immunoreactive aromatase in human choriocarcinoma-derived JEG-3 cells in response to pretreatment with the non-steroidal inhibitors. To elucidate this effect in detail, aromatase protein in JEG-3 cells after treatment with various inhibitors was quantified using an enzyme-linked immunosorbent assay (ELISA). A time-dependent increase in aromatase protein in the cells was observed with all the aromatase inhibitors except 4-hydroxyandrostenedione, whereas aromatase mRNA levels in the cells remained unchanged during the inhibitor treatment. The three non-steroidal agents caused an approximately fourfold increase in aromatase protein in the cells 24 h after the treatment, as compared with untreated controls. The increase in aromatase protein in the cells was not blocked by treatment with cycloheximide, an inhibitor of protein synthesis. The inhibitors also appeared to block the rapid degradation observed in JEG-3 cells after induction by forskolin. In vivo, daily injection of the inhibitors into adult female mice caused increases in levels of both aromatase mRNA and protein in the ovary. The increase in aromatase mRNA in this in vivo study could be explained by an increase in gonadotropin concentrations in response to decreased plasma concentrations of estrogens. In conclusion, we suggest that aromatase inhibitors increase aromatase protein through stabilization and reduced protein turnover