The role of testosterone (T) and its metabolites, diidrotestosterone (DHT) and estradiol (E), on different physiological functions is not completely known. Ovariectomized FtM T treated represent an interesting model to study the effects of T and its metabolites on different physiological functions.

In this study, TU 1000 mg (Nebido^®) was injected in 15 FtM (week 0, 6,18, 30 and 42) alone (n=5; group A) or in combination with dutasteride 5 mg/d (n=5; group B) or letrozole 5 mg/d (n=5; group C).

Hormone, bone and metabolic parameters at baseline and at week 54 were:

TotalT (nmol/L) GROUP A 7.9±6.0, 13.6±2.6, GROUP B 7.1±6.3, 18.4±4.6§, GROUP C 4.8±4.8, 18.2±4.2§, baseline and wk 54 respectively.

E (pmol/L) GROUP A 64.4±43.4, 89.6±36.3, GROUP B 41.4±19.4, 76.0±47.4, GROUP C 37.8±23.1, 18.0±0.0* baseline and wk 54 respectively.

DHT (nmol/L) GROUP A 1.3±1.2, 2.2±0.9, GROUP B 1.0±0.7, 0.4±0.1*, GROUP C 0.9±0.7, 2.7±1.3 baseline and wk 54 respectively.

*= P<0.05% change vs group A

§= P<0.05 vs baseline

No significant changes of any parameters occurred except for bone mass density that significantly decreased in group C and lean mass that increased significantly less in group B as compared to group A. TU injections were well tolerated by all subjects.

This data suggests that TU is an optimal formulation for replacement in FtM that is well accepted and does not cause major problems. The aromatization of TU is important for maintenance of bone density while DHT may have a role in muscle mass maintenance.