Effects of chronic retinoid administration on pituitary function.

It has been reported that retinoids may affect hypothalamic-pituitary-thyroid axis, causing central hypothyroidism. In the present study, we evaluated pituitary function in 11 male psoriatic patients at baseline and after 1 and 3 months of treatment with acitretin (all-trans retinoic acid, 35 mg/day). Serum LH, FSH, testosterone, cortisol, GH and IGF-I levels were not affected by the treatment. By contrast, we observed a significant decrease in TSH levels (from 0.92 +/- 0.3 to 0.80 +/- 0.3 mU/I, p < 0.05) at 1 month, that reverted to baseline after 3 months. No change in free T4 (FT4) levels occurred, while free T3 (FT3) levels were reduced at 1 and 3 months (from 6.7 +/- 0.5 to 6.2 +/- 0.3 and 6.1 +/- 0.6 pmol/l; p < 0.05, respectively). Moreover, acitretin treatment induced a significant reduction of PRL levels after 3 months (from 182 +/- 70 to 150 +/- 56 mU/l, p < 0.05). During treatment, no change in TSH and PRL response either to TRH or dopamine infusion was observed. In conclusion, we demonstrated that treatment with low dose of acitretin induced a series of hormonal modifications that, in addition to a mild and transient reduction of TSH levels, included a persistent reduction of FT3, probably due to changes in thyroid hormone metabolism, and a decrease in PRL levels.