Recovery pattern of hypothalamo-pituitary-testicular axis in patients with macroprolactinomas after treatment with cabergoline

BACKGROUND & OBJECTIVES: Hyperprolactinaemia affects testicular functions by influencing hypothalamo-pituitary-testicular (HPT) axis at various levels. Available literature on the level of defect, time course of improvement of gonadal functions and its relation with decline in prolactin levels is scanty. We carried out this study to evaluate the HPT axis in patients with macroprolactinomas, before and six months after cabergoline therapy. METHODS: Fifteen men with macroprolactinomas underwent gonadotropin and testosterone response to their respective stimuli before and after six months of cabergoline therapy. RESULTS: Serum prolactin levels decreased after six months of therapy. Pretreatment, mean lutenizing and follicle stimulating hormones (LH and FSH) levels were 2.0 ± 0.4 and 1.4 ± 0.2 IU/l, respectively. However, LH and FSH responses to GnRH were preserved in majority of the patients and LH peaked to 12.1 ± 2.3 IU/l (P<0.01), while FSH to 2.9 ± 0.4 IU/l suggesting the influence of hyperprolactinaemia at the level of hypothalamus with preserved gonadotrope reserve. After cabergoline therapy, there was an increase in basal as well as stimulated LH and FSH levels, though these were not statistically significant when compared to respective pretherapy levels. Basal testosterone (T) levels significantly improved after therapy, but peak T response to hCG was similar at both pre- and post treatment. A significant correlation was observed between peak LH and peak T at baseline (r=0.53, P<0.01) and it further strengthened after therapy (r=0.70, P<0.01). After cabergoline therapy, there was significant improvement in seminal volume, sperm count and motility and sperm count correlated with peak FSH response (r=0.53, P<0.05). INTERPRETATION & CONCLUSIONS: Hyperprolactinaemia affects testicular functions probably by influencing at the level of hypothalamus resulting in subnormal basal secretion of gonadotropins required for optimal testicular functions.