Heterogeneity of prolactin responses to oestradiol benzoate in women with prolactinomas.

Serum prolactin concentrations were measured for 72 h after intramuscular injection of 1 mg of oestradiol benzoate in six normoprolactinaemic women and nineteen with a prolactinoma (eleven with an obviously enlarged pituitary fossa and eight with a normal pituitary fossa). The group with an obvious tumour showed a rise in mean serum prolactin at 48 h to 122% of basal concentrations (p less than 0.05), and at 72 h to 137% of basal concentrations (p less than 0.01). Individual responses were variable, but in four patients serum prolactin rose to 165% or more of basal concentrations. In the group with a prolactinoma and a normal pituitary fossa serum prolactin at 72 h was 121% of basal concentrations (p less than 0.05). Normoprolactinaemic women showed no significant change in serum prolactin at any time. This study demonstrated a heterogeneity of serum prolactin responses to acute oestradiol administration in women with prolactinomas. Some patients with large tumours had a hypersensitive response to oestradiol. This heterogeneity of response could account for the present unpredictability of expansion of prolactinomas during pregnancy.