Validity of hypothalamic-pituitary testing in hyperprolactinemia: prolactin responses to insulin hypoglycemia and...

The release of prolactin (PRL) following insulin tolerance testing (ITT) and arginine infusion was studied in four groups of women: normal volunteers, amenorrheic women with normal PRL levels, and hyperprolactinemic women with and without roentgenographic evidence of pituitary adenoma. Women with normal serum PRL concentrations were found to have an increase in peripheral PRL and both testing modalities. Hyperprolactinemic women, whether or not there was evidence of a pituitary adenoma, did not appear to have a PRL response to either of these tests. Based on the percent change of PRL over basal values, there was a significant difference between the euprolactinemic and hyperprolactinemic groups (p less than 0.01 for insulin and p less than 0.05 for arginine). Our data indicate that in women with hyperprolactinemia neither ITT- nor arginine-induced PRL release can be utilized to discriminate between the presence and absence of an adenoma. This poor PRL response to ITT and arginine in the hyperprolactinemic patients could be the result of hypothalamic dysfunction.