Rat pituitary adenoma and hyperplasia induced by caffeine administration

The effect of caffeine by oral administration on female Wistar rats was studied for 12 months. High concentrations (2000 micrograms/mL) of caffeine caused a decrease in body weight and an increase in the weight of the pituitary gland in these rats. Increased pituitary weight was caused by the growth of a pituitary adenoma or hyperplasia. Pituitary adenomas and instances of hyperplasia were found in 27 of the 40 rats in the caffeine group, compared to 9 of the 30 rats in the control group. The histologic classification used was microadenoma, papillary (or sinusoidal) macroadenoma, and diffuse macroadenomas. These adenomas appeared to be endocrinologically nonfunctioning.