[en] In pituitary lactotrophs of female Sprague-Dawley rats given cysteamine (300 mg/kg, per os/day) for 7 days, forming granules were increased in number and contained many separate electron-dense structures suggesting crinophagy. Compared to control values, cysteamine treatment caused no change in blood prolactin (PRL) levels, measured by radioimmunoassay (RIA). 17 beta-Estradiol (50 micrograms, sc/day) for 7 days, induced lactotroph hyperplasia and increased blood PRL levels which were unaffected by simultaneous cysteamine administration. The ultrastructural changes did not reflect those due to bromocriptine suppression of secretory activity, and supported the concept that cysteamine altered lactotroph morphology by an unknown mechanism. In pituitary gonadotrophs following cysteamine treatment, increased electron lucency of luminal contents of dilated rough endoplasmic reticulum was noted; however, blood luteinizing hormone (LH) levels did not differ from those of control values. In ovariectomized rats, cysteamine suppressed castration cell formation and reduced blood LH levels, suggesting an interference with the cell's ability to respond to GnRH stimulation. The morphologic effects of cysteamine appeared to be selective to lactotrophs and gonadotrophs, and were not secondary to vascular impairment, as capillary endothelial cells were undamaged