Adrenocortical function in the domestic cat during treatment with levonorgestrel

Levonorgestrel was administered via a subcutaneous, slow-release silastic implant to 10 queens. Five other queens served as controls. Their adrenocortical function was assessed by the adrenocorticotrophic hormone (ACTH) stimulation test before and after one, two, six and 12 months of treatment. In addition, the gross anatomy and histology of the adrenal gland were examined post mortem in six of the treated cats. In both the control and treated queens the plasma cortisol concentrations (pre and post ACTH) were significantly different (P<0.05) at different times. However, there were no significant differences between the plasma cortisol concentrations (pre and post ACTH) of the treated and control queens. No gross or microscopical abnormalities were visible in the adrenal glands of the treated queens.