Comparative effects of proligestone and megestrol acetate on basal plasma glucose concentrations and cortisol responses to exogenous adrenocorticotrophic hormone in cats.

Cats were given megestrol acetate (MA, 5 mg once daily for 14 days), subcutaneous proligestone (PRG, 100 mg on two occasions one week apart) or subcutaneous saline (1 ml as for PRG). In cats given saline (n = 6) basal cortical concentrations, cortisol concentrations after adrenocorticotrophic hormone (ACTH) administration and fasting blood glucose concentrations did not change significantly during the following seven weeks. Cats given MA (n = 7) developed suppression of basal and ACTH-stimulated cortisol concentrations and fasting hyperglycaemia during treatment. Effects on cortisol persisted for two weeks after MA dosage ceased. In cats given PRG (n = 7), basal cortisol concentrations were reduced overall, but only three cats had persistently suppressed post-ACTH cortisol concentrations. Adrenal suppression continued for 14 weeks in one of these and for at least 22 weeks in two cats. Fasting blood glucose concentrations were unchanged in PRG-treated cats.