Fine structure of pancreas in cortisone-treated guinea pigs and rabbits.

Twenty-eight male rabbits and 28 male guinea pigs received daily intramuscular injections of cortisone acetate for four to 31 days (rabbits, 5 mg/kg; guinea pigs, 10 mg/animal). Moderate hyperglycemia ensued. Insulin concentrations of the pancreatic tissue varied but were higher in cortisone-treated animals than in untreated controls. In rabbits, degranulation of beta cells, hyperplasia of islets, and proliferation of ductular structures were the major light microscopic findings. Ultrastructural studies suggested that beta cell neogenesis took place mainly within pre-existing islets but probably also within ductular structures. Mixed (acinar-islet) cells were not identified. In guinea pigs, ductular proliferation was not noted, and beta cell neogenesis appeared to take place exclusively within preexisting islets and islet cell nests. In both species, cells of several types contained glycogen deposits.