Effect of megestrol acetate on the endometrium of the prepubertally ovariectomised kitten

Five prepubertally ovariectomised kittens served as controls. Ten prepubertally ovariectomised kittens were given megestrol acetate (MA) orally at the rate of either 5 or 15 mg twice weekly for 12 to 13 weeks. The uterine horns of treated cats increased in length and diameter. The endometrium became deeply folded with marked hypertrophy of glandular epithelium and production of glycogen by the glandular cells. One cat developed pyometra. Once weekly administration of 2.5 mg MA for a further 12 weeks maintained the hypertrophic changes. The proliferated endometrium regressed considerably but not completely after 12 weeks without MA administration. In two other kittens 2.5 mg MA once weekly for six weeks was sufficient to induce similar changes. MA is a very potent progestational agent in cats, even if they have been ovariectomised prepubertally.