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Pyometra is a serious and potentially fatal disease of the uterus that results from hormonally induced changes in the uterus' lining, the endometrium, that allows infection to occur. The patency of the cervix (open vs. closed) influences the severity of the disease, its prognosis, and the treatment options; however, it also may occur in the spayed female that was left with an excessively long uterine stump after her hysterectomy. The stage is set for the development of pyometra when ovulation occurs because the ovaries produce progesterone in preparation for pregnancy. If conception happens, then pyometra is not likely to occur. If conception does not occur, then the endometrium, which has undergone glandular enlargement, may continue to enlarge. The latter scenario results in excessive accumulations of secretions which are an ideal medium for bacterial growth. The increased progestrone level inhibits the drainage of the uterus and also inhibits leukocyte function, which is necessary to ward off infection. The most common bacterial organism that has been cultured from the pus of pyometra has been Escherichia coli (E. coli) which has been found to have a specific affinity for the progesterone-sensitized endometrium. Bacterial infections usually originate from contamination entering the uterus through the open cervix. Female hormones, such as progesterone in the form of megestrol acetate (Ovaban) and diethylstilbestrol (DES), have been used therapeutically for other diseases and may artificially sensitize the endometrium and induce the proper setting for pyometra also. Pyometra is usually seen in the older intact bitch or queen. Younger intact females that have undergone hormone therapy are also prime candidates for pyometra.		The clinical signs become evident about 30-60 days post-heat cycle or post-hormone therapy. The severity of the condition depends upon the patency of the cervix, any underlying concurrent medical conditions, and the age the patient. Closed pyometra, in which the cervix is closed the acts as a barrier to uterine drainage, is the most serious and life threatening of the two. Lethargy, depression, loss of appetite, and abdominal distention are common early signs. As the pus formation continues to swell the uterine vessel, rupture may occur thereby producing a potentially painful, fatal peritonitis or a septic toxemia (blood poisoning) may develop or both could happen. Vomiting, dehydration, anemia, and diarrhea may result from the toxemia of pyometra and/or from the frequently associated uremic poisoning. Ovariohysterectomy (spaying, fixing) is the treatment of choice. It never fails to astound me when I see how immense the pus-filled uterus can be. In some cases, the swollen uterus is nearly as large as the patient once it was removed and placed next to the dog or cat. Surgery is not without possible complications. Should the pus-filled uterus rupture before or during surgical intervention and the toxic contents spill into the abdominal cavity, then peritonitis will result. Then the patient dies a painful death. Dr. Johm N. Case, Jr. is the owner of the Clinic for Animals, 5201 North State Road, Tamarac, FL (954) 739-4500. Dr. Case has a companion animal practice.