The pathogenic significance of progesterone in pyometra in bitches was investigated by evaluating the stages of the oestrous cycles of 369 bitches with pyometra. Concentrations of progesterone and oestradiol were determined in 100 bitches with pyometra before ovariohysterectomy. Six bitches with pyometra with progesterone > 5 ng ml-1 and oestradiol < 25 pg ml-1 were treated with the antigestagen RU 46534 (6 mg kg-1, s.c.) twice on day 1 and once on days 2, 3 and 4; ovariohysterectomy was performed on day 6. Six control bitches that met the same criteria were ovariohysterectomized and uterine morphology was compared with that of the treated bitches. The effects of treatment were monitored by hormone, ultrasonographic imaging and histomorphological studies. The results confirm that pyometra may occur at any stage of the reproductive cycle and that most animals are in the phase of dioestrus. Uterine mass (g kg-1 bodymass) with versus without content was not different in treated bitches and was significantly lower (P < 0.01) than in the control bitches. In all six dogs general clinical conditions improved during the observation period; 23.5 +/- 11.1 h after the start of antiprogestin treatment a profuse, purulent vulval discharge was observed. The effusion was nearly complete at day 6. The maximal detectable uterine lumen varied between 23 and 39 mm in diameter, it was no longer detectable on day 6. Oestradiol concentrations remained constant while progesterone decreased with distinct individual variations. Morphometrical examination of the endometrium revealed no differences between groups. The data suggest that antigestagen treatment is a promising approach for treatment of pyometra in bitches.
