The objective was to investigate the effect of proligestone on the secretion patterns of feline ovarian steroids for a 12-week period after its single and repeated administration.

Serum concentrations of oestradiol-17β (pg/ml) and progesterone (ng/ml) were quantified by enzyme-immunoassays in serial samples (15/animal) of 18 cats treated with proligestone (33 mg/kg, sc) once (n=6), twice (n=6) and 3 times (n=6) and of 4 untreated cats (controls). The 1st proligestone administration was performed during oestrus, the 2nd and the 3rd one 12 weeks after the 1st and the 2ndone, respectively. Controls were judged to be at the stages of oestrus (O, n=22), interoestrous interval (I, n=10) and dioestrus (D, n=28) based on behaviour and progesterone concentrations. Data were subjected to nonparametric tests (Kruskall Wallis & Mann Whitney U test, P<0.05) and are expressed as median (25^th-75^th percentiles).

In controls, oestradiol-17β concentrations at O [44.0 (34.0-59.0)] were significantly higher than those at I [25.0 (21.0-30.0)] and D [21.5 (16.0-34.0)]. Progesterone concentrations at D [20.6 (15.5-35.0)] were significantly higher than those at O [0.9 (0.7-1.3)] and I [1.0 (0.9-1.4)]. In once proligestone-treated cats, low oestradiol-17β concentrations, similar to those of I-D in controls, were detected on days 2-49. Then, they increased to O levels on days 56, 70, 77 and 84 (without being accompanied by respective behaviour). Progesterone concentrations were generally low, similar to those of O and I in controls. However, on days 14 and 21, they did not differ significantly from those of D in controls, either. In twice and three times proligestone-treated animals, oestradiol-17β levels ranged from particularly low, in the majority of cases till days 21 and 49, respectively, to low, similar to those of I-D in controls, thereafter. Progesterone concentrations till day 56 and day 84, respectively, were significantly lower than those of O and I in controls.

Results indicate that proligestone exerts a suppressive effect on serum oestradiol-17β and progesterone concentrations, which seems to be more profound and prolonged after its repeated administration. However, proligestone administration during oestrus does not guarantee inhibition of ovulations.