THE EFFECTS OF METERGOLINE COMBINED WITH PGF(2-ALPHA) TREATMENT ON LUTEAL FUNCTION AND GESTATION IN PREGNANT BITCHES

This study was designed to determine the nature of the antiluteotrophi c effect of metergoline on pregnant bitches, the occurrence of clinica lly evident side-effects, and the efficacy of PGF(2 alpha), in initiat ing abortion after a course of metergoline therapy. Starting on Days 1 8 to 20 after the onset of diestrus, 8 adult pregnant beagle bitches w ere treated twice daily with 0.4 to 0.5 mg/kg po metergoline for 5 d. After receiving no treatment for the next 5 d, metergoline administrat ion was repeated for a further 3 d, followed by twice-daily intramuscu lar injections of dinoprost tromethamine at 250 mu g/kg. There was an overall trend for the plasma progesterone concentration to decrease du ring the first and second course of metergoline therapy and to rise du ring the intervening period of no treatment. None of the bitches abort ed during or after the first 5 d of metergoline administration. No sid e-effects were evident during the metergoline therapy. After pretreatm ent with metergoline a mean of 4.8 injections of PGF(2 alpha) was nece ssary to ensure complete abortion. All abortions were rapid and uneven tful, except for the usual side-effects associated with PGF(2 alpha). The plasma progesterone concentration at the onset of PGF(2 alpha) tre atment was positively correlated to the number of PGF(2 alpha) injecti ons needed to complete the abortion process. The plasma progesterone c oncentration was < 8 nmol/l for several days as a result of metergolin e therapy in 6 of the 8 bitches. Only 1 bitch, however, aborted before PGF(2 alpha) therapy was initiated. In the other 7 bitches PGF(2 alph a) appeared to be necessary for abortion. The results suggest that the effect of metergoline has to be considered incompletely luteolytic at the doses used in this study. Even prolonged suppression of luteal fu nction in early to mid-gestation, however, did not cause abortion with out the previously documented luteolytic and/or ecbolic effects of PGF (2 alpha) The average interestrus interval of cycles treated with mete rgoline and PGF(2 alpha) was shorter (mean 182.2 d, SD 7.9 d, n = 6) t han expected for this group of bitches (mean 211.4 d, SD 31.5 d, n = 7 ).