Plasma concentrations of prolactin in overtly pseudopregnant Afghan houndsand the effect of metergoline

The effects of metergoline, a 5-hydroxytryptamine (serotinin) antagonist, o n the plasma concentrations of prolactin in overtly pseudopregnant Afghan h ounds and on the clinical symptoms of overt pseudopregnancy were studied. P lasma concentrations of prolactin and progesterone were determined in six A fghan hounds with signs of overt pseudopregnancy for 2-3 weeks and in three Afghan hounds that were not pseudopregnant at the itme of blood sampling. In the overtly pseudopregnant bitches the plasma concentrations of prolacti n before treatment (35,5 +/- 8,5 mu g l(-1)) were significantly higher than the plasma concentrations of prolactin of the three bitches that were not pseudopregnant (6,3 +/- 0,5 mu g l(-1)); the latter values were similar to those of non-pseudopregnant beagle bitches during the total luteal phase. T he six pseudopregnant Afghan hounds were treated for 10 days with the antis erotoninergic drug metergoline. At 2 h after the onset of treatment with me terogline, the mean plasma concentration of prolactin had decreased to 10,8 +/- 2,9 mu g l(-1). The plasma concentrations of prolactin continued to de cline to 5,4 +/- 1,0 mu g l(-1) at 4 h and to 1,0 +/- 0,1 mu g l(-1) during treatment days 3-10. Signs of pseudopregnancy, such as swelling of the mam mary glands and digging, decreased during the treatment period. The treatme nt was associated with mild behavourial side effects such as whimpering and aggressiveness. These side effects are probably not related to suppression of prolactin but are due to a direct effect on serotoninergic pathways in the brain. It is concluded that high plasma concentrations of prolactin are associated with the development and maintenance of pseudopregnancy. The se rotonin antagonist metergoline strongly suppresses plasma concentration of prolactine in pseudopregnant dogs and decreases the clinical signs of pseud opregnancy.