Study of the change of prolactin and progesterone during dopaminergic agonist treatments in pseudopregnant bitches

In order to clarify the role of prolactin (PRL) and progesterone (P-4) in t he pathophysiology of canine pseudopregnancy (PSP) we designed an experimen t, where we induced an abrupt pharmacological blockade of PRL secretion wit h dopaminergic agonists (DA) or placebo (PL). Thirty overtly pseudopregnant (PSPT) bitches were randomly allocated to three groups of 10 animals each: FL. bromocriptine (BR), and cabergoline (CA), which were treated with FL, 7.5 mug/kg BR and 5 mug/kg CA, respectively. On days 1, 7 and 1 1 (day a: b eginning of the treatment) all the animals were classified into grades of i ntensity of PSP clinical signs, considering serum or milk secretion and enl argement of the mammary glands. Presence or absence of treatment side effec ts were recorded and blood samples for PRL and Pq determinations collected. Serum PRL and P-4 concentrations (ng/ml) of all the animals on day 1 were (least squares means [LSM] +/- S.E.M.) 17.70 +/- 2.05 and 1.13 +/- 0.13, re spectively. During the experiment, serum PRL and P-4 concentrations decreas ed (day effect., P < 0.05). During the experiment, serum PRL concentrations were lower in the DA treated group (BR and CA) compared with PL group (P < 0.05), After a week of treatment, the percentage change of PRL was -62.52 Versus 102.16 +/- 46.20 (P < 0.01) for the treated (BR and CA) and PL group s, respectively. Conversely, no significant differences were found in the p ercent change in PRL between the BR and the CA groups nor in P? percentage change among all groups for the same week. Significant differences in the a chievement of complete remission between treated and PL groups were found o n days 7 (40 versus 0%, P < 0.05) and 14 (90 versus 0%, P < 0.01), Nu signi ficant correlation between PBL and P-4 was found on day I in any of the ani mals. However, a significant correlation for the same hormones was found on days 7 and 14 for the DA treated groups (r = 0.46, P < 0.01). While in the PL group, PRL concentrations and intensity of clinical signs were not sign ificantly correlated on days 1, 7 and 14, in the DA treated groups they wer e significantly correlated on days 7 and 14 (r = 0.34, P < 0.05). The prese nce of a positive correlation between PRL concentrations and the grades of intensity of clinical si ns in the treated animals indicates the major role Of PRL. in PSP physiopathology. However the lack of correlation during spo ntaneous involution of PSP in the PL group demonstrates that PRL concentrat ions do not completely explain the problem. In summary. abrupt changes in s erum PRL seemed to be more important in ceasing PSP signs than total PRL co ncentrations in these groups of animals. (C) 2001 Published by Elsevier Sci ence B.V.