Follicular development and plasma concentrations of LH and prolactin in anestrous female dogs treated with the dopamine agonist cabergoline

The effect of a daily administration of a dopamine agonist (cabergoline, 5 μg/kg) for 4 weeks, starting about 95 days after the end of estrus on follicular development and its relationship with LH and prolactin secretion has been investigated in two groups of anestrous bitches (Beagles and Greyhounds). Pro-estrus was detected in 80% (8/10) of beagles and 50% (3/6) of treated greyhounds. The mean inter-estrus interval of treated animals was 132 ± 5.0 and 169 ± 7.0 days for beagles and greyhounds, respectively, and in both this differed significantly from the cycle preceding treatment (192 ± 9.0 and 198 ± 12.0 days) and from that in untreated bitches (194 ± 11.0 and 196 ± 11.0 days for beagles and greyhounds, respectively (all comparisons at P < 0.001). The interval from the beginning of treatment to pro-estrus in responding animals was 13.3 ± 1.90 days in beagles and 20.3 ± 1.70 days in greyhounds. Cabergoline increased (P < 0.001) the length of pro-estrus (10.6 ± 0.50 and 11.7 ± 0.50 days) in the treated estrus cycle compared to the previous estrus cycle (8.4 ± 0.30 and 8.8 ± 0.40 days for in beagles and greyhound, respectively). Ovarian enlargement and follicle development was detected by ultrasound in 90% of treated beagles and in 83% of greyhound between the second and third weeks of treatment, but only 80% of beagles and 66% of treated greyhound displayed pro-estrus and estrus. In the treated bitches, mean plasma LH increased (P < 0.001) before pro-estrus. There was high variability in mean plasma prolactin levels between animals.These data indicate that the administration of the dopamine agonist cabergoline to anestrous bitches increases mean LH plasma levels and induces follicular development shortly before pro-estrus but this activity is not always followed by pro-estrus and estrus. Finally, prolactin per se does not have a prominent role in the control of folliculogenesis in the bitch.