Dioestrous ovariectomy: a model to study the role of progesterone in the onset of canine pseudopregnancy.
It has been suggested that overt pseudopregnancy in bitches is caused by an increase in the concentration of serum prolactin as a result of an abrupt decrease in progesterone concentration in the late luteal phase. This hypothesis was tested by using ovariectomy at dioestrus as an experimental model. A total of 18 intact cross- and purebred bitches were used. Eleven animals were ovariectomized (day 0) between day 25 and day 40 of the oestrous cycle, and seven intact bitches were used as controls. Blood samples for determination of prolactin and progesterone concentrations were collected on days -1, 1, 2, 3 and 7 in the ovariectomized group, and on day 1 and day 7 in the control group. On day 7, the presence or absence of overt pseudopregnancy was recorded. The four ovariectomized bitches with a history of pseudopregnancy showed signs of overt pseudopregnancy (P < 0.01). On day 7, progesterone concentrations were significantly higher in the control than in the ovariectomized bitches (P < 0.01). The expected decrease in serum progesterone concentration after ovariectomy was similar in pseudopregnant bitches and non-pseudopregnant bitches. However, in pseudopregnant bitches, but not in non-pseudopregnant bitches, there was a marked increase (expressed as percentage change) in the concentration of prolactin between day -1 and day 7 (P < 0.01). It was concluded that the abrupt decrease in progesterone concentrations does not lead systematically to pseudopregnancy. Only in bitches predisposed to pseudopregnancy would an abrupt decrease in progesterone concentrations induce a substantial increase in prolactin concentrations, which in turn would trigger the typical signs of pseudopregnancy.
Gobello
C
C
Institute of Theriogenology, Faculty of Veterinary Sciences, National University of La Plata 60 y 120, La Plata (1900) Argentina.
Baschar
H
H
Castex
G
G
de la Sota
R L
RL
Goya
R G
RG
D000818:Animals; D004031:Diestrus; D004283:Dog Diseases; D004285:Dogs; D005260:Female; D008954:Models, Biological; D010052:Ovariectomy; D011374:Progesterone / Q000097:blood; D011388:Prolactin / Q000097:blood; D011555:Pseudopregnancy
D011374:Progesterone; D011388:Prolactin