Sodium cloprostenol administered at a continuous low dosage induces polydipsia and suppresses luteal function in early dioestrous bitches

The aim of this study was to determine whether sodium cloprostenol administered at a continuous low dosage induced luteolysis and polydipsia in early dioestrous bitches. Sodium cloprostenol was administered subcutaneously to greyhounds at doses of 4.04–5.19 μg/kg/day (treated group, n=5) or 0 μg/kg/day (control group, n=5) delivered by mini-osmotic pumps for 7 days. The treated bitches and two of the control bitches were in early dioestrus (Days 5–14, and 6 and 10, respectively) when the mini-osmotic pump was inserted (Day 0). Concentrations of plasmatic progesterone were measured in dioestrous bitches each day from Day −2 to 7, and then weekly until Day 90. Daily intake of water was ascertained in all bitches from Day −2 until Day 10, and their weight was measured on Days −2, 6 and 13. Biochemical analyses on plasma for concentrations of urea and glucose, and urinalyses were performed on all bitches before (Day −1), during (Day 4) and after treatment (Day 10). Concentrations of plasmatic progesterone declined dramatically and rapidly in treated bitches after Day 0 to <2.9 ng/ml but were not similarly affected in the dioestrous control bitches. However, in three of five treated bitches, concentrations of plasmatic progesterone increased to >1 ng/ml in the period from Day 10 to 90 indicating that luteolysis was incomplete. All treated bitches were polydipsic (intake of water >100 ml/kg/day) for 2–6 days during the period of treatment, and for 0–2 days immediately after treatment (Days 7 and 8). One control bitch was polydipsic on Days −2, −1 and 0. The treated bitches were also polyuric since they were hyposthenuric (<1.007, n=4) or isothenuric (1.010, n=1) on Day 4, their weight did not increase and no gastrointestinal or respiratory effects were observed. The control bitches were always hypersthenuric when measured during and after treatment (>1.021). Biochemical analyses of plasma and other data obtained from urinalyses did not reveal any differences between groups. This study indicated that sodium cloprostenol administered at a continuous low dosage induced polydipsia and suppressed luteal function in early dioestrous bitches.