Progesterone, oestradiol, FSH and LH concentrations in serum of progesterone-treated pregnant bitches with suspected luteal insufficiency.

In the bitch, the corpus luteum is the only source of circulating progesterone throughout pregnancy. Inadequate luteal function may be a cause of abortion or foetal resorption observed after early pregnancy diagnosis. In our study of factors involved in canine luteal inadequacy, 35 pregnant bitches from different breeds were allocated to groups of healthy control (n = 15) vs hypoluteoid (n = 20) pregnant bitches, based on presence or absence of clinical signs of impending abortion and on progesterone concentrations below 10 ng/ml at the 4th-5th week of pregnancy. Hypoluteoid bitches were treated daily with 10-mg natural progesterone in injectable form (Luteosan inj.; Alvetra and Werfft AG, Vienna, Austria) until day 60. Serum progesterone, 17beta-oestradiol, FSH and LH concentrations were measured in samples obtained weekly using ELISA previously validated for dog serum. The exogenous progesterone supplementation was presumed to be sufficient to prevent foetal loss in 15 of the 20 treated bitches. The mean serum progesterone concentration in control pregnant bitches did not decrease below 10 ng/ml until the 8th week of pregnancy. Progesterone concentrations in progesterone-treated hypoluteoid bitches at week 4 were lower than in controls (p < 0.05), but although numerically higher did not differ significantly from those of controls during the period of treatment. Serum 17beta-oestradiol concentrations of healthy bitches were variable, were at most time higher than those of treated animals and slowly decreased until parturition; those of treated bitches remained unchanged during the study. Serum FSH and LH concentrations did not differ between groups. Additional studies involving untreated pregnancies showing equivalent evidence of hypoluteoidism as well as assay of circulating relaxin and prolactin in treated and untreated bitches are needed to better determine the causes and effects of hypoluteoidism in pregnant bitches.