Effect of divergent selection for uterine capacity on progesterone, estradiol and cholesterol levels around implantation time in rabbits.

Abstract

The effects of selection for high (H) and low (L) uterine capacity on serum and uterine fluid levels of progesterone and serum levels of estradiol and cholesterol, near implantation (day 6 of gestation), were studied. Both lines had similar ovulation rates (15.2 vs 14.4), but different number of embryos (12.8 vs 11.0; P<0.05) for H and L, respectively. Progesterone, cholesterol and estradiol were similar in both lines (9.3 and 9.6 ng/ml serum progesterone; 15.6 and 13. 7 ng/ml of uterine fluid progesterone; 28.1 and 27.6 pg/ml of estradiol; and 66.6 and 68.0 mg/dl of cholesterol for H and L, respectively). Lactation strongly affected the variables studied. Lactating does had higher ovulation rates than non-lactating (15.6 vs 14.0; P<0.05), but no differences were detected for the number of embryos recovered (12.2 and 11.6 for lactating and non-lactating, respectively) or for embryo survival (0. 79 and 0.84 for lactating and non-lactating). L does had lower levels of serum progesterone (8.7 ng/ml), uterine fluid progesterone (13.0 ng/ml) and serum cholesterol (59.3 mg/dl) than non-lactating females (10.2 ng/ml, 16.3 ng/ml and 75.3 mg/dl respectively; P<0.05). Lactation did not affect serum levels of estradiol. Serum progesterone levels were slightly correlated with ovulation rate (r=0.24; P<0.05). Ovulation rate and number of embryos recovered were correlated with progesterone uterine fluid in lactating females (r=0.55 and 0.49 respectively; P<0.05). Embryo survival in lactating females was negatively correlated with the concentration of estradiol (r=-0.39; P<0.05).