Differential luteolytic effects of right and left uterine horns in the alpaca

The effect of the uterus on corpus luteum function was studied in adult multiparous alpacas subjected to different surgical treatments. Removal of the left uterine horn from females with a corpus luteum in the left ovary significantly prolonged luteal function in 3 out of 4 females, as evidenced by high peripheral plasma progesterone levels, large corpora lutea and lack of sexual receptivity. Removal of the right uterine horn in females with a corpus luteum in the right ovary also prolonged luteal function, but the effect in this case was much less marked. Only 1 animal, out of a total of 4, maintained a large and functional corpus luteum up to Day 70 and she rejected the male at all times. Removal of the oviduct ipsilateral to the ovary containing the corpus luteum or the contralateral uterine horn and oviduct, had no effect on the lifespan of the corpus luteum, regardless of whether this was located in the right or the left ovary; early regression of the corpus luteum, as indicated by a marked decline in plasma progesterone levels by Day 12 and sexual receptivity occurred in all of these animals. These results were similar to those of the control, sham operated females. In females with a corpus luteum in each ovary results were as follows: a) removal of both uterine horns and oviducts caused maintenance of both corpora lutea up to Day 70; b) removal of the left uterine horn and oviduct prolonged the lifespan of the corpus luteum in the left ovary, but the one in the right ovary showed early regression; c) removal of the right uterine horn and oviduct failed to exert any effect on the corpora lutea as evidenced by early regression of both. Results indicate that the luteolytic activity of the right uterine horn in the alpaca is local only, while that of the left uterine horn, has both a local effect and a systemic effect.