The Lack of Relationship between Progesterone Level in Utero-Ovarian Vein and the Number of Corpora Lutea in the Pigs1)

Ovine endometrial estrogen receptor expression is altered following PG-600 administration

BACKGROUND

Dysregulation of the estrogen receptor 1 (ESR1) expression during the establishment of pregnancy could contribute to reduce fertility reported in ewes treated with PG-600.

OBJECTIVES

The objective of this study was to evaluate the effect of treatment with PG-600 on ESR1 expression in the ovine endometrium during early diestrus.

METHODS

Polypay ewes (n = 24) that had exhibited an oestrous cycle of normal duration (16-18 days) were treated with intravaginal progesterone-releasing device (CIDR) for 9 days. Cloprostenol was administrated two days before CIDR withdrawal. On the day of CIDR withdrawal (day 0), ewes received a 5 mL intramuscular injection of PG-600 (400 IU equine chorionic gonadotropin and 200 IU human chorionic gonadotropin) or saline. Blood samples were collected before treatment and on the day of tissue collection to determine serum estradiol-17β and progesterone concentrations using radioimmunoassay. On days 4 and 7, six ewes from each treatment group were anaesthetised and a laparotomy was performed to obtain intercaruncular endometrial samples. Endometrial samples were collected ipsilateral to the ovary bearing the highest number of corpora lutea. An estradiol exchange assay was used to determine ESR1 concentration.

RESULTS

Estradiol concentrations did not differ by time or treatment, but progesterone concentrations were significantly higher in the PG-600-treated group on day 7 despite a similar number of corpora lutea. Endometrial ESR1 concentration was significantly reduced on day 7 in the PG-600 group.

CONCLUSIONS

In conclusion, although progesterone was higher than controls on day 7, ESR1 did not differ from controls suggesting that treatment with PG600 is unlikely to impair reproductive potential.

The persistence of the corpus luteum of pregnancy into lactation in the marsupial bandicoot, Isoodon macrourus

The bandicoot is unique among marsupials in possessing a corpus luteum of pregnancy which continues to secrete progesterone during lactation. Different factors which may influence the activity of this corpus luteum were examined. There was no correlation between the number of pouch young and the plasma progesterone concentration. Similarly, bromocriptine did not appear to cause a dramatic decrease in plasma progesterone early in lactation, however, it may induce premature regression of the corpus luteum late in lactation. Corpora lutea were not observed in the ovaries of two out of six bandicoots treated with bromocriptine late in lactation. Although the corpus luteum may influence ovarian activity early in lactation, and corpus luteum does not appear to influence reproduction late in lactation. Removal of corpora lutea at Day 30 of lactation caused an abrupt decline in plasma progesterone; however, the birth of the subsequent litter occurred on Days 58 and 61 (N = 2), births normally occurring on Day 60.