Immunohistochemical Studies on Oestrogen Receptor Alpha (ERα) and the Proliferative Marker Ki‐67 in the Sow Uterus at Oestrus and Early Pregnancy

Abstract

Oestrogen receptor alpha (ERalpha), the main subtype in the uterus, is involved in the regulation of uterine growth/proliferation. A relationship between ERalpha and proliferative activity has been shown in the cyclic sow uterus, but to our knowledge, no study has been carried out on early pregnant sows. Therefore, by means of immunohistochemistry and use of mouse monoclonal antibodies to ERalpha and a proliferative marker, Ki-67, the localization of these proteins was investigated in the sow uterus during early pregnancy. Eighteen crossbred multiparous sows were artificially inseminated once at 20-15 h before expected ovulation. After artificial insemination (AI), they were slaughtered at five different times: at oestrus, 5-6 h after AI (n = 4), 20-25 h after ovulation (n =4), 70 h after ovulation (n = 4), on day 11 (the first day of standing oestrus = day 1, n = 3) and on day 19 (n = 3). Immediately after slaughter, uterine samples were collected at the mesometrial side of the uteri, fixed in 10% formaldehyde and embedded in paraffin. Immunohistochemistry was performed by using mouse monoclonal antibodies to ERalpha (C-311) and Ki-67 (MM1). All sows slaughtered after ovulation were pregnant. In general, positive immunostaining for ERalpha and Ki-67 was found in the nuclei. Variations in staining intensity and proportion of positive nuclei were observed in different uterine compartments and stages of early pregnancy. The highest level of ERalpha presence in the surface epithelium and myometrium was found at oestrus (5-6 h after AI), and low levels of ERalpha in these compartments were observed as early as 20-25 h after ovulation. In the glandular epithelia, presence of ERalpha was highest at 70 h after ovulation. The largest number of ERalpha-positive cells in the stroma was observed at oestrus and early after ovulation. Low proliferation was observed, and with no significant difference in tissue compartments except in the glandular epithelium. High proliferative activity in the glandular epithelium at 70 h after ovulation indicated involvement in preparation for secretory activity and growth during pregnancy establishment. Significant positive correlation was found between the number of ERalpha-positive cells in the stroma and Ki-67-positive cells in the surface epithelium. In conclusion, the present study showed differences in immunolocalization of ERalpha and the proliferative marker Ki-67 in different tissue compartments of the sow uterus at oestrus and early pregnancy. In some uterine compartments, the patterns of ERalpha and Ki-67 immunostaining seemed to be influenced by insemination and the presence of embryos, in addition to the effects of steroid hormones.

Immunohistochemical studies on the progesterone receptor (PR) in the sow uterus during the oestrous cycle and in inseminated sows at oestrus and early pregnancy

“…As PR is generally upregulated by oestrogens, the lack of high PR levels in the surface epithelium at prooestrus indicates a delayed effect, possibly via ERa in the stroma as will be discussed below. This is supported by our previous studies (Sukjumlong et al 2003(Sukjumlong et al , 2004b showing that stromal ERa was high at prooestrus. At later stages (dioestrus, and late dioestrus/d 11 and d 19), the PR levels in the surface epithelium of the present study were low.…”

“…The localization of steroid receptors can differ among specific tissue compartments of the uterus, even at the same plasma steroid level. This has been shown for PR in different species (Lessey et al 1988, Ohta et al 1993, Wathes & Hamon 1993, Geisert et al 1994, Dhaliwal et al 1997 as well as for ERa in our previous studies on both cyclic and inseminated/early pregnant sow uteri (Sukjumlong et al 2003(Sukjumlong et al , 2004b.…”

“…The glandular epithelium can be further divided into functional units as the present study showed that the levels of PRpositive cells differed between superficial and deep layers which is in agreement with other PR studies in ewes (Spencer & Bazer 1995) and bitches (Vermeirsch et al 2000) as well as our earlier studies on ERa using the same sows. (Sukjumlong et al 2003(Sukjumlong et al , 2004b. This indicates different roles or functions for glandular levels under the same steroid hormone regulation.…”

“…Our previous studies on oestrogen receptor alpha (ERa) and proliferative activities in the sow uterus revealed that ERa may be related to proliferation in the epithelia (Sukjumlong et al 2003(Sukjumlong et al , 2004b. However, physiological changes in the uterus should involve regulation via PR as well.…”

Histological changes within ovarian cortex, oviductal and uterine mucosa in case of ovarian cysts presence in sows.

“…The high proliferative rate of uterine glands can be explained as a preparation for secretory activity and growth during pregnancy establishment. The endometrium shall create an appropriate environment for the growing embryos [9]. One reason for very early embryonic death is non-parallel development of conceptuses and endometrium [5].…”