Growth hormone receptor gene expression in the mouse uterus: modulation by gonadal steroids

We hypothesized that the mouse uterus expresses a growth hormone receptor (GHR) and that mouse endometrial GHR mRNA may undergo in vivo regulation by estradiol (E2) and progesterone (P).

Two weeks after bilateral ovariectomy, 35-day-old Balb/c mice were randomly assigned to receive either vehicle injections; E2 priming (300 ng/day) on days 1-6 and E2 (50 ng/day) on day 11; P (1 mg/day) on day 8-11; or E2 priming with P (days 8-11) and E2 on day 11, with or without RU 486 on day 8-11. At sacrifice 24 hours after the last injection, the uteri were processed for RNA extraction and in situ hybridization for GHR mRNA. Reverse transcriptase polymerase chain reaction amplification of uterine mRNA was performed to establish whether treatment with gonadal steroids differentially affected GHR gene expression. The GHR primers flanked a 326-bp region from the intracellular domain sharing no homology to the prolactin receptor or to the GH-binding protein. A 48-bp digoxigenin-labeled oligoprobe was used for in situ hybridization.

Densitometry analysis of polymerase chain reaction products from total uterine mRNA revealed similar GHR mRNA expression in vehicle- and estrogen-treated animals. The addition of progesterone reduced GHR mRNA expression. In situ hybridization localized the GHR mRNA to the endometrium, glands, stroma, and myometrium. Stromal staining was reduced in the progesterone-treated mice.

The identification of GHR message suggests that the mouse uterus is a site of action of GH. The lack of modulation of epithelial GHR by sex steroids does not support a role of GHR in this compartment.