Effect of estradiol and progesterone on myometrial LH/hCG receptors in pigs

Abstract

High affinity luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptors have been identified in porcine, rabbit and rat uteri and immunocytochemically demonstrated in the human uterus. We have now assessed the effect of estradiol and progesterone on the capacity and affinity of LH/hCG binding sites in crude membrane fractions of porcine myometria. Nineteen cross-bred gilts were ovariectomized at 6–7 months of age. Five weeks later, the experiment was conducted and gilts were given estradiol benzoate 2 mg (N= 5), progesterone 50mg (N=4) and 2 mg of estradiol benzoate plus 50 mg of progesterone in 2 ml of corn oil (N = 6), im for five consecutive days. Controls (N = 4) received 2 ml of the vehicle. Gilts were hysterectomized 24 h after the last injection. Blood samples for assays of LH, estradiol and progesterone were collected 1 h before hysterectomy. The numbers and affinities of unoccupied LH/hCG binding sites were characterized in all samples of myometrium. The results indicate that treatment with estradiol benzoate increases (p <0.01) the number of LH/hCG binding sites compared with gilts receiving corn oil. Progesterone treatment caused elevation in the number of LH/hCG receptors (p<0.05), when compared with estradiol alone (2.9±0.3 vs 1.2±0.1 fmol/mg protein, respectively). Combined administration of estradiol and progesterone increased receptor capacity to 2.7±0.4. Steroid treatment did not alter the affinity (Ka) of [125I]hCG binding to receptors and it varied from 1.8±0.8 to 2.9±0.2 ×1011 l/mol. Concentrations of LH (pmol/l) were maintained at high (64.3±14.3), medium (28.6±10.7), and low (10.7±3.6) levels in control, progesterone and both estradiol and estradiol plus progesterone treated groups, respectively. These results indicate that estradiol and progesterone independently stimulate the appearance of unoccupied LH/hCG receptors in the porcine myometrium.

Conceptus signals for establishment and maintenance of pregnancy

“…PGF from the uterus is taken up by the mesometrium and transferred to the ovary in arterial blood by a countercurrent system that exists in the broad ligament of the uterus [112]. Estrogen also changes the ratio of PGE:PGF [113][114][115] as well as maintains LH receptor levels in both CL and uterus [116,117]. PGE 2 may protect the CL from the luteolytic effects of PGF.…”

Stimulation of pregnenolone metabolism and aromatase activity by luteinizing hormone in mouse uterus

“…The concentrations of uterine receptors fluctuate with the stages of reproduction. The amounts of receptors in porcine uterine tissue are higher during the luteal phase and in early pregnancy than in follicular phase of the estrous cycle (1,12,13). In the mouse uterus, the amounts are high during the late-diestrous stage (9), whereas in rat uterus, this occurs during the metestrous stage (14).…”

Expression of functional follicle-stimulating hormone receptor and luteinizing hormone/chorionic gonadotrophin receptor in oviduct and uterus in prepubertal gilts

“…In the estrous pigs, the expression of LH/CGR was found in the endometrial epithelium and stromal cells, as well as the myometrial smooth muscle and vascular smooth muscle (Ziecik et al, 1992). Unlike LH/CGR, the functional role of uterus FSHR is unclear.…”