Immunolocalization, binding, and biological activity of endothelin in rabbit uterus: effect of ovarian steroids.
Specific immunostaining for endothelin 1 (ET-1) was observed in the endometrium but not myometrium of rabbits. The staining was dramatically affected by subacute treatment with ovarian steroids: epithelial cells were predominantly positive in immature rabbits, whereas, in sex steroid-primed rabbits, ET-1 was mainly localized in the stromal compartment. Binding studies were performed in myometrium of estrogen-treated rabbits using labeled ET-1 and ET-3, the corresponding unlabeled peptides, and sarafotoxin b (SRTX). Mathematical modeling of experimental results indicates that two populations of sites are present in myometrium. One site (R1 = 1 pmol/mg protein) shows approximately the same affinity for ET-1, ET-3, and SRTX [dissociation constant (Kd) 100 pM], whereas the second site (R2 = 10 pmol/mg protein) selectively binds ET-1 (Kd 400 pM). According to binding studies, ET-1 was more potent than SRTX in stimulating uterine contraction "in vitro." The subacute administration of increasing concentrations of 17 beta-estradiol (0.2-200 micrograms/kg for 4 days), but not 17 beta-estradiol (200 micrograms/kg for 4 days) plus progesterone (5 mg/kg for 4 days), stimulates a dose-dependent increase in endothelin receptors in myometrium (half-maximal effective dose = 0.7 micrograms/kg for 4 days). However, estrogen treatment does not affect the concentration of endothelin receptors in myometrial cells in primary culture. Conversely, divalent ions like calcium and magnesium enhance the binding of ET-1 to both uterine membranes and cells. Our results indicate that in rabbit uterus endothelin is present in the endometrium, whereas specific receptors are located in myometrium.
Maggi
M
M
Department of Clinical Physiopathology, University of Florence, Italy.
Vannelli
G B
GB
Peri
A
A
Brandi
M L
ML
Fantoni
G
G
Giannini
S
S
Torrisi
C
C
Guardabasso
V
V
Barni
T
T
Toscano
V
V
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004533:Egtazic Acid / Q000494:pharmacology; D004717:Endometrium / Q000166:cytology*; D016232:Endothelins / Q000032:analysis* / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007124:Immunoenzyme Techniques; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009215:Myometrium / Q000166:cytology* / Q000378:metabolism; D011374:Progesterone / Q000494:pharmacology*; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000378:metabolism; D017466:Receptors, Endothelin; D012016:Reference Values; D014590:Uterine Contraction / Q000187:drug effects*; D014599:Uterus / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism
D016232:Endothelins; D011956:Receptors, Cell Surface; D017466:Receptors, Endothelin; D011374:Progesterone; D004958:Estradiol; D004533:Egtazic Acid; D008274:Magnesium; D002118:Calcium