Progesterone-Binding Proteins From Endometrium and Myometrium of Sheep Uterus: A Comparative Study

Abstract

The binding of tritiated progesterone to the cytoplasmic progestogen receptors from oestrogen-primed sheep endometrium and myometrium has been investigated. The binding characteristics of the progesterone receptors from both sources were determined in the supernatant fractions obtained after high speed centrifugation of the myometrial and endometrial homogenates. High affinity binding proteins with identical association constants for progesterone (1 \m=x\ 109 m\m=-\1) were detected in both endometrium and myometrium. The concentration of binding sites was also of the same order of magnitude in both tissues. After centrifugation on sucrose gradients, these binding proteins were shown to have similar sedimentation constants, 7 S in a gradient containing no added KC1 and 4 S in a gradient containing 0.4 m KCI. The binding peaks from both sources could be abolished by heating the cytosol at 60\s=deg\Cfor half an hour. The proteinaceous nature of the binding materials was demonstrated by incubation of the endometrial and myometrial cytosols with pronase, DNase and RNase: the binding was totally eliminated by the proteolytic action of pronase whereas DNase and RNase had no effect.The ligand specificity of the two progesterone binding proteins was studied using a competitive protein-binding technique. Both the endometrial and the myometrial receptor proteins were shown to bind only steroids which are known potent progestogens. In addition, the relative affinities of the binding proteins for 37 steroidal compounds closely resembled each other. Thus, the physicochemical and binding data obtained show that a very close similarity exists between the progesterone-binding proteins in the endometrium and myometrium of ovariectomized sheep after oestradiol treatment.

Hormone Receptor Levels and Hormone, Rna and Protein Metabolism in the Genital Tract During the Oestrous Cycle of the Ewe

“…Thus, in the ewe, it seems likely that within each receptor type the mean cell content at each stage of the cycle examined is very similar in stromal and myometrial cells, the principal cell types in endometrium and myometrium (Asdell, 1965). For the progesterone receptor in the ewe, a similar concentration in endometrium and myometrium has been reported (Kontula, 1975). The ewe would appear to differ from a species such as the rat where the concentration of at least the oestradiol receptor is considerably higher in endo¬ metrium than in myometrium (Feherty, Robertson, Waynforth & Kellie, 1970;Mester, Martel, Psychoyos & Baulieu, 1974).…”

Oestrogen‐Insensitive Progestin Receptors in the Central Nervous System: Physicochemical and Immunoreactive Characteristics

“…6~. It was noted that the sedimenting cerebellum PR area (fractions [15][16][17][18][19][20][21][22] was small due to the low receptor content in this Aliquots of cerebral cortex nuclei were incubated with labelled cytosol PR from cerebral cortex (Ctx C) and UC (B). Incubations were carried out at 22 "C for 60 min.…”

“…The study was supported by CONACYT and the University Programme of Research in Health (PUIS, UNAM) (Mexico), CNRS (France), and The Rockefeller Foundation (USA). A portion of this study was presented at the XIX Conference on Reproductive Behaviour, Tlaxcdla, Mexico, June [14][15][16][17] 1987. M. M. is a postdoctoral Fellow in Reproductive Biology under the support of a CONACYT award for foreign students.…”

Antiprogestins

“…In many species (mouse, rat, guinea pig, hamster, sheep, calf, and human), highaffinity receptors for progesterone have been identified in the uterine cytosol (Milgrom and Baulieu 1970 a;McGuire and De Della 1971;Thomas 1973;Leavitt et al 1974;Gueriguian et al 1974;Kontula 1975b). The complex steroid and receptor is heat and acid labile (Janne et al 1975), and the binding activity of progesterone to its receptor can be inhibited by sulfhydryl-blocking agents, indicating that SH groups are involved in the formation of the steroid-receptor complex (Kontula et al 1974a;Janne et al 1975).…”

“…Similarly, the myometrial and endometrial progesterone receptors are thought to be very similar in such species as guinea pig, human, and sheep (Janne et al 1975;Luu Thi et lll. 1975;Kontula 1975b). …”