In the uterus, estrogen causes a rapid increase in microvascular permeability, followed later by growth of the endometrium, including the richly vascular stroma. Vascular endothelial growth factor/vascular permeability factor (VEGF/VPF or VEG/PF) is an angiogenic protein that is not only a specific mitogen for endothelial cells, but also a potent stimulator of microvascular permeability. Because of these properties, it seems likely that VEG/PF might mediate estrogen-induced increases in uterine vascular permeability and blood vessel growth. Therefore, we determined whether the gene for VEG/PF is expressed in the rat uterus and if mRNA abundance is regulated by steroid hormones, using reverse transcription-polymerase chain reaction. The VEG/PF gene is alternatively spliced and gives rise to three transcripts coding for proteins of 188, 164, and 120 amino acids, which, in turn, form the active dimeric factors. Transcripts for VEG/PF mRNAs were detected in the uterus of the rat by reverse transcription-polymerase chain reaction. The mRNAs for the VEG/PF164 and VEG/PF120 subunits were the dominant forms expressed. Treatment with both estradiol (E2) and estriol (E3) rapidly induced an increase in the level of the two smaller transcripts. The increase was detectable as early as 0.5-1 h and peaked at 2 h. Levels of the two smaller transcripts then declined, but remained above control levels for 24 h. The degree of stimulation of VEG/PF mRNA levels was 8-fold at 2 h. VEG/PF188 mRNA levels were higher by 6 h compared to control values. The increase in VEG/PF mRNA levels in response to E2 was not contingent upon de novo protein synthesis, as it was not blocked by cycloheximide. The increase occurred as rapidly as that of the mRNA for Zif268, an estrogen-induced transcription factor. Progesterone also stimulated the expression (at 6 h) of VEG/PF164 and VEG/PF120, but not that of VEG/PF188. We conclude that the VEG/PF gene is expressed in the rat uterus, and that mRNA levels are rapidly enhanced by estrogen. This response suggests that VEG/PF may be involved in the estrogen-induced increase in permeability and proliferation of uterine blood vessels. The identification of VEG/PF as a primary response gene also suggests that VEG/PF expression may be a prerequisite for the subsequent expression or action of other growth factors in the uterus.
In the uterus, estrogen causes a rapid increase in microvascular permeability, followed later by growth of the endometrium, including the richly vascular stroma. Vascular endothelial growth factor/vascular permeability factor (VEGF/VPF or VEG/PF) is an angiogenic protein that is not only a specific mitogen for endothelial cells, but also a potent stimulator of microvascular permeability. Because of these properties, it seems likely that VEG/PF might mediate estrogen-induced increases in uterine vascular permeability and blood vessel growth. Therefore, we determined whether the gene for VEG/PF is expressed in the rat uterus and if mRNA abundance is regulated by steroid hormones, using reverse transcription-polymerase chain reaction. The VEG/PF gene is alternatively spliced and gives rise to three transcripts coding for proteins of 188, 164, and 120 amino acids, which, in turn, form the active dimeric factors. Transcripts for VEG/PF mRNAs were detected in the uterus of the rat by reverse transcription-polymerase chain reaction. The mRNAs for the VEG/PF164 and VEG/PF120 subunits were the dominant forms expressed. Treatment with both estradiol (E2) and estriol (E3) rapidly induced an increase in the level of the two smaller transcripts. The increase was detectable as early as 0.5-1 h and peaked at 2 h. Levels of the two smaller transcripts then declined, but remained above control levels for 24 h. The degree of stimulation of VEG/PF mRNA levels was 8-fold at 2 h. VEG/PF188 mRNA levels were higher by 6 h compared to control values. The increase in VEG/PF mRNA levels in response to E2 was not contingent upon de novo protein synthesis, as it was not blocked by cycloheximide. The increase occurred as rapidly as that of the mRNA for Zif268, an estrogen-induced transcription factor. Progesterone also stimulated the expression (at 6 h) of VEG/PF164 and VEG/PF120, but not that of VEG/PF188. We conclude that the VEG/PF gene is expressed in the rat uterus, and that mRNA levels are rapidly enhanced by estrogen. This response suggests that VEG/PF may be involved in the estrogen-induced increase in permeability and proliferation of uterine blood vessels. The identification of VEG/PF as a primary response gene also suggests that VEG/PF expression may be a prerequisite for the subsequent expression or action of other growth factors in the uterus.
Previous studies established that in the rat, the uterus can accept a developing blastocyst for implantation only during a limited period of time on day 5 of gestation, termed the receptive phase. Our previous studies showed that the expression of calcitonin, a peptide hormone that regulates calcium homeostasis, is induced in rat uterus between days 3-5 of gestation and is switched off once the implantation process has progressed to day 6. In the present study, we analyze in detail how the expression of calcitonin messenger RNA (mRNA) in the uterus is regulated by the steroid hormones progesterone and estrogen and explore the possibility that calcitonin may serve as a potential marker of uterine receptivity. We demonstrate by in situ hybridization that calcitonin mRNA is synthesized specifically in the glandular epithelial cells between days 3-5 of pregnancy. Interestingly, calcitonin synthesis is also induced in these cells during pseudopregnancy, indicating that this peptide hormone is produced in the endometrium in response to maternal, rather than embryonic, signals. We also demonstrate that calcitonin mRNA expression during pseudopregnancy, like that in normal pregnancy, is under progesterone regulation. We further examined the steroid hormone regulation of uterine calcitonin expression in a delayed implantation model. In pregnant rats in which implantation is blocked upon removal of both ovaries on day 4 of gestation, continued administration of progesterone sustains calcitonin expression in the uterus for several days in the absence of estrogen. Administration of estrogen, which allows delayed implantation, also rapidly reduces calcitonin expression, indicating a role for this steroid hormone in turning off calcitonin gene expression. In gene transfection studies, expression of the progesterone receptor B isoform in cultured endometrial cells induces RNA synthesis from a reporter gene containing a 1.3-kb calcitonin promoter fragment in a hormone-dependent manner. As expected, mifepristone-complexed progesterone receptor B isoform fails to activate the calcitonin promoter. Progesterone acting through its nuclear receptor therefore regulates the expression of the calcitonin gene at the level of transcription. Finally, using RIA we investigated whether calcitonin is secreted from its glandular site of synthesis at the time of implantation by analyzing uterine flushings obtained from pregnant rats. We report the detection of a significant amount of calcitonin in the luminal secretions collected on day 4 and a lower amount on day 5 of gestation, whereas similar samples collected from animals on either day 3 or 6 of gestation did not contain detectable amounts of this peptide hormone. A transient burst of calcitonin secretion into the uterine lumen therefore occurs immediately preceding implantation. Based on these results, we propose that calcitonin is a measurable marker that forecasts the receptive state of rat endometrium during blastocyst implantation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.