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I Chakraborty, S K Das and S K Dey

Abstract

Vascular endothelial growth factor (VEGF) is a mitogen for endothelial cells and an inducer of angiogenesis. VEGF is also known as a vascular permeability factor because it can stimulate vascular permeability. In the rodent, increased uterine vascular permeability occurs at the sites of blastocysts with the onset of the attachment reaction. This is followed by stromal decidualization and angiogenesis. We examined the temporal and spatial expression of VEGF and its receptors, Flk-1 and Flt-1, in the mouse uterus during the peri-implantation period (days 1–8) using Northern and in situ hybridization to assess the involvement of VEGF in the process of implantation. Primarily, a major (≈4·2 kb) transcript for VEGF mRNA was detected in uterine poly(A) samples, except for the presence of two other minor (≈3·7 and 2·5 kb) transcripts in decidual samples. The steady-state levels of these transcripts did not vary much during the peri-implantation period, except for an increase in day-8 decidual samples. Results of in situ hybridization experiments demonstrated accumulation of VEGF mRNA in the luminal epithelium on days 1 and 2. In contrast, stromal cells exhibited a modest level of signals on day 3. On day 4, luminal epithelial cells and those in the subepithelial stromal bed accumulated VEGF mRNA. On days 5–7, a clear cell type-specific accumulation of this mRNA was noted. On day 5 after the initial attachment reaction, luminal epithelial and stromal cells immediately surrounding the blastocyst exhibited accumulation of VEGF mRNA. On days 6–8, the accumulation occurred in cells in the decidual bed at both the mesometrial and antimesometrial poles. The embryo, especially the trophoblast giant cells, also accumulated VEGF mRNA on day 8.

The expression of the VEGF receptors, Flk-1 and Flt-1, was also examined. A single transcript (≈6·5-7·0 kb) for Flk-1 mRNA and two transcripts (≈6·5 and 7·5 kb) for that of Flt-1 were detected in poly(A)+ uterine RNA samples. In situ hybridization studies showed accumulation of Flk-1 mRNA in a subset of cells in the stromal bed on day 4, but not in any uterine cell types on day 1. On days 5–8, cells in both the mesometrial and antimesometrial decidual beds exhibited accumulation of Flk-1 and Flt-1 mRNAs. Lectin binding (Dolichos biflorus agglutinin) was used to identify newly sprouting endothelial cells (angiogenesis), while an antibody to the von Willebrand factor (vWF) was employed to identify endothelial cells in general. The results suggest that vWF-positive stromal cells on day 4 and cells in the antimesometrial decidual bed on days 5–8 correlated with the expression of Flk-1 mRNA, as did the vWF- and lectin-positive cells in the mesometrial decidual bed. This implies that cells involved in angiogenesis at the mesometrial pole express the VEGF receptor mRNAs. In contrast, perhaps the endothelial cells of the existing blood vessels in the stromal bed on day 4 and those in the antimesometrial decidual bed on days 5–8 accumulated the receptor mRNAs, suggesting an involvement of VEGF in changes in vascular permeability. Flk-1 mRNA was also detected in embryonic tissues on day 8.

Collectively, the results suggest that VEGF participates in increased vascular permeability and/or angiogenesis occurring in the uterine vascular bed during implantation. Further, the data suggest that VEGF is involved in trophoblast differentiation and invasion, as well as in decidualization and placentation.

Journal of Endocrinology (1995) 147, 339–352

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C. Chakraborty, D. L. Davis and S. K. Dey

ABSTRACT

Pig conceptuses display a surge in oestrogen and catecholoestrogen synthetic activity during the periimplantation period. However, the pathways of catecholoestrogen metabolism in pig conceptuses and endometrium are unknown. O-Methylation is an important route of catecholoestrogen metabolism. Therefore, the O-methylations of 2- and 4-hydroxy-oestradiols (2- and 4-OH-oestradiol) by cytosol of pig conceptuses and endometrium during the periimplantation period were studied. Kinetic studies performed in tissues obtained on day 13 of pregnancy (day 0 = first acceptance of the male) indicated that the O-methylation of 2-OH-oestradiol displayed simple Michaelis–Menten kinetics in both tissues. In blastocysts, the apparent Michaelis constant (K m) and maximum velocity (V max) for the O-methylation of 2-OH-oestradiol were 1·4 μmol/l and 11·27 pmol/mg protein per min respectively, and when 4-OH-oestradiol was used as substrate, the values were 2·53 μmol/l and 9·86 pmol/mg protein per min respectively. The apparent K m and V max values for the O-methylation of 2-OH-oestradiol in endometrium were 0·77 μmol/l and 19·6 pmol/mg protein per min respectively, and for the O-methylation of 4-OH-oestradiol were 2·44 μmol/l and 10·38 pmol/mg protein per min respectively. Ontogenesis of catechol-O-methyltransferase (COMT) in conceptuses and endometrium was studied from day 10 to day 19 of pregnancy. Conceptus COMT activity was lowest on day 10 and increased gradually to day 19 of pregnancy. Because a surge of oestradiol-2/4-hydroxylase activity occurs on days 11–13, less COMT activity on these days than on the later days of pregnancy is consistent with a role for catecholoestrogens in conceptus-maternal signalling during pregnancy establishment. Endometrial COMT activity on day 10 was higher than that on later days of pregnancy. Therefore, a role for COMT in modulation of catecholoestrogen and oestrogen function during the peri-implantation period is possible.

Journal of Endocrinology (1990) 127, 77–84

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J. L. Voogt, P. L. Pakrasi, D. C. Johnson and S. K. Dey

ABSTRACT

The present studies examined whether the pituitary hormones, particularly prolactin, have any role in the regulation of rat placental lactogen (rPL) secretion. Total rPL was measured using a lymphoma cell bioassay. Hypophysectomy on day 13 of pregnancy increased total serum rPL levels above those of intact control rats and delayed for 3 days the decline in rPL usually seen by day 14. To test the effect of early hypophysectomy on rPL secretion, a delayed implantation model was used. Hypophysectomy was carried out on day 3, progesterone (2 mg) was given daily until day 8 and oestrone (1·0 μg) was given on day 8. This initiated implantation on day 9, which is 4 days later than normal. Rats hypophysectomized on day 3 had high serum levels of rPL (10–13 mg/l) 7 days after initiation of implantation compared with control values of 2–3 mg/l, and these levels remained raised for the duration of the experiment. Termination of maintenance injections of steroids did not affect the high levels of rPL for several days, even though there was fetal and placental resorption. When a pair of anterior pituitaries was transplanted under the kidney capsule on day 13 (day 9 of development) of rats hypophysectomized on day 3, serum rPL levels still increased for the next 3 days. However, unlike similarly treated rats not receiving transplants, rPL levels fell rapidly thereafter and were only 5% of those in control animals 1 week later. Only the intact rats and those hypophysectomized either on day 3 or 13 and given daily maintenance doses of steroids had normal pregnancies; the other two groups in which steroid injections were stopped on day 15 showed various degrees of resorption or abortion. It is suggested that the pituitary, possibly because of its prolactin secretion, is important in the regulation of rPL secretion.

J. Endocr. (1985) 107, 121–126