Uterine decidualization in hypophysectomized-ovariectomized rats: effects of pituitary hormones

Decidualization of the endometrial stroma occurs in rats in response to implanting blastocysts or after the application of an appropriately timed artificial stimulus. It is well established that decidualization is regulated by estrogens and progesterone (P). The present study investigated the role of pituitary hormones in this response. Decidualization produced by the bilateral intrauterine injection of 100 microliter sesame oil was compared in ovariectomized (OVX) and hypophysectomized (HYPOX)-OVX rats. All animals were treated with a sequence of 17 beta-estradiol (E2) and P that in OVX rats supported decidualization. As assessed by uterine weights 5 days after uterine stimulation, decidualization was much greater in OVX than in HYPOX-OVX rats (geometric mean uterine weights of 1539 and 376 mg, respectively). To determine the ability of pituitary hormones to restore decidualization in HYPOX-OVX rats, animals were treated with ovine prolactin (oPRL, 2 x 100 micrograms daily), bovine growth hormone (bGH, 2 x 125 micrograms daily), and thyroxine (1 microgram/day, replacement for thyrotropin) in addition to E2 and P. Combined treatment with bGH + thyroxine resulted in decidualization which was not significantly different from that obtained in OVX rats; the effects of bGH and thyroxine were additive. oPRL had no significant effect. Administration of bGH + thyroxine during the prestimulation period resulted in decidualization which did not differ significantly from that obtained when the hormones were administered both pre- and poststimulation; administration during the poststimulation period only, when growth and differentiation of decidual cells occurs, resulted in much less decidualization. Because an increase in endometrial vascular permeability is a prerequiste for decidualization, [125I]-labeled bovine serum albumin was used to assess permeability 8 h after uterine stimulation. Uterine concentrations of radioactivity indicated that endometrial vascular permeability was increased to the same extent in bGH + thyroxine-treated HYPOX-OVX rats as in OVX animals; this increase was significantly reduced in vehicle-treated HYPOX-OVX rats. Because prostaglandins (PGs) are involved in decidualization, the possibility that the reduced responses in vehicle-treated HYPOX-OVX rats were a consequence of a decreased capacity of the uterus to produce PGs in response to the deciduogenic stimulus was investigated. As indicated by uterine PGE and PGF concentrations 15 min after uterine stimulation, uterine PGE and PGF production was increased by the stimulus in both vehicle-treated and bGH + thyroxine-treated HYPOX-OVX rats.(ABSTRACT TRUNCATED AT 400 WORDS)