Vascular endothelial growth factor (VEGF) is known to be necessary for the vascularization of the developing corpus luteum. Our recent data suggested that cyclooxygenase-II (COX-II) may play a role in the formation of vascular plexuses in developing corpora lutea of the rat. Here we examined the relationship between VEGF and the expression of prostaglandin (PG)- metabolizing enzymes in rat ovarian luteal cells. VEGF treatment caused a dose-dependent increase in the expression of COX-II and membrane-associated PGE synthase (mPGES) mRNA in cultured rat luteal cells. However, pretreatment of the luteal cells with a selective COX-II inhibitor, NS-398, abolished the VEGF-enhanced mPGES mRNA expression. VEGF also increased PGE₂ secretion. Conversely, PGE₂ dose-dependently stimulated VEGF mRNA expression. Furthermore, VEGF induced VEGF mRNA expression, but this effect was abolished by NS-398 pretreatment. These findings suggest that VEGF enhances PGE₂ production by stimulating COX-II and mPGES expression in rat corpus luteum and that the effect of VEGF on luteal cells may be partially mediated by this stimulation of PGE₂ production.

Interleukin-6 (IL-6) and its receptor components have been shown to be present in rat follicular granulosa cells. The present study was designed to examine the effect of this cytokine on changes in expression of the luteinizing hormone receptor (LHR) messenger RNA and of the steroidogenic enzyme, CYP11A1 (cytochrome P450 scc) in an in vitro model of granulosa cell maturation. Ovarian granulosa cells harvested from immature rats 2 days after treatment with equine chorionic gonadotropin were cultured for 48 h in media containing 10% fetal bovine serum. They were then transferred to a chemically defined serum-free medium and cultured for an additional 72 h. Within 24 h of transfer, the expressions of LHR and CYP11A1 mRNA increased significantly and remained increased for 72 h. The cells responded to exposure to FSH, but not LH, by an increase in production of cAMP before the additional 72 h of culture. The cAMP response to LH was attained within 24 h and persisted for 72 h, whereas the response to FSH decreased continuously with time. Inclusion of IL-6 in the culture medium caused a dose-dependent decrease in expression of LHR mRNA, in addition to a decrease in the cAMP response to LH. Immunoneutralization of endogenous granulosa cell IL-6 resulted in an increase in expression of LHR mRNA, but not CYP11A1 mRNA. The results are consistent with the view that IL-6 may have a physiological role in the maturation of ovarian follicles by modulating the attainment of the LHR in granulosa cells.

ABSTRACT

The present study investigated possible sites through which ACTH or corticosterone inhibit progesterone secretion in pregnant rats, and the role of placental factors in blocking the inhibitory effect. The number of conceptuses was adjusted to one (1C group) or more than ten (FC group) on day 7 of pregnancy by aspirating the desired number. Serum concentrations of progesterone, testosterone and oestradiol were significantly (P<0·01) lower on day 15 in the 1C group than in the FC group. Corpora lutea (CL) obtained on day 15 were incubated for 6 h with corticosterone or ACTH. Corticosterone (1 μmol/l) significantly (P<0·05) inhibited progesterone secretion in the IC group but not in the FC group. The inhibitory effect of corticosterone in the IC group was completely blocked by co-addition of 1 μmol testosterone/l or 1 μmol oestradiol/l but not by 1 μmol dihydrotestosterone/l. ACTH (1 μg/l–1 mg/l) had no direct effect on progesterone secretion in either the IC or the FC groups, although ACTH apparently decreases progesterone secretion in vivo. Placentae obtained from rats of the FC group on day 15 were incubated for 24 h with or without ACTH (1 mg/l). The supernatant after placental incubation without ACTH significantly (P<0·01) increased progesterone secretion by the CL in both the IC and FC groups, and also eliminated the inhibitory effect of corticosterone in the IC group. The supernatant after placental incubation with ACTH also increased progesterone secretion in the FC group as effectively as the supernatant from the control incubation, but it had no effect in the IC group. It is concluded that corticosterone directly inhibits progesterone secretion by the CL, whereas the inhibitory effect of ACTH is mediated through the placenta. The results indicate that these inhibitory effects of corticosterone or ACTH are eliminated if the CL has been exposed to enough placental hormones before day 15 of pregnancy.

Journal of Endocrinology (1991) 129, 405–410

ABSTRACT

The effects of a conceptus-derived substance on the activity of 3β-hydroxysteroid dehydrogenase (3β-HSD) and 20α-HSD in the ovary were studied in the rat. On day 7 of pregnancy (day 1 = insemination), rats were laparotomized and the desired number of conceptuses was aspirated from the uterus; thus, rats carrying one, two, three, four, five to seven or eight to ten conceptuses were prepared. They were autopsied on day 15 and 3β-HSD and 20α-HSD activity in the corpus luteum (CL) or non-luteal ovarian tissue (NLO) was determined. Conceptus number was directly related to 3β-HSD and inversely related to 20α-HSD activity in the CL. The serum progesterone level and CL weight were also directly related to conceptus number. Neither 3β-HSD nor 20α-HSD activity in the NLO was affected by conceptus number. These results indicated that 3β-HSD and 20α-HSD in the CL are probably regulated by placental hormone secreted in proportion to the number of conceptuses; in the NLO these enzymes may be controlled by a different mechanism.

J. Endocr. (1984) 101, 285–288

Abstract

It has been surmised that GH exerts feedback action on the hypothalamus and thereby regulates its own secretion. Our previous studies suggested that GH acts on somatostatin neurons in the hypothalamic periventricular nucleus (PeV) and neuropeptide Y (NPY) neurons in the hypothalamic arcuate nucleus (ARC). However, there remains uncertainty whether GH acts directly or indirectly through the generation of IGFs on the hypothalamus to regulate its own secretion. To examine this, rat GH (rGH) or human IGF-I was injected directly into a defined area of the hypothalamus, and the blood GH profile was observed in conscious male rats. In the rats given 0·5 μg rGH into the ARC or PeV bilaterally, GH secretion was inhibited, and the inhibition lasted for 12 h. During the period of inhibition, the duration and amplitude of GH pulses were significantly decreased and the episodic secretion of GH appeared irregularly compared with the vehicle-injected control rats. In control rats given the vehicle or those given rGH into the lateral hypothalamus, the blood GH profile did not change and pulsatile GH secretion was produced every 3 h. When 0·1 μg IGF-I was injected into the ARC or PeV bilaterally, the blood GH secretory pattern was not affected. Together with the results of our previous studies showing that c-fos gene expression was induced by systemic administration of GH and that GH receptor mRNA was contained in somatostatin neurons in the PeV and NPY neurons in the ARC, the data of the present study indicate that GH, but not IGF-I, acts on the cells in the ARC and the PeV or in their vicinity to inhibit its own secretion, presumably by activating the somatostatin and NPY neurons.

Journal of Endocrinology (1997) 153, 283–290

Abstract

The purpose of this study was to examine the possible mechanism through which RU486 induces luteolysis during the late-luteal phase in pseudopregnant (PSP) rats. PSP rats received a subcutaneous injection of RU486 in sesame oil (5 mg/kg body weight) or sesame oil alone once a day between day 9 and day 11 of pseudopregnancy. Serial blood samples were collected on days 5, 9, 10, 11 and 12 and assayed for progesterone content. To examine the possible action of RU486 through a uterine and/or a pituitary (prolactin-dependent) mechanism, PSP rats and chronic hysterectomized PSP rats which had been hysterectomized before PSP induction received a subcutaneous injection of RU486 in sesame oil (5 mg/kg body weight), sesame oil alone, prolactin in 50% polyvinylpyrrolidone (15 IU/day), or RU486 and prolactin once a day between day 9 and day 11 of pseudopregnancy. Serial blood samples were collected on days 5, 9, 10 and 11 and assayed for progesterone content. Blood samples were also collected at 0400 h on day 12 and used for prolactin and progesterone determinations. To examine the direct effect of RU486 on corpus luteum and/or pituitary, hysterectomized rats underwent hypophysectomy and pituitary autotransplantation on dioestrus 1 and received a subcutaneous injection of RU486 in sesame oil or sesame oil alone for 3 days between day 21 and day 23 after surgery. Serial blood samples were collected on days 10, 21, 22, 23 and 24 and assayed for progesterone and prolactin contents.

In ordinary PSP rats, serum progesterone levels were significantly (P<0·01) lower in the RU486-treated group than in the control group (9 ± 1 vs 53 ± 7 ng/ml; mean ± s.e.m.) on day 11. Serum prolactin levels at 0400 h on day 12 of pseudopregnancy were significantly (P<0·05) lower in the RU486-treated group than in the control group (16 ±4 vs 154 ±44 ng/ml; mean ± s.e.m.). The concomitant prolactin treatment reversed the luteolytic effects of RU486 on day 11 of pseudopregnancy. In hysterectomized PSP rats, RU486 also suppressed serum prolactin levels, and the concomitant prolactin treatment again reversed the luteolytic effects of RU486. In hysterectomized rats which were hypophysectomized and pituitary autotransplanted, RU486 treatment did not induce any significant changes in serum progesterone and prolactin levels.

These results indicated that RU486 induced luteolysis during the late-luteal phase in PSP rats by suppressing prolactin secretion via a hypothalamic mechanism.

Journal of Endocrinology (1996) 150, 93–98

ABSTRACT

Immunohistochemical localization of 17α-hydroxylase/C17-20 lyase (P-450_17α,lyase) and aromatase cytochrome P-450 (P-450_arom) in polycystic ovary (PCO) syndrome was studied using specific polyclonal antibodies which had been raised against the corresponding enzymes. In the majority of follicles that were atretic and smaller than 7 mm in diameter, theca interna cells showed high P-450_17α,lyase immunoreaction, while small numbers of granulosa cells showed little P-450_arom immunoreaction. In some atretic follicles that were larger than 11 mm in diameter, the hyperplastic theca interna cell layer showed high immunoreaction to P-450_17α,lyase, while the poorly proliferated granulosa cell layer showed a mixture of weak and negative immunoreaction to P-450_arom. No immunoreaction to P-450_17α,lyase or P-450_arom was recognized in PCO stroma. These findings suggest that the theca interna cells and the granulosa cells from PCOs show abnormal steroidogenic function, while the localization of P-450_17α,lyase and P-450_arom in PCOs was essentially identical to that in the normal ovary. Theca interna cells in PCO atretic follicles are the main site of excess androgen production.

Journal of Endocrinology (1993) 139, 503–509

ABSTRACT

Immunohistochemical localization of 17α-hydroxylase/C17–20 lyase (P-450_17α,lyase) and aromatase cytochrome P-450 (P-450_arom) in normal human ovaries during the menstrual cycle was studied using specific polyclonal antibodies which were raised against corresponding enzymes. In the follicular phase of matured follicles, P-450_17α,lyase was localized in theca interna cells and P-450_arom in granulosa cells. P-450_17α,lyase was expressed in theca interna cells before P-450_arom was expressed in granulosa cells. The corpus luteum showed immunoreactivity to both enzymes and, after menstruation, immunoreactivity decreased gradually until it could not be detected in the corpus albicans. In corpus luteum graviditatis the immunoreactivity continued to be expressed strongly. In some atretic follicles, P-450_17α,lyase and/or P-450_arom continued to be expressed. In the stromal layer, P-450_17α,lyase was detected in secondary interstitial cells, which originated from the theca interna of atretic follicles, and P-450_arom was detected in hilar cells. Immunoreactivity to both enzymes was also detected in oocytes of developing follicles. These results are consistent with the two cell theory in the human ovary. They also suggest that androgens and oestrogens are produced not only by follicles and corpora lutea but also by stroma and oocytes.

Journal of Endocrinology (1992) 135, 589–595

ABSTRACT

Monoclonal antibodies (McAb) and polyclonal antibodies (PcAb) against human insulin-like growth factor-I (somatomedin C; hIGF-I) were produced. Using these two antibodies, an enzyme-linked immunosorbent assay (ELISA) system for hIGF-I was established. The ELISA system was able to detect hIGF-I at a range of 1–25 μg/l, compared with the range of 1–50 μg/l detected by radioimmunoassay (RIA). Human IGF-II and human insulin could not be recognized in this system. The plasma concentrations of IGF-I found using the ELISA agreed well with those found using RIA after conventional Sep-Pak C₁₈ cartridge pretreatment. Epitopes of hIGF-I to McAb and PcAb were investigated by enzymatic digestion of hIGF-I followed by comparing the affinity of the antibodies to the peptides obtained proteolytically. The epitope to McAb was found to be a peptide containing Leu¹⁰-Val¹¹-Asp¹² (epitope 2). Five epitopes to PcAb containing the following key fragments were identified: a conformational structure formed by the disulphide bonds between Cys⁶ and Cys⁴⁸, and between Cys⁴⁷ and Cys⁵² (epitope 1), Leu¹⁰-Val¹¹-Asp¹² (epitope 2), Val¹⁷-Cys¹⁸-Gly¹⁹-Asp²⁰ (epitope 3), Arg²¹-Gly²²-Phe²³-Tyr²⁴ (epitope 4) and Lys⁶⁸-Ser⁶⁹-Ala⁷⁰ (epitope 5). Of these, the peptide containing epitope 5 showed the highest affinity to PcAb. The results indicated that our ELISA system combined recognition by epitope 2 of McAb and recognition by epitope 5 of PcAb to obtain its good specificity.

Journal of Endocrinology (1990) 125, 327–335