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  • Author: Minoru Irahara x
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Toyokazu Kanematsu, Minoru Irahara, Toshikazu Miyake, Keiji Shitsukawa and Toshihiro Aono


The effects of insulin-like growth factor-I on gonadotropin release were studied using primary culture of rat anterior pituitary cells incubated with IGF-I (20-5000 μg/l) and a hypothalamus-pituitary perifusion system, in which either the mediobasal hypothalamus-pituitary unit or the pituitary were perifused with IGF-I (20-2000 μg/l). In primary cultures of rat anterior pituitary cells, IGF-I (2000 μg/l) caused a significant increase in the release of both LH (46% increase) and FSH (27% increase). It also caused a significant decrease in the cellular content of LH (9%) and FSH (19%). Its effects in stimulating gonadotropin release were suppressed by administration of anti IGF-I receptor antibody (1 mg/l). In the perifusion system, IGF-I (2000 μg/l) did not affect the LH release from the hypothalamus-pituitary or pituitary alone. However, it caused a significant increase in the GnRH (10−9 mol/l) stimulated LH release from perifused pituitary. These data suggest that IGF-I enhances pituitary gonadotropin release via the IGF-I receptor, but its effect on the hypothalamus was not confirmed.

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Keiji Shitsukawa, Minoru Irahara, Toyokazu Kanematsu, Keijiro Azuma and Toshihiro Aono


The effects of 2-buten-4-olide, an endogenous feeding suppressant, on the estrous cycle and LH secretion were studied to determine the influence of this compound on reproductive function. Estrous cycling female Wistar rats were treated ip with 2-buten-4-olide (0, 30 or 100 mg·kg−1·day−1) for 2 weeks. Treatment with 100 mg·kg−1·day−1delayed the estrous cycle. 2-Buten-4-olide increased the pituitary content of LH (1651.3±164.4 vs 927.7±65.1 ng/pituitary; p<0.01), and decreased the serum LH level compared with the control level in diestrus (0.16±0.01 vs 0.26±0.03 μg/l; p<0.05). However, it did not affect the GnRH content of the mediobasal hypothalamus. The direct effects of 2-buten-4-olide on the pituitary response to GnRH was examined by perifusing the pituitary. Medium containing 2-buten-4-olide (10−4 mol/l) suppressed the pituitary response to GnRH (2 μg/l) (percent increase at 50 min after start of GnRH stimulation: 180±47 vs 406±66%; p<0.05). These findings suggest that 2-buten-4-olide is involved in the regulation of pituitary gonadotropin secretion directly by suppressing the pituitary responsiveness to GnRH, and that 2-buten-4-olide may play an important role in starvation-induced anestrus.

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Seiichiro Saito, Keiji Shitsukawa, Minoru Irahara, Toshiya Matsuzaki and Toshihiro Aono

The effects of 2-buten-4-olide (2-B40), an endogenous feeding suppressant, on the secretion of luteinizing hormone (LH) were studied in ovariectomized rats. Intraperitoneal (ip) administration of 2-B40: adult female ovariectomized Wistar rats were given daily ip injections of solution containing 2-B40 at 0, 50 or 100 mg/kg body wt for 14 days. This ip treatment with 2-B40 significantly decreased the mean LH concentration and pulse frequency of LH. Intravenous (iv) administration of 2-B40: a solution of 2-B40 (50 or 100 mg/kg body wt) was slowly injected through an intra-atrium catheter and blood samples were taken every 6 min for 2 h. This iv treatment significantly suppressed the LH pulse frequency but had no significant effect on the LH amplitude or mean LH. Injection of 2-B40 into the third cerebroventricle: the injection of 2-B40 into the third cerebroventricle of freely moving rats decreased the mean LH concentration and the frequency and amplitude of LH pulses. Third cerebroventricle injection of a corticotropin-releasing factor (CRF) receptor antagonist before third cerebroventricle injection of 2-B40: the specific CRF receptor antagonist α-helical-CRF (9–41) was injected into the third cerebroventricle of ovariectomized rats before injection of 2-B40. Administration of 2-B40 into the third cerebroventricle significantly decreased the mean LH, concentration and pulse frequency. Third cerebroventricle injection of the CRF antagonist at 50 μg/rat and then 2-B40 also resulted in significant suppression of the mean LH concentration and pulse frequency. These findings suggest that 2-B40 may suppress gonadotropin-releasing hormone secretion in ovariectomized rats and that its effect in decreasing LH pulses may not be caused through the CRF pathway.

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Takahide Mori, Minoru Irahara, Haruhiko Saito, Yoshio Ohno and Eiji Hosoi

Abstract. To investigate the physiological importance of somatotrophin release-inhibiting factor (SRIF), effects in vitro of synthetic SRIF 14 on germinal vesicle breakdown (GVB) of cultured porcine follicular ova were studied. The proportion of ova with GVB decreased gradually and significantly with increasing concentrations of SRIF 14 in the range from 6 × 10−12 to 6 × 10−7 m during a 22 h period of culture. The inhibitory effect was apparent for the period between 14 and 22 h in the course of culture but was reversed by a concomitant addition of anti-SRIF to the medium. Neither synthetic oxytocin, vasoactive intestinal polypeptide nor substance P exerted any inhibitory or stimulatory action on GVB. These results suggest a limited but definite inhibitory action of SRIF on GVB of porcine ova.

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Naoto Yoneda, Minoru Irahara, Seiichiro Saito, Hirokazu Uemura and Toshihiro Aono

Yoneda N, Irahara M, Saito S, Uemura H, Aono T. Usefulness of recombinant human prolactin for treatment of poor puerperal lactation in a rat model. Eur J Endocrinol 1995;133:613–7. ISSN 0804–4643

Recombinant human prolactin (r-hPRL) was produced by a line of murine C127 cells transfected with human PRL gene. To assess the biological efficacy of r-hPRL in vivo, we studied its influence on milk secretion using a rat model in which lactation was reduced by bromocriptine treatment. Puerperal rats were injected daily for 9 days after delivery with bromocriptine or bromocriptine plus r-hPRL, and lactational performance was assessed by weighing the pups. The concentrations of rat and human PRL in rat serum were measured by specific radioimmunoassays and the mammary glands were examined on postpartum day 10. Daily injection of bromocriptine (0.1 mg/rat) significantly reduced the endogenous level of rat PRL and impaired the weight gain of the pups. Administration of r-hPRL increased the serum level of human PRL. Daily injections of r-hPRL (50 μg/rat, twice a day) restored lactational performance and significantly increased the weight of the pups. The detrimental effect of bromocriptine on the mammary glands, assessed by both weight and histological appearance, was reversed by administration of r-hPRL. These results demonstrate that r-hPRL is biologically active in vivo and replacement therapy of r-hPRL is effective in improving the lactational performance in bromocriptine-treated rats, and also that r-hPRL may be useful for the treatment of women with poor lactation.

Naoto Yoneda, Department of Obstetrics and Gynecology, School of Medicine, The University of Tokushima, 3-18-15 Kuramoto, Tokushima 770, Japan

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Toshiyuki Yasui, Ayako Saijo, Hirokazu Uemura, Toshiya Matsuzaki, Naoko Tsuchiya, Mitsutoshi Yuzurihara, Yoshio Kase and Minoru Irahara


The aim of the present study was to determine the different effects of oral estrogen therapy (ET) and transdermal ET on changes in circulating levels of cytokines and chemokines in relationship to changes in markers of inflammation in postmenopausal women with hysterectomy.


Fifty-five postmenopausal women with hysterectomy were randomly assigned in open, parallel-group fashion to an oral ET group and a transdermal ET group. Serum levels of cytokines and chemokines were simultaneously measured using a multiplexed human cytokine assay. Serum concentrations of high-sensitive C-reactive protein, soluble vascular cell adhesion molecule-1, soluble intercellular adhesion molecule-1, and E-selectin were measured as vascular inflammation markers.


Both oral ET and transdermal ET significantly decreased serum interleukin (IL)-7 concentrations at 12 months (P=0.020 and P=0.015 respectively). Transdermal ET decreased serum concentrations of IL-8, monocyte chemoattractant protein (MCP)-1, and macrophage inflammatory protein (MIP)-1β (P=0.05, P=0.019, and P=0.029), but oral ET increased IL-8 level (P=0.025). There were significant differences in percentage changes in IL-8 and MIP-1β between the oral and transdermal ET groups. Oral ET significantly decreased E-selectin level after 12 months.


Transdermal ET reduces circulating levels of IL-8, MCP-1, and MIP-1β, while both oral ET and transdermal ET reduce circulating level of IL-7.

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Hiroshi Ikawa, Minoru Irahara, Toshiya Matsuzaki, Seiichiro Saito, Toshiaki Sano and Toshihiro Aono

Prolactin (PRL) secretion in streptozotocin-induced diabetic rats postpartum was examined to elucidate the reason for the reduced milk secretion of diabetic mothers. Pregnant Wistar rats were given citrate buffer (control group) or streptozotocin only (DM group) or with insulin (insulin group). Growth of pups was significantly lower in the DM group than in the control group, but similar in the insulin and control groups. Suckling-induced PRL secretion was significantly lower in the DM group than in the control group, and intermediate in the insulin group. TRH-induced PRL secretion was significantly lower in the DM group than in the control group, but the same in the insulin and control groups. Histologically, the mammary glands in the DM group were relatively less developed than those in the control group. The results suggest that reduced milk secretion in diabetic mothers is due to impaired induction by suckling of PRL secretion from the anterior pituitary as well as poor development of the mammary gland.

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Takahide Mori, Haruhiko Saito, Yoshio Ohno, Minoru Irahara, Eiji Hosoi and Shiro Saito

Abstract. Measurement of somatostatin (SRIF) by RIA in porcine ovarian tissues after removal of the follicular fluid revealed the existence of immunoreactive (IR) SRIF at concentrations of 2.2 ± 0.6 ng/g wet weight (mean ± sd). On gel chromatographic analysis of ovarian extracts one major and two minor components with SRIF-like immunoreactivities have been detected. The major component comprised 59.5 ± 15.1% of the total IR-SRIF and was coeluted with synthetic tetradecapeptide (SRIF 14). The two other components seemed to have almost the same molecular weights as synthetic octacosapeptide (SRIF 28) (25.1 ± 10%) and pro-somatostatin (15.4 ± 5.5%), respectively. It is concluded that SRIF in porcine ovaries is heterogeneous, comprising SRIF 14 as a major component, as well as larger forms of SRIF which probably represent SRIF precursors.