Endocrine Control of Mammary Secretory Function in Concurrently Lactating-Pregnant Animals

Research Project

Project/Area Number	62560264
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	畜産学(含草地学)
Research Institution	Faculty of Agriculture, Shizuoka University
Principal Investigator	MIZUNO Hideo Faculty of Agriculture, Shizuoka University Professor, 農学部, 教授 (30022164)
Co-Investigator(Kenkyū-buntansha)	SENSUI Naoto Coll. of Agric. & Vet. Med., Nihon University Assist. Prof., 農獣医学部, 講師 (10060120) MORI Makoto Faculty of Agriculture, Shizuoka University Assoc. Prof., 農学部, 助教授 (90143411)
Project Period (FY)	1987 – 1988
Project Status	Completed (Fiscal Year 1988)
Budget Amount *help	¥1,900,000 (Direct Cost: ¥1,900,000) Fiscal Year 1988: ¥600,000 (Direct Cost: ¥600,000) Fiscal Year 1987: ¥1,300,000 (Direct Cost: ¥1,300,000)
Keywords	Lactating-Pregnant Animal / Mammary Function / Luteal Function / Embryo Transfer / Blood Sampling by Atrial Cannulation / Plasma Corticosterone Level / コルチコステロン濃度 / 乳腺分泌機能 / 胎盤性ラクトゲン活性 / 泌乳妊娠マウス / 連続採血法 / コルチコステロン
Research Abstract	Embryo transfer was tested in order to develop an effective method to establish concurrently lactating-pregnant(LP) mice. Four-day-old embryos were transferred into uterine horns of lactating(L) and lactating-pseudopregnant(LPP) mice at various days of lactation and checked for their maintenance at 12 days later. The high pregnancy rate was observed when embryos were transferred at 4-6 days of lactation and no significant difference existed between L and LPP mice. However, when suckling stimulus was withdrawn after embryo transfer the pregnancy rate was higher in LPP than L mice, suggesting that the cervical stimulation may exert some favorable effects on implantation and/or maintenance of embryos probably through luteal function. The in vitro production of progesterone by dispersed luteal cells taken from ovaries of L, LPP, LP and pregnant(P) mice at various days were measured by RIA. Higher production of progesterone was observed at the early stage of lactation in L and LPP mice. Pro … More gesterone production in L mice was higher during the early stage and also at the late stage of lactation. Plasma progeserone concentration did not differ between L and LPP mice. In any case, concurrent pregnancy could be established by embryo transfer at the early stage of lactation in lactating mice irrespective of cervical stimulation. however, the synchronization of implantation should be solved. A method of blood sampling by atrial cannulation was successful in this study. Validity for stressless of volumes and/or intervals of blood sampling was examined by plasma corticosterone levels. This method will be very useful for biological studies in mice. In PL mice the mammary DNA was 30 % more than in L mice but secretory function (RNA/DNA, lactose content) was markedly depressed. Cortisol administration stimulated the secretory activity. Plasma lactogenic activity measured by a rat Nb_2 lymbhoma cell assay showed 100 times of magnitude in LP than in L mice, indicating that very much placental lactogen was circulating in LP mice. It was was considered that the mammary tissues in lp mice consist of existing cells and newly developing cells and have relatively low responsiveness to lactogenic hormone(s). Further study is required to elucidate these problems. A preliminary study was carried out to establish an in vitro culture technique of lactating mammary tissues. Less