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K. Seki, K. Kato and T. Tabei

Summary. Serum relaxin concentrations were measured every 30 min during a 24-h period in nonpregnant and pregnant women. Relaxin was undetectable in all serum samples obtained from 3 nonpregnant women. Relaxin was detectable in all serum samples obtained from 2 pregnant women. However, neither episodic secretion of relaxin nor a 24-h rhythm in relaxin secretion was discernible in these women.

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H. Kato, K. Nanjo, F. Numa, Y. Nakamura, K. Ueda, H. Inoguchi and T. Torigoe

Summary. Conceptus number was reduced to one on Day 7 of pregnancy in rats by aspirating all but a single conceptus (Group E) or left at ≥ 8 conceptuses (Group C). In Group E rats, serum progesterone concentrations remained low from Day 12 until autopsy at Day 21. Hypophysectomy on Day 12 significantly increased serum progesterone values after Day 17 of pregnancy, and these increases were blocked by treatment with ACTH (10 U/day, i.p., Days 12–17). Adrenalectomy on Day 12 also induced slight, but statistically significant, increases in serum progesterone concentration after Day 17, and these were overcome by implantation of a 10 mg capsule of corticosterone. In Group C rats, hypophysectomy or adrenalectomy on Day 12 did not change serum progesterone concentrations, but 40 U ACTH/day inhibited progesterone secretion. We conclude from these results that the pituitary–adrenal system exerts inhibitory effects on progesterone secretion during mid-pregnancy in rats.

Keywords: ACTH; corticosterone; corpus luteum; rat; pregnancy

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K. Shimamura, N. Sugino, Y. Yoshida, Y. Nakamura, K. Ogino and H. Kato

This study investigated the involvement of lipid peroxidation and antioxidant enzymes in the regulation of luteal function in pseudopregnant rats. The activities of superoxide dismutase (SOD), a specific scavenger of superoxide radicals, and glutathione peroxidase, a scavenger of hydrogen peroxide, and lipid peroxide concentrations were measured in the corpus luteum on days 1, 3, 5, 7, 9, 11 and 13 of pseudopregnancy. The activity of SOD in the corpus luteum gradually increased until day 9 of pseudopregnancy and decreased thereafter, in a similar manner to serum progesterone concentration. Glutathione peroxidase activity significantly increased from day 1 to day 3 and remained high until day 11 of pseudopregnancy. The concentrations of lipid peroxides in the corpus luteum increased from day 3 to day 13 of pseudopregnancy. The involvement of prostaglandin F (PGF) in the production of lipid peroxides in regression of the corpus luteum was investigated by administering PGF (3 mg kg−1, s.c.) or saline on days 7, 9 and 12 of pseudopregnancy. Each group of rats was autopsied 2 h later, and SOD activity, glutathione peroxidase activity and the concentration of lipid peroxides in the corpus luteum were determined. PGF significantly increased lipid peroxide concentrations in the corpus luteum on days 7, 9 and 12 of pseudopregnancy (approximately twofold increases on days 7 and 9, and a fivefold increase on day 12, compared with the control that received saline). The activity of SOD in the corpus luteum was significantly increased by PGF on days 7 and 9, but not on day 12, of pseudopregnancy. PGF did not cause any significant changes in glutathione peroxidase activity in the corpus luteum on days 7, 9 and 12 of pseudopregnancy. It is concluded that lipid peroxides play an important role in regulating luteal function in pseudopregnant rats.

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N. Sugino, Y. Nakamura, N. Okuno, K. Shimamura, T. Teyama, M. Ishimatsu and H. Kato

This study was undertaken to investigate the relationship between the inhibitory effect of restraint stress and the protective effect of the feto–placental luteotrophic factors on luteal function during mid-pregnancy in rats. The number of conceptuses was adjusted to one (1C group) or more than ten (FC group) on day 7 of pregnancy, and each rat received restraint stress from day 12 to day 17 of pregnancy. Restraint stress consisted of placing a rat individually in a small plastic holder three times a day for 1 h each time. Restraint stress significantly decreased serum progesterone concentration on day 17 of pregnancy in the 1C group, but not in the FC group. Restraint stress also decreased serum progesterone concentration on day 17 of pregnancy in the IC group which received bilateral adrenalectomy on day 12 of pregnancy. The number of animals with fetal resorption in this group of rats (10 out of 14 animals) was significantly greater than in any other group of rats. The number of animals with fetal resorption in the adrenalectomized IC group was significantly lower after daily injections of 4 mg progesterone from day 12 to day 17 of pregnancy. In the FC group of rats, even in adrenalectomized rats, restraint stress did not cause any changes in serum progesterone concentration or fetal loss. These data indicate that restraint stress is luteolytic and causes fetal loss during mid-pregnancy; this effect can be blocked by some factors from conceptuses, as occurred in the FC group.