Yusuke Sagara

Maternal-fetal transfer of melatonin in pregnant women near term

Abstract: Our objective was to evaluate the maternal‐fetal transfer of melatonin in pregnant women. Serum melatonin concentration was measured by high‐performance liquid chromatography with electrochemical detection in a maternal vein and in the umbilical artery and umbilical vein at the time of birth. Blood samples were obtained from 12 women who had spontaneously delivered vaginally at night. A single oral dose of melatonin was administered to each of 33 patients who underwent a cesarean section, and. blood samples were taken at 1,2, 3, or 4 hr after the administration of melatonin at delivery. Cesarean section was performed between 1300 and 1500 hr. The mean melatonin concentrations of melatonin in maternal peripheral venous blood and umbilical arterial and umbilical venous blood did not differ significantly, and positive correlations in the serum levels of melatonin were observed between the three sources of blood. The oral administration of 3 mg of melatonin to pregnant women led to marked increases in the serum levels of melatonin, with maximum levels observed 2 hr (21.84 ± 2.09 ng/ml) after drug administration. Changes in serum levels of melatonin in the umbilical vein and artery resembled those found in the maternal vein. Serum melatonin concentrations did not differ significantly between the maternal vein and the umbilical veins. Serum levels of melatonin in the umbilical vein after the administration of melatonin were significantly and closely correlated with those in the maternal vein (r = 0.924, (P < 0.001). These results suggest that, in humans, melatonin is transferred from the maternal to the fetal circulation both easily and rapidly. A potential for the therapeutic use of melatonin as an antioxidant exists in the patients with preeclampsia.

Lipoprotein metabolism in postmenopausal and oophorectomized women

Objective To investigate the mechanisms of accumulating the cholesterol, and to analyze the metabolism of excess tissue cholesterol in women with low plasma levels of sex steroid hormones. Methods We measured plasma concentrations of cholesterol, triglyceride, apolipoproteins, sex steroid hormones, and lecithin cholesterol acyltransferase activity in 20 premenopausal, ten postmenopausal, and ten bilaterally oophorectomized women. Lipoprotein lipase and hepatic triglyceride lipase activities were measured in postheparin plasma. We compared the three groups and evaluated a correlation between lipid metabolism and sex steroid hormone concentrations. Results The mean plasma low-density lipoprotein (LDL) cholesterol level, lecithin cholesterol acyltransferase activity, and postheparin plasma lipoprotein lipase activity were higher in the postmenopausal and surgically menopausal groups. The mean plasma high-density lipoprotein (HDL) cholesterol concentration and postheparin plasma hepatic triglyceride lipase activity did not differ significantly among the three groups. The plasma LDL cholesterol level and postheparin plasma lipoprotein lipase activity showed a significantly negative correlation with plasma concentration of estrone (LDL: r = 0.64, P < .001; lipoprotein lipase: r = 0.54, P < .005) and estradiol (LDL: r = 0.65, P < .001; lipoprotein lipase: r = 0.47, P < .01), but not with that of testosterone. There was no significant relationship between postheparin plasma hepatic triglyceride lipase activity and plasma sex steroid hormones. Plasma lecithin cholesterol acyltransferase activity correlated significantly with plasma LDL cholesterol concentration, but not with levels of sex steroid hormones. Conclusion Because of low endogenous estrogens, enhanced postheparin plasma lipoprotein lipase activity may lead to an elevated plasma LDL cholesterol concentration in postmenopausal and bilaterally oophorectomized women. We demonstrated an accelerated cholesterol esterification in HDL cholesterol that may have been induced by LDL cholesterol accumulation, although the HDL cholesterol concentration remained unchanged.

Effects of estrogen on susceptibility to oxidation of low-density and high-density lipoprotein in postmenopausal women

OBJECTIVE To investigate the effects of estrogen on the susceptibility to oxidation of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) in postmenopausal women. METHODS A total of 23 postmenopausal women were treated with 0.625 mg of conjugated equine estrogen daily for 3 months. Blood samples were obtained before and after therapy. Plasma levels of total cholesterol and triglyceride and the concentrations of cholesterol, triglyceride, phospholipid in LDL and HDL were determined enzymatically and the levels of apolipoprotein A-I, A-II in HDL and apolipoprotein B in LDL were measured by turbidimetric immunoassay. The isolated LDL and HDL were incubated at 37 degrees C for 24 h with CuSO4 5 mumol/l and the lipid peroxide concentration of LDL and HDL was measured. RESULTS Estrogen significantly reduced the plasma level of total cholesterol and significantly increased the plasma level of triglyceride. The LDL concentrations of cholesterol, phospholipid and apolipoprotein B were significantly decreased following estrogen therapy. The triglyceride level of LDL did not change significantly. The HDL concentrations of cholesterol, triglyceride, phospholipid and apolipoprotein A-I and A-II were all significantly elevated after estrogen therapy. Estrogen significantly inhibited the peroxidation of LDL at 50-2000 micrograms of LDL protein (14.17 +/- 4.17-11.49 +/- 1.42 nmol/200 micrograms of LDL protein, P < 0.001) and of HDL (4.49 +/- 1.74-3.37 +/- 1.24 nmol/200 micrograms of HDL protein, P < 0.03) induced by their incubation in the presence of CuSO4. CONCLUSIONS Estrogen inhibited the susceptibility of LDL and HDL to oxidative modification and favorably affected lipid metabolism by reducing the number of LDL particles and increasing the number of HDL particles in plasma that were resistant to oxidation.

Effect of estrogen on the size of low-density lipoprotein particles in postmenopausal women

Objective To investigate the effects of estrogen on the size of low-density lipoprotein (LDL) particles in postmenopausal women. Methods We treated 20 postmenopausal women with 0.625 mg of conjugated equine estrogen daily for 3 months and measured the plasma levels of total cholesterol, triglyceride, high-density lipoprotein (HDL), and apolipoproteins A-I, A-II, and B before and after therapy. We also analyzed concentrations of LDL cholesterol and LDL apolipoprotein B. The diameter of LDL particles was determined by gradient gel electrophoresis. Results Estrogen caused significant decreases in the plasma levels of total cholesterol and apolipoprotein B and significant increases in the plasma levels of triglyceride, HDL cholesterol, and apolipoprotein A-I and A-II. Mean levels of LDL cholesterol and LDL apolipoprotein B were reduced significantly (by 16.31%, P < .001, and 16.91%, P < .001, respectively) after estrogen treatment. Estrogen also significantly reduced the size of LDL particles, from 25.74 ± 0.66 (mean ± standard deviation) to 24.95 ± 0.78 nm (P < .001). The LDL particle diameter correlated negatively with the plasma level of triglyceride (pre-treatment: r = 0.87, P < .001; post-treatment: r = 0.88, P < .001). Estrogen significantly increased the prevalence of LDL subclass pattern B, from 30 to 65% (P < .03). Conclusion Estrogen affects lipid metabolism favorably by reducing the plasma concentration of LDL particles. Estrogen-induced increase in the plasma level of triglyceride appears to reduce the size of LDL particles.

Estrogen-Induced Small Low-Density Lipoprotein Particles in Postmenopausal Women

Objective To investigate the mechanisms of an estrogen-induced decrease in the size of low-density lipoprotein (LDL) particles in postmenopausal women. Methods Twenty postmenopausal women were treated with conjugated equine estrogen, 0.625 mg daily, for 3 months. Plasma levels of total cholesterol, triglyceride, high-density lipoprotein (HDL) cholesterol, and apolipoproteins AI, AII, and B were measured before and after therapy. We analyzed total, free, and esterified cholesterol, triglyceride, phospholipid, and apolipoprotein B levels in the LDL. Cholesterol, triglyceride, and phospholipid concentrations were measured by enzymatic methods. Apolipoprotein AI, AII, and B levels were determined by immunoturbidimetric assay. The diameter of LDL particles was determined by gradient gel electrophoresis. Results Estrogen reduced significantly the plasma levels of total cholesterol and apolipoprotein B and increased significantly the plasma levels of triglyceride, HDL cholesterol, and apolipoproteins AI and AII. The ratio of cholesteryl ester to apolipoprotein B was significantly reduced, whereas the ratio of triglyceride to apolipoprotein B was significantly increased after such treatment. The plasma level of triglyceride showed a positive correlation with the ratio of LDL-triglyceride/apolipoprotein B (r = .40, P < .01), and a negative correlation with the ratio of LDL-cholesteryl ester/apolipoprotein B (r = −.55, P < .001). Estrogen treatment reduced significantly the diameter of LDL particles (25.79 ± 1.13 nm versus 24.94 ± 1.02 nm, P < .001). The diameter of the LDL particle was correlated negatively with the plasma level of triglyceride (r = −.84, P < .001) and the ratio of LDL-triglyceride/apolipoprotein B (r = −.58, P < .001), and positively with the ratio of LDL-cholesteryl ester/apolipoprotein B (r = .57, P < .001). Conclusion The results of this study indicate that an increase in the triglyceride plasma level induced by estrogen therapy appeared to produce small triglyceride-rich and cholesteryl ester-poor LDL particles that were of small size.

Role of melatonin in nocturnal prolactin secretion in women with normoprolactinemia and mild hyperprolactinemia

OBJECTIVE Our objective was to clarify the relationship between the nocturnal melatonin surge and the nocturnal prolactin release in women with normoprolactinemia and mild hyperprolactinemia. STUDY DESIGN Nocturnal serum melatonin and prolactin levels were determined for a various awake/sleep and light/dark conditions in a total of 23 healthy normoprolactinemia and 9 mild hyperprolactinemia. Patterns of prolactin and melatonin levels were subject to analysis of variance. RESULTS During sleep deprivation under continuous illumination in normoprolactinemia, neither melatonin nor prolactin increased in concentration. In contrast, during sleep deprivation in a dark environment, both hormones were increased. The maximal prolactin levels in mild hyperprolactinemia under physiologic sleep/dark were significantly higher (p < 0.01) and were reached 2 hours earlier than in normoprolactinemia. However, each woman with mild hyperprolactinemia had similar melatonin surges. Oral administration (1 mg) of melatonin to normoprolactinemia and mild hyperprolactinemia in the daytime resulted in release of prolactin in a fashion similar to that observed during the night. CONCLUSION Melatonin can regulate nocturnal prolactin secretion independent of sleep-related factors. Furthermore, the nature of the response to exogenous melatonin administration suggests that mild hyperprolactinemia may be unusually sensitive to melatonin.

Nocturnal changes in pineal melatonin synthesis during puberty : Relation to estrogen and progesterone levels in female rats

Okatani Y, Watanabe K, Morioka N, Hayashi K, Sagara Y. Nocturnal changes in pineal melatonin synthesis during puberty: Relation to estrogen and progesterone levels in female rats. J. Pineal Res. 1997; 22:33—41.

Enhanced nocturnal melatonin secretion in women with functional secondary amenorrhea: relationship to opioid system and endogenous estrogen levels.

The purpose of this study was to evaluate the role of the opioid system and the estrogen environment in the nocturnal secretion of melatonin in women with secondary amenorrhea (SA). Nocturnal melatonin concentrations in patients with SA were significantly higher than in normal women (p < 0.01 vs. women with normal menstrual cycles). There were significant negative correlations between cumulative melatonin levels (between 8 p.m. and 8 a.m.) and serum estradiol-17 beta (r = -0.561, p < 0.01) and between peak serum melatonin values and serum estradiol-17 beta concentrations (r = -0.608, p < 0.01) in SA. Intravenous administration of a conjugated estrogen (Premarin 20 mg) significantly suppressed nocturnal melatonin secretion (p < 0.05), but a continuous intravenous infusion of naloxone (1.6 mg/h from 8 p.m. to 6 a.m.), an opiate antagonist, did not affect nocturnal melatonin secretion in SA. Our findings suggest that elevated nocturnal melatonin secretion may be related to low estrogen levels, but that it is not mediated by the opioid system.

Effects of continuous medroxyprogesterone acetate on lipoprotein metabolism in postmenopausal women receiving estrogen

OBJECTIVE To investigate the effects of medroxyprogesterone acetate (MPA) on the beneficial effects of estrogen therapy on lipid metabolism in postmenopausal women. METHODS Postmenopausal women were administered either conjugated equine estrogen (CEE) 0.625 mg daily for 3 months (Group 1) or CEE 0.625 mg in conjunction with MPA 2.5 mg (Group 2) or MPA 5.0 mg (Group 3) daily for 3 months. Plasma levels of cholesterol, triglyceride, lipoprotein lipids, apolipoproteins, sex steroid hormones and lecithin cholesterol acyltransferase activity (LCAT) were determined. Lipoprotein lipase (LPL) and hepatic triglyceride lipase (H-TGL) activities were measured in postheparin plasma. Changes in the lipid concentrations and enzymatic activities were evaluated in each group. RESULTS Total, low-density lipoprotein (LDL) cholesterol, apolipoprotein B concentrations and LCAT activity were all significantly reduced by treatment in the three groups. The levels of high-density lipoprotein (HDL), HDL2, and HDL3 cholesterol as well as the levels of apolipoprotein AI and AII were significantly elevated in groups 1 and 2. The mean decrease in these parameters was related to the dose of MPA. Levels of triglyceride in the HDL and HDL2 were significantly increased in group 1. The levels of triglyceride in plasma, very low density lipoprotein (VLDL), LDL, HDL3 and VLDL cholesterol and LPL activity were unaffected. H-TGL activity was significantly inhibited only in groups 1 and 2. MPA produced a dose-dependent increase in H-TGL activity. A significant negative correlation was observed between the HDL cholesterol concentration and H-TGL activity (r = 0.58 P < 0.001). CONCLUSIONS The administration of MPA 2.5 mg and 5.0 mg did not adversely affect the changes in VLDL-LDL metabolism produced by estrogen. However, MPA has dose-dependent negative effects on HDL metabolism by increasing H-TGL activity and the 5.0 mg MPA interferes with the favorable effects on lipids of estrogen in postmenopausal women.

Oxidative damage in fetal rat brain induced by ischemia and subsequent reperfusion. Relation to arachidonic acid peroxidation.

To determine whether ischemia followed by subsequent reperfusion can induce fetal cerebral oxidative damage, we created a model of fetal ischemia/reperfusion using rats at day 19 of pregnancy. Fetal ischemia was induced by unilateral occlusion of the utero-ovarian artery for 20 min. Reperfusion was achieved by releasing the occlusion and restoring the circulation for 30 min. The opposite uterine horn was used as control. We measured brain mitochondrial respiratory control index (RCI) and the concentration of thiobarbituric acid-reactive substances (TBARS) in each group. Arachidonic acid (AA) peroxidation induced by the incubation of brain microvessel fraction and AA was measured. AA peroxidation was also evaluated with and without aspirin, an inhibitor of cyclooxygenase and phenidone, which inhibits both of cyclooxygenase and lipoxygenase. The RCI significantly decreased by the occlusion with (p < 0.01) or without reperfusion (p < 0.05). The TBARS level significantly increased with occlusion plus reperfusion (p < 0.01). AA peroxidation was significantly greater in the occlusion and occlusion plus reperfusion groups than in the control groups (p < 0.01). Aspirin did not affect peroxidation, while phenidone significantly inhibited it in a concentration-dependent manner (p < 0.001). Accordingly, ischemia followed by reperfusion is likely to induce fetal cerebral lipid peroxidation, which may inhibit mitochondrial respiratory activity. The phenidone-inhibited enzyme lipoxygenase may participate importantly in this peroxidation.