{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,4]],"date-time":"2026-05-04T18:47:41Z","timestamp":1777920461992,"version":"3.51.4"},"reference-count":0,"publisher":"S. Karger AG","license":[{"start":{"date-parts":[[2008,4,7]],"date-time":"2008-04-07T00:00:00Z","timestamp":1207526400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/karger.com\/pages\/terms-and-conditions"},{"start":{"date-parts":[[2008,4,7]],"date-time":"2008-04-07T00:00:00Z","timestamp":1207526400000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/karger.com\/pages\/terms-and-conditions"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Neuroendocrinology"],"abstract":"<jats:p>Although the circadian variation of melatonin content in the pineal gland appears during the 3rd week of extrauterine life, recent studies suggest that the fetus perceives the day length through maternal melatonin transfer. Accordingly, we determined serum melatonin concentrations in pregnant and lactating rats and in their offsprings during the day (D) and at night (N). As compared with nonpregnant adult female rats (D: 6.0 \u00b1 0.5 and N: 112.0 \u00b1 5.0 pg\/ml), significant increases of serum melatonin concentrations, both during the day and at night, were observed in 21-day pregnant (D: 21.0 \u00b1 2.6 and N: 222.0 \u00b1 7.2 pg\/ml) and in 10-day (D: 20.0 \u00b1 2.6 and N: 145.0 \u00b1 12.3 pg\/ml) and 20-day (D: 19.0 \u00b1 1.2 and N: 140.0 \u00b1 8.0 pg\/ml) lactating animals, while a profound decrease was found in 5-day (D: 13.0 \u00b1 1.0 and N: 50.0 \u00b1 5.6 pg\/ml) lactating rats. In addition, melatonin levels were significantly higher during the night than during the day in all the experimental groups. High levels and circadian variation of serum melatonin were detected also in 21-day-old fetuses (D: 13.0 \u00b1 0.8 and N: 108.0 \u00b1 4.8 pg\/ml) and in 5- and 10-day-old suckling (in 5-day-old, D: 13.0 \u00b1 0.6 and N: 71.0 \u00b1 3.1 pg\/ml; in 10-day-old, D: 17.0 \u00b1 1.4 and N: 63.0 \u00b1 3.8 pg\/ml) rats. Circulating melatonin was not detectable in pinealectomized 21-day pregnant and 10-day lactating mothers, and in their offsprings, except for small amounts of melatonin determined at night in fetal (6.0 \u00b1 1.1 pg\/ml) and during the day (4.0 \u00b1 2.0 pg\/ml) and at night (15.0 \u00b1 2.5 pg\/ml) in suckling rats. These results demonstrate significant fluctuations of serum melatonin levels in pregnant and lactating rats and provide evidence that the circadian variations of circulating melatonin in fetal and suckling rats is dependent on maternal melatonin transfer.<\/jats:p>","DOI":"10.1159\/000126132","type":"journal-article","created":{"date-parts":[[2008,4,7]],"date-time":"2008-04-07T07:33:24Z","timestamp":1207553604000},"page":"321-326","source":"Crossref","is-referenced-by-count":22,"title":["Evidence That Circadian Variations of Circulating Melatonin Levels in Fetal and Suckling Rats Are Dependent on Maternal Melatonin Transfer"],"prefix":"10.1159","author":[{"given":"Esther","family":"Vel\u00e1zquez","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ana I.","family":"Esquifino","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jose Antonio","family":"Zueco","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Juan M.","family":"Ruiz Albusac","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Enrique","family":"Bl\u00e1zquez","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"127","published-online":{"date-parts":[[2008,4,7]]},"container-title":["Neuroendocrinology"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.karger.com\/Article\/Pdf\/126132","content-type":"application\/pdf","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/karger.com\/article-pdf\/doi\/10.1159\/000126132","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,5,1]],"date-time":"2026-05-01T19:31:16Z","timestamp":1777663876000},"score":1,"resource":{"primary":{"URL":"https:\/\/karger.com\/article\/doi\/10.1159\/000126132"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2008,4,7]]},"references-count":0,"URL":"https:\/\/doi.org\/10.1159\/000126132","archive":["Portico"],"relation":{},"ISSN":["0028-3835","1423-0194"],"issn-type":[{"value":"0028-3835","type":"print"},{"value":"1423-0194","type":"electronic"}],"subject":[],"published":{"date-parts":[[2008,4,7]]}}}