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This Article Full Text Full Text (PDF) All Versions of this Article: JOE-07-0602v1 198/1/147    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Zieba, D A Articles by Murawski, M PubMed PubMed Citation Articles by Zieba, D A Articles by Murawski, M

Department of Sheep and Goat Breeding, University of Agriculture, 30-059 Krakow, Poland¹ Department of Endocrinology, Institute of Animal Physiology and Nutrition, 05-110 Jablonna, Poland² Animal Reproduction Laboratory, Texas A&M University Agricultural Research Station, Beeville, 78102 Texas, USA³ Independent Laboratory of Molecular Biology and Research, John Paul II Hospital in Krakow, 31-202 Krakow, Poland⁴ Department of Animal Science, University of Missouri, Columbia, 65211 Missouri, USA

(Correspondence should be addressed to D A Zieba; Email: rzzieba{at}cyf-kr.edu.pl)

Recent studies have demonstrated photoperiodic changes in leptin sensitivity of seasonal mammals. Herein, we examined the interaction of season (long days (LD) versus short days (SD)) and recombinant ovine leptin (roleptin) on secretion of melatonin and prolactin (PRL) and on mRNA expression of suppressor of cytokine signaling-3 (SOCS-3) in the medial basal hypothalamus (MBH) in sheep. Twenty-four Polish Longwool ewes, surgically fitted with third ventricle (IIIV) cannulas, were utilized in a replicated switchback design involving 12 ewes per season. Within-season and replicate ewes were assigned randomly to one of three treatments (four ewes/treatment) and infused centrally three times at 0, 1 and 2 h beginning at sunset. Treatments were 1) control, Ringer–Locke buffer; 2) L1, roleptin, 0.5 µg/kg BW; and 3) L2, roleptin, 1.0 µg/kg BW. Jugular blood samples were collected at 15-min intervals beginning immediately before the start of infusions and continued for 6 h. At the end of blood sampling, a washout period of at least 3 days elapsed before ewes were re-randomized and treated with one of the treatments described above (four ewes/treatment). Ewes were then killed and brains were collected for MBH processing. Leptin treatments increased (P<0.001) circulating leptin concentrations compared with controls during both seasons in a dose-dependent manner. Overall, mean plasma concentrations of melatonin were greater (P<0.001) during LD than SD. However, leptin treatments increased melatonin concentrations during SD in a dose-dependent manner and decreased it during LD. Similarly, plasma concentrations of PRL were greater (P<0.001) during LD than SD. However, unlike changes in melatonin, circulating PRL decreased (P<0.001) in response to leptin during LD. Semi-quantitative PCR revealed that leptin increased (P<0.001) SOCS-3 expression in the MBH region during LD in a dose-dependent manner. Data provide evidence that secretion of photoperiodic hormones such as melatonin and PRL are inversely regulated by leptin during SD and LD. However, the increase in expression of SOCS-3 in the MBH during LD compared with SD fails to fully explain these effects.