Zieba D A, Szczesna M, Klocek-Gorka B, Molik E, Misztal T, Williams G L, Romanowicz K, Stepien E, Keisler D H, Murawski M
Department of Sheep and Goat Breeding, University of Agriculture, 30-059 Krakow, Poland.
J Endocrinol. 2008 Jul;198(1):147-55. doi: 10.1677/JOE-07-0602. Epub 2008 May 1.
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 microg/kg BW; and 3) L2, roleptin, 1.0 microg/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.
近期研究表明，季节性哺乳动物的瘦素敏感性存在光周期变化。在此，我们研究了季节（长日照（LD）与短日照（SD））和重组羊瘦素（roleptin）对绵羊内侧基底部下丘脑（MBH）中褪黑素和催乳素（PRL）分泌以及细胞因子信号抑制因子3（SOCS-3）mRNA表达的相互作用。24只接受第三脑室（IIIV）插管手术的波兰长羊毛母羊，采用重复折返设计，每个季节12只母羊。季节内和重复实验的母羊被随机分配到三种处理之一（每种处理4只母羊），并在日落开始后的0、1和2小时进行三次中枢注射。处理方式为：1）对照组，林格洛克缓冲液；2）L1组，roleptin，0.5微克/千克体重；3）L2组，roleptin，1.0微克/千克体重。从输液开始前立即每隔15分钟采集颈静脉血样，并持续6小时。在采血结束后，至少经过3天的洗脱期，然后将母羊重新随机分组并接受上述处理之一（每种处理4只母羊）。之后处死母羊并采集大脑用于MBH处理。与对照组相比，在两个季节中，瘦素处理均以剂量依赖方式增加（P<0.001）循环瘦素浓度。总体而言，LD期间褪黑素的平均血浆浓度高于SD（P<0.001）。然而，瘦素处理在SD期间以剂量依赖方式增加褪黑素浓度，而在LD期间降低。同样，PRL的血浆浓度在LD期间高于SD（P<0.001）。然而，与褪黑素的变化不同，LD期间循环PRL对瘦素的反应降低（P<0.001）。半定量PCR显示，在LD期间，瘦素以剂量依赖方式增加（P<0.001）MBH区域中SOCS-3的表达。数据表明，在SD和LD期间，褪黑素和PRL等光周期激素的分泌受到瘦素的反向调节。然而，与SD相比，LD期间MBH中SOCS-3表达的增加并不能完全解释这些效应。
