Duggal P S, Weitsman S R, Magoffin D A, Norman R J
Reproductive Medicine Unit, Department of Obstetrics and Gynaecology, The University of Adelaide, The Queen Elizabeth Hospital, Woodville 5011, SA, Australia.
Reproduction. 2002 Jun;123(6):899-905. doi: 10.1530/rep.0.1230899.
Leptin is secreted by adipocytes and exerts its effects by interacting with the long form of the leptin receptor, OB-RB. The leptin protein and leptin receptors have been localized in the ovary, and acute leptin treatment directly inhibits ovulation in the rat ovary. It was hypothesized that expression of the leptin receptor gene varies throughout the oestrous cycle to modulate the sensitivity of the ovary to leptin. In this study, expression of genes for the long and short isoforms of the leptin receptor in the adult ovary was investigated at different stages of the rat oestrous cycle. Vaginal cytology was used to determine the stage of the oestrous cycle. Ovaries were collected and RNA was extracted for real-time RT-PCR analysis of leptin receptor gene expression. OB-RB gene expression was low in pro-oestrus (3.13 +/- 0.18 fg RNA per microg total DNA) and dioestrus II (2.52 +/- 0.19 fg RNA per microg total DNA) of the oestrous cycle, whereas expression was high in oestrus (5.9 +/- 0.27 fg RNA per microg total DNA) and dioestrus I (4.6 +/- 0.24 fg RNA per microg total DNA) (P < 0.001). Expression of the gene for the short form of the leptin receptor (OB-RA) was at a maximum in dioestrus I (65.5 +/- 0.8 fg RNA per ng total DNA), high in oestrus (39.0 +/- 0.8 fg RNA per ng total DNA) and low at pro-oestrus (5.0 +/- 0.2 fg RNA per ng total DNA) and dioestrus II (1.1 +/- 0.09 fg RNA per ng total DNA) (P < 0.001). Plasma oestradiol concentrations (pg ml-1) were highest at pro-oestrus (19.38 +/- 1.3), and similar at the remaining three stages studied (oestrus: 13.7 +/- 1.9; dioestrus I: 12.4 +/- 1.0; dioestrus II: 10.3 +/- 0.9) (P < 0.05). Plasma progesterone concentrations (ng ml-1) were higher in the luteal phases of the oestrous cycle (dioestrus I: 18.6 +/- 2.3; dioestrus II: 14.7 +/- 2.5) than during pro-oestrus (5.12 +/- 0.6) and oestrus (5.9 +/- 0.8) (P < 0.05). Plasma leptin concentrations were detectable only in pro-oestrus (0.35 +/- 0.05 ng ml(-1)) and were below the detection limit of the assay at other stages of the oestrous cycle. In summary, mRNA content for the long and short isoforms of the leptin receptor is lower in pro-oestrus and dioestrus II than in oestrus and dioestrus I of the rat oestrous cycle. The fluctuations in leptin receptor mRNA content may be a response to the concentrations of circulating steroid hormones and leptin. This research supports the initial hypothesis and shows that ovarian leptin receptor concentrations vary throughout the oestrous cycle in response to the changing environment of the ovary.
瘦素由脂肪细胞分泌，并通过与瘦素受体的长形式OB-RB相互作用发挥其作用。瘦素蛋白和瘦素受体已定位在卵巢中，急性瘦素处理可直接抑制大鼠卵巢排卵。据推测，瘦素受体基因的表达在整个发情周期中会发生变化，以调节卵巢对瘦素的敏感性。在本研究中，对成年大鼠卵巢在发情周期不同阶段的瘦素受体长、短异构体基因的表达进行了研究。采用阴道细胞学方法确定发情周期阶段。收集卵巢并提取RNA，用于瘦素受体基因表达的实时逆转录聚合酶链反应（RT-PCR）分析。发情前期（每微克总DNA中为3.13±0.18 fg RNA）和动情后期II（每微克总DNA中为2.52±0.19 fg RNA）时OB-RB基因表达较低，而在发情期（每微克总DNA中为5.9±0.27 fg RNA）和动情后期I（每微克总DNA中为4.6±0.24 fg RNA）时表达较高（P<0.001）。瘦素受体短形式（OB-RA）基因的表达在动情后期I时最高（每纳克总DNA中为65.5±0.8 fg RNA），发情期时较高（每纳克总DNA中为39.0±0.8 fg RNA），发情前期（每纳克总DNA中为5.0±0.2 fg RNA）和动情后期II时较低（每纳克总DNA中为1.1±0.09 fg RNA）（P<0.001）。血浆雌二醇浓度（pg/ml）在发情前期最高（19.38±1.3），在研究的其余三个阶段相似（发情期：13.7±1.9；动情后期I：12.4±1.0；动情后期II：10.3±0.9）（P<0.05）。血浆孕酮浓度（ng/ml）在发情周期的黄体期（动情后期I：18.6±2.3；动情后期II：14.7±2.5）高于发情前期（5.12±0.6）和发情期（5.9±0.8）（P<0.05）。血浆瘦素浓度仅在发情前期可检测到（0.35±0.05 ng/ml(-1)），在发情周期的其他阶段低于检测限。总之，大鼠发情周期中，发情前期和动情后期II的瘦素受体长、短异构体的mRNA含量低于发情期和动情后期I。瘦素受体mRNA含量的波动可能是对循环类固醇激素和瘦素浓度的一种反应。本研究支持最初的假设，并表明卵巢瘦素受体浓度在整个发情周期中随卵巢环境变化而变化。
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