Lamar C A, Bhat G K, Mahesh V B, Brann D W
Department of Physiology, School of Medicine, Medical College of Georgia, Augusta, Ga., USA.
Neuroendocrinology. 1999 Nov;70(5):360-7. doi: 10.1159/000054497.
Nitric oxide (NO) has been implicated in the control of the proestrus luteinizing hormone (LH) surge in the rat but to date no studies have attempted to measure neuronal nitric oxide synthase (nNOS) or NO production on proestrus in the hypothalamus in order to determine if endogenous NO is increased on proestrus afternoon to activate gonadotropin-releasing hormone (GnRH) neurons. To address this deficit in our knowledge, we measured nNOS mRNA and protein levels as well as NOS activity levels in rat preoptic area (POA) and medial basal hypothalamus (MBH) fragments at 12.00, 14.00, 16.00, and 18.00 h of proestrus. Serum LH levels were also assessed to determine whether NOS changes correlate to the LH surge. To determine the specificity of observed changes we also measured mRNA levels for the enzyme heme oxygenase-2, which is responsible for production of another putative gaseous transmitter, carbon monoxide. In all studies a metestrus 12.00 h control group was included since steroid and LH levels would be basal at this time as compared to proestrus. The results revealed that nNOS mRNA and protein levels, as well as NOS activity did not change significantly in the MBH on proestrus. In contrast, nNOS mRNA levels were significantly elevated in the POA at proestrus 12.00 and 14.00 h, as compared to metestrus 12.00 h. Likewise, at the protein and activity level, nNOS protein levels in the POA were significantly elevated on proestrus at 14.00 and 16.00 h, with NOS activity significantly increased at 16.00 h on proestrus. The elevation of nNOS protein and activity levels in the POA occurred at the time of initiation of the LH surge. The elevation of nNOS was specific as mRNA levels for the CO-synthetic enzyme heme oxygenase-2 did not change significantly on proestrus in the POA or MBH. As a whole, the current studies provide new evidence that nNOS is elevated in the POA on proestrus, and thus could play a role in the activation of GnRH neurons to produce the preovulatory LH surge.
一氧化氮（NO）被认为与大鼠发情前期促黄体生成素（LH）峰的调控有关，但迄今为止，尚无研究试图测量下丘脑在发情前期的神经元型一氧化氮合酶（nNOS）或NO生成量，以确定内源性NO在发情前期下午是否增加，从而激活促性腺激素释放激素（GnRH）神经元。为填补这一知识空白，我们在发情前期的12:00、14:00、16:00和18:00测量了大鼠视前区（POA）和下丘脑内侧基底部（MBH）片段中的nNOS mRNA和蛋白水平以及NOS活性水平。还评估了血清LH水平，以确定NOS变化是否与LH峰相关。为确定观察到的变化的特异性，我们还测量了血红素加氧酶-2的mRNA水平，该酶负责另一种假定的气体递质一氧化碳的生成。在所有研究中，均纳入了动情间期12:00的对照组，因为此时与发情前期相比，类固醇和LH水平处于基础状态。结果显示，发情前期MBH中的nNOS mRNA和蛋白水平以及NOS活性均无显著变化。相比之下，与动情间期12:00相比，发情前期12:00和14:00时POA中的nNOS mRNA水平显著升高。同样，在蛋白和活性水平上，发情前期14:00和16:00时POA中的nNOS蛋白水平显著升高，发情前期16:00时NOS活性显著增加。POA中nNOS蛋白和活性水平的升高发生在LH峰开始之时。nNOS的升高具有特异性，因为POA或MBH中CO合成酶血红素加氧酶-2的mRNA水平在发情前期没有显著变化。总体而言，当前研究提供了新的证据，表明发情前期POA中的nNOS升高，因此可能在激活GnRH神经元以产生排卵前LH峰中发挥作用。
