Gazourian L, Deragon K L, Chase C F, Pati D, Habibi H R, Sower S A
Department of Biochemistry and Molecular Biology, University of New Hampshire, Durham, New Hampshire, 03824, USA.
Gen Comp Endocrinol. 1997 Nov;108(2):327-39. doi: 10.1006/gcen.1997.6981.
In the present study, both lamprey GnRH-I and -III stimulated steroidogenesis and induced ovulation in adult female sea lampreys during their final reproductive stage. One injection of lamprey GnRH-III at 0.1 or 0.2 microg/g lamprey stimulated plasma estradiol levels in lampreys held at each of three water temperatures, 13 degrees , 17 degrees , and 19 degrees , corresponding to increasing stages of maturation. Four successive injections, 3 to 4 days apart, of lamprey GnRH-III at 0.1 or 0.2 microg/g body weight induced ovulation in 100 or 88% of lampreys, respectively, compared to 21% in controls by Day 31. Lamprey GnRH-III also had a direct stimulatory effect on estradiol production in the sea lamprey gonads in vitro. Lamprey GnRH-III at 100 or 1000 ng/ml stimulated estradiol levels in media incubated with either lamprey ovaries or testes. In contrast to a previous finding in which lamprey GnRH-III was more potent than lamprey GnRH-I in inducing spermiation in adult male sea lampreys (Deragon and Sower, 1994), the results from the present study indicate that lamprey GnRH-I and -III are equally potent in inducing ovulation and stimulating steroidogenesis in female sea lampreys. In addition, GnRH binding sites have been demonstrated for the first time in both the testis and the ovary of the adult sea lamprey using an analog of mammalian GnRH ([D-Lys6] mammalian GnRH) as a labeled ligand. Scatchard analysis suggested the presence of a high affinity binding site in both the testis and the ovary. In summary, lamprey GnRH-III is biologically active in stimulating the pituitary-gonadal axis in adult female sea lampreys. This is the first report demonstrating the presence of a GnRH binding site in the gonads of an Agnathan. The evidence for a direct stimulatory effect of lamprey GnRH in the gonads, the presence of GnRH binding site, and the absence of GnRH in the plasma suggest that, like other vertebrates including rat, rabbit, teleost fish, and human, there may be a GnRH-like factor produced in the gonads of the lamprey and it may act as a paracrine/autocrine modulator of gonadal function. This study further strengthens the paracrine regulatory role of GnRH peptides in the gonads of vertebrates, which appear to be evolutionarily conserved.
在本研究中，七鳃鳗促性腺激素释放激素-I（GnRH-I）和-III（GnRH-III）均能刺激处于最终生殖阶段的成年雌性海七鳃鳗的类固醇生成并诱导排卵。以0.1或0.2微克/克七鳃鳗的剂量单次注射七鳃鳗GnRH-III，可刺激处于13℃、17℃和19℃三种水温下的七鳃鳗的血浆雌二醇水平，这三种水温分别对应着七鳃鳗不同的成熟阶段。每隔3至4天连续四次注射0.1或0.2微克/克体重的七鳃鳗GnRH-III，分别使100%或88%的七鳃鳗排卵，相比之下，到第31天时对照组的排卵率为21%。七鳃鳗GnRH-III对体外培养的海七鳃鳗性腺中雌二醇的产生也有直接刺激作用。100或1000纳克/毫升的七鳃鳗GnRH-III可刺激与七鳃鳗卵巢或睾丸共同孵育的培养基中的雌二醇水平。与之前的一项研究结果相反，在之前的研究中七鳃鳗GnRH-III在诱导成年雄性海七鳃鳗排精方面比七鳃鳗GnRH-I更有效（德拉贡和索尔，1994年），本研究结果表明，七鳃鳗GnRH-I和-III在诱导雌性海七鳃鳗排卵和刺激类固醇生成方面具有同等效力。此外，首次使用哺乳动物GnRH的类似物（[D-赖氨酸6]哺乳动物GnRH）作为标记配体，在成年海七鳃鳗的睾丸和卵巢中均证实了GnRH结合位点。斯卡查德分析表明，睾丸和卵巢中均存在高亲和力结合位点。总之，七鳃鳗GnRH-III在刺激成年雌性海七鳃鳗的垂体-性腺轴方面具有生物学活性。这是首次报道在无颌类动物的性腺中存在GnRH结合位点。七鳃鳗GnRH对性腺有直接刺激作用、存在GnRH结合位点以及血浆中不存在GnRH的证据表明，与包括大鼠、兔子、硬骨鱼和人类在内的其他脊椎动物一样，七鳃鳗的性腺中可能产生一种GnRH样因子，它可能作为性腺功能的旁分泌/自分泌调节剂发挥作用。本研究进一步强化了GnRH肽在脊椎动物性腺中的旁分泌调节作用，这种作用在进化上似乎是保守的。
