Comparative endocrinology on the pituitary gland of lampreys and hagfish

七鳃鳗和八目鳗是最古老的脊椎动物无颌类（无颌鱼）中仅存的两种代表。本研究旨在通过免疫组织化学和分子生物学技术阐明七鳃鳗和盲鳗的垂体系统。1)研究了七鳃鳗脑垂体腺垂体细胞的类型。结果发现，ACTH样细胞分布于远侧吻部的大部分区域，而中间部的几乎所有区域都有FSH样细胞。在远侧部近端，GH样细胞位于背侧，GTH样细胞位于腹侧。因此，至少有四种类型的腺垂体细胞存在于海七鳃鳗垂体。2)从七鳃鳗脑垂体中克隆了一个编码颌口动物生长激素保守氨基酸序列的cDNA，并从七鳃鳗脑垂体中分离了成熟蛋白。该蛋白质已被确定为七鳃鳗生长激素，通过证明在肝脏中的七鳃鳗IGF基因的表达增加。3)在海七鳃鳗在几个不同阶段的生命周期的腺垂体细胞类型的个体发育进行了研究。所获得的结果进行了讨论与海七鳃鳗的生命周期。4)本文研究了大西洋和太平洋盲鳗（Myxine spectrosa）、布氏粘盲鳗（Eptatretus burgeri）和副盲鳗（Paramyxine热海）垂体中免疫反应性腺垂体细胞的类型。在所有三个物种，三种不同类型的激素细胞检测腺垂体。它们是ACTH样细胞、GH样细胞和GTH样细胞。这表明ACTH、GH和GTH是古老的激素，在整个脊椎动物进化过程中保持其原始功能，而后来衍生的激素，如PRL和TSH，可能有助于脊椎动物向新环境的扩展。

Lampreys and hagfish are the only two extant representatives of the oldest class of vertebrates, Agnatha (jawless fishes). The present study aimed to elucidate the pituitary system of lampreys and hagfish by means of both immunohistochemical and molecular biological techniques. 1) Adenohypophysial cell types were studied in the sea lamprey (Petromyzon marinus) pituitary gland. It was found that ACTH-like cells were distributed in most parts of the rostral pars distalis, whereas MSH-like cells in almost all parts of the pars intermedia. In the proximal pars distalis, GH-like cells occupied the dorsal half, while GTH-like cells in the ventral half. Thus, at least four types of adenohypophysial cells are present in the sea lamprey pituitary. 2) A cDNA coding conserved amino acid sequence in gnathostome GHs has been cloned from the sea lamprey pituitary, followed by the isolation of the mature protein from the sea lamprey pituitary. That protein has been identified to be lamprey GH by demonstrating an increase of expression of lamprey IGF gene in the liver. 3) Ontogeny of adenohypophysial cell types was studied in sea lampreys at several different stages of the life cycle. Results obtained were discussed in connection with the life cycle of sea lampreys. 4) Immunoreactive adenohypophysial cell types were studied in the pituitary of the Atlantic and the Pacific hagfish, Myxine glutinosa, Eptatretus burgeri and Paramyxine atami. In all three species, three different types of hormone cells were detected in the adenohypophysis. They were ACTH-like cells, GH-like cells and GTH-like cells. It is suggested that ACTH, GH and GTH are ancient hormones and maintain their original functions throughout vertebrate evolution, while the later derived hormones, such as PRL and TSH, may have contributed to the expansion of vertebrates into new environments.