Structure of the nephron and sites of action of hormones with special reference to hydro-mineral metabolism in the kidney of the bullfrog.

本研究旨在阐明不同激素在牛蛙肾脏中肾单位的作用部位。这些激素是精氨酸催产素(AVT)、催产素(MST)和甲状旁腺激素(PTH)。在此基础上，用光镜和电子显微镜观察了牛蛙肾脏的形态结构，并对牛蛙肾脏连续切片进行了肾单位的重建。然后，我使用了一种显微技术，可以在含有通过显微解剖从胶原酶处理的肾脏组织中分离出的一段局部小管的样本中测量激素依赖型腺苷环化酶的活性。每个肾单位由以下部分组成：肾小体、纤毛颈段、近端小管、纤毛中间段、远端小管、连接小管和集合管。早期远端小管和连接小管的细胞超微结构与哺乳动物的厚链…相似。皮质部集合管和皮质集合管分别较多。方法在肾显微解剖切片上观察激素对细胞内cAMP产生的影响。激素的作用(1)AVT：肾小体、近端、远端和连接小管的基础cAMP水平无显著差异。但春季的基础水平高于晚秋。当AVT(1um)加入孵育液中时，AVT可激活远端肾小管和连接小管cAMP的生成，但对肾小体和近端肾小管cAMP的生成无明显影响。然而，在晚秋采集的蛙的早期远端小管中，没有观察到明显的对AVT的反应。这些结果表明，牛蛙肾脏的远端小管和连接小管上可能存在V2型受体。牛蛙肾单位对AVT的反应可能存在季节差异。(2)甲状旁腺素：两者对cAMP的形成均无刺激作用。近端小管和远端小管。在两段小管中观察到的cAMP形成缺乏激素刺激，可能反映了这些制剂中与cAMP生成系统相关的激素受体的完全缺乏，它们的存在数量非常少，或者是本研究中使用的方法无法检测到它们的事实。(3)MST和降钙素：由于目前正在对这些激素进行研究，因此没有足够的数据来得出结论。较少

The present study was projected to elucidate the sites of action for various hormones along the nephrons in the kidney of the bullfrog. Those hormones are arginine vasotocin (AVT), mesotocin (MST) and parathyroid hormone (PTH). On the basis of this study, morphological observation of the kidney was examined by light and electron microscopy and the reconstruction of the nephron was obtained from a serial section of the kidney of a bullfrog. Then, I used a microtechnique that allows hormone-dependent adenylate cyclase activity to be measured in samples containing a localized piece of tubules isolated by microdissection from collagenase-treated kidney tissue.1. MorphologyEach nephron consists of the following parts : renal corpuscle, ciliated neck segment, proximal tubule, ciliated intermediate segment, distal tubule, connecting tubule, and collecting duct. The cellular ultrastructures of the early distal and the connecting tubules have resemblance to those of the mammalian thick ascendin … More g limb and of the cortical collecting tubule, respectively.2. MethodologyCellular production of cAMP in response to hormone was examined in microdissected segments of the nephron.3. Effects of Hormones(1) AVT : The basal levels of cAMP were not significantly different among the segments (renal corpuscle, proximal, distal and connecting tubules). However, the basal levels were higher in spring than in late autumn. When AVT (1 muM) was added to the incubation medium, AVT activated the production of cAMP in both distal and connecting tubules but not in the renal corpuscle and proximal tubule. However, no appreciable responses to AVT were observed in the early distal tubules from frogs collected in late autumn. These results suggest that V_2-type receptors may be present in both distal and connecting tubules of the bullfrog kidney. Seasonal differences may exist with respect to the responsiveness to AVT of the nephrons of the bullfrog.(2) PTH : There was no stimulation of cAMP formation by PTH in both. the proximal and the distall tubules. The lack of hormonal stimulation of cAMP formation observed in both segments of tubules might reflect either the total absence of hormonal receptors associated either a cAMP-generating system in these preparations, their presence in only very small quantity, or the fact that they are not detectable by the methods used in this study.(3) MST and calcitonin : As study of these hormones is now being carried out, enough data to get conclusion are not available. Less