Riegel JA
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
J Exp Biol. 1998 Nov;201 (Pt 22):3097-104. doi: 10.1242/jeb.201.22.3097.
The capillary tuft of glomeruli of the hagfish mesonephros contains both 'low'-pressure and 'high'-pressure glomerular vessels (LPGVs and HPGVs). The existence of the HPGV raised the possibility that pressure filtration could occur in the hagfish kidney when the blood pressure was sufficiently high. Therefore, measurements of glomerular capillary pressure were made in HPGVs and LPGVs whilst single glomeruli were perfused with hagfish Ringer's solution that contained the colloid Ficoll 70. Calculations of the effective colloid osmotic pressure in perfused capillaries were made; these showed that hydrostatic pressures within the HPGV were inadequate to effect pressure filtration except at high rates of perfusion. However, high rates of perfusion provoked perfusion pressures that exceeded the highest values measured in the renal blood supply of lightly anaesthetised hagfish. It was concluded that some process other than pressure filtration must account for formation of the primary urine by hagfish glomeruli. The proportion of the perfusate that became urine, the single glomerulus filtration fraction (SGFF), bore a strong positive relationship to the vascular resistance of perfused glomeruli. Both the SGFF and the vascular resistance were inversely related to the rate of perfusion except when that rate was very high. From these two observations it was concluded that at least two flow pathways exist in hagfish glomeruli: one that has a high vascular resistance and that contributes to the elaboration of the urine, and one that has a low vascular resistance and does not contribute to urine formation. The possible anatomical location of the various flow pathways through hagfish glomeruli and how they may function are discussed.
盲鳗中肾肾小球的毛细血管丛包含“低压”和“高压”肾小球血管（LPGV和HPGV）。HPGV的存在增加了一种可能性，即当血压足够高时，盲鳗肾脏可能会发生压力过滤。因此，在向单个肾小球灌注含有胶体Ficoll 70的盲鳗林格氏液时，对HPGV和LPGV中的肾小球毛细血管压力进行了测量。计算了灌注毛细血管中的有效胶体渗透压；结果表明，除了在高灌注速率下，HPGV内的静水压力不足以实现压力过滤。然而，高灌注速率引发的灌注压力超过了轻度麻醉盲鳗肾脏血液供应中测得的最高值。得出的结论是，盲鳗肾小球形成原尿的过程肯定不是压力过滤，而是其他过程。灌注液变成尿液的比例，即单个肾小球滤过分数（SGFF），与灌注肾小球的血管阻力呈强烈正相关。SGFF和血管阻力均与灌注速率呈负相关，除非灌注速率非常高。从这两个观察结果得出结论，盲鳗肾小球中至少存在两条血流途径：一条具有高血管阻力，有助于尿液的形成；另一条具有低血管阻力，对尿液形成没有贡献。本文讨论了穿过盲鳗肾小球的各种血流途径可能的解剖位置及其功能方式。
