The vascular structure of the kidney of the neotenous axolotl and its metamorphosed counterpart

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Abstract
The renal vascular and glomerular structures of the kidney of neotenous and experimentally metamorphosed axolotls (Ambystoma mexicanum: Amphibia, Urodela) are investigated using light, transmission electron, and scanning electron microscopy of critical-point dried specimens and vascular corrosion casts. The blood vascular system of the kidney in the axolotl is generally similar to that in other urodeles. The glomeruli are comparatively large and distincly ovoid (mean size 267 × 201 μm). Glomerular endothelial nuclei frequently bulge into the vascular lumen. Whereas the lamina rara externa and the lamina densa are quite uniform in diameter, the lamina rara interna shows a very irregular thickness with frequent interposed cellular processes. In the thyroxine-metamorphosed animals, the glomerular surface decreased by a factor of approximately 36%; this was mainly due to the reduction of the glomerular diameter in the direction from vascular to urinary pole. No significant degeneration or new formation of renal tubules was observed during or after metamorphosis. A notable relative decrease in renal volume (approx. 57%) in the metamorphosed forms can be attributed mainly to a reduction in interstitial volume.