Katz U, Hanke W
Zoologisches Institut II der Universität, Karlsruhe, Germany.
J Comp Physiol B. 1993;163(3):189-95. doi: 10.1007/BF00261664.
The acclimation of the clawed toad Xenopus laevis to hyperosmotic solutions of NaCl (balanced solution of sea salt), urea or mannitol was studied. The animals could not be acclimated to salt solutions more concentrated than 400 mosm.1-1. Urea was tolerated till 500 mmol.1-1. Plasma osmolality was always hyperosmotic to the environmental solution, but with diminished osmotic gradient at the highest tolerated solutions. Plasma urea concentration approached 90 mmol.1-1, similar in the three solutions of acclimation. Urine volume was very small under all conditions. Serum aldosterone and corticosterone did not differ significantly, although there was a slight tendency towards lower aldosterone in the NaCl solution. In vivo water uptake in tap water acclimated animals was very small, and was higher in the other groups. Only the salt- and urea-acclimated, but not the tap water and mannitol-acclimated groups responded with a clear increase following injection of oxytocin or theophylline. In vitro urea fluxes were similar and invariable in both directions under all conditions. No significant effect of theophylline was observed. Sodium transport measured by the short-circuit technique in vitro was lower in salt- and mannitol-acclimation conditions, and was stimulated significantly under all conditions in response to serosal oxytocin or theophylline. It is concluded that Xenopus laevis can osmoregulate at a limited range of external solutions. It is limited in the increase of its plasma urea concentration; the transport properties of the skin do not change very much upon acclimation, except for the hydroosmotic response to oxytocin.
研究了爪蟾非洲爪蟾对NaCl（海盐平衡溶液）、尿素或甘露醇高渗溶液的适应性。动物无法适应浓度高于400 mosm·L⁻¹的盐溶液。尿素可耐受至500 mmol·L⁻¹。血浆渗透压始终高于环境溶液，但在最高耐受溶液中渗透梯度减小。血浆尿素浓度接近90 mmol·L⁻¹，在三种适应溶液中相似。在所有条件下尿量都非常少。血清醛固酮和皮质酮没有显著差异，尽管在NaCl溶液中醛固酮有轻微降低的趋势。自来水中适应的动物体内水摄取量非常少，其他组摄取量更高。只有盐和尿素适应组，而不是自来水和甘露醇适应组，在注射催产素或茶碱后有明显增加。在所有条件下，体外尿素双向通量相似且不变。未观察到茶碱有显著影响。用短路技术体外测量的钠转运在盐和甘露醇适应条件下较低，在所有条件下，对浆膜侧催产素或茶碱均有显著刺激作用。得出结论，非洲爪蟾能在有限范围的外部溶液中进行渗透调节。其血浆尿素浓度升高有限；除了对催产素的水渗透反应外，皮肤的转运特性在适应后变化不大。
