Summary
The mechanisms underlying diuresis in the leech have been investigated.
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1.
The time course of the osmotic and ionic concentrations of the primary urine was measured after filling the crop with hypo- or hyperosmotic salt solutions. They were compared with data of blood and final urine, obtained earlier under the same conditions.
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2.
The strong diuresis after feeding is probably due to accelerating primary urine formation rather than to a decrease in reabsorption of primary urine volume.
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3.
The Na+ and K+ concentrations in the primary urine each show a distinct time course after hyper- or hypo-osmotic crop infusion. Cl− concentration always equals the sum of the Na+ and K+ concentrations.
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4.
Assuming that volume change between primary and final urine is negligible, it is calculated that primary urine secretion of Na+ is increased nearly 8 fold after hypo-osmotic crop infusion and 15 fold after hyperosmotic crop infusion, respectively, and secretion of K+ nearly 4 fold in both cases. Thus, during diuresis primary urine flow appears to be generated mainly by Na+-secretion.
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5.
The secretory rate of Na+, K+, and Cl− is not sensitive to the respective blood concentrations.
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6.
The percentage reabsorption of K+ is always higher than that of Na+. However, the percentage and real reabsorption of Na+ after hyperosmotic crop infusion is significantly lower than after hypo-osmotic crop infusion.
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7.
It is suggested that Na+ and K+ secretion and reabsorption are controlled by separate mechanisms.
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Zerbst-Boroffka, I., Wenning, A. & Bazin, B. Primary urine formation during diuresis in the leech,Hirudo medicinalis L.. J Comp Physiol B 146, 75–79 (1982). https://doi.org/10.1007/BF00688719
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DOI: https://doi.org/10.1007/BF00688719