Endocrines and Osmoregulation

The renal effects of neurohypophysial hormones in fishes and amphibians are discussed. Injections of arginine vasotocin (AVT) elicit diuresis in fishes, but antidiuresis in amphibians. However, the physiological significance of these hormonal responses remains to be demonstrated. Studies with bioassays and radio-immunoassays on circulating levels of AVT indicate that hypovolemia may be a very potent stimulus for the release of the hormone. Hyperosmotic stimuli may not be as important. In anurans, mesotocin has a glomerular diuretic effect. This neurohypophysial hormone appears to dilate, while AVT constricts, the afferent glomerular circulation in bullfrogs, Rana catesbeiana .

Osmoregulatory Functions of Neurohypophysial Hormones in Fishes and Amphibians

Physiological correlates of basking in amphibians.

Compensatory changes in blood volume following hemorrhage were studied in the toad Bufo marinus. Intact (n = 5), sham operated (n = 3), and animals with destroyed lymph hearts (LH-, n = 6) were bled to 78%, 78%, and 74% of their initial blood volumes, respectively. Post-hemorrhage changes in blood volume were estimated by analyzing changes in hematocrit and concentration of an injected plasma volume marker, Evans blue. Analysis of both markers indicated significant replacement of plasma volume following hemorrhage in the intact and sham animals. An acute compensation period lasting 10-25 min resulted in recovery to between 91% and 108% of initial blood volume. This replacement of plasma volume occurred without concomitant washout of an injected extracellular fluid (ECF) volume marker, SCN⁺. Therefore, the compensation resulted from redistribution of ECF rather than mobilization of intracellular fluid. Animals with destroyed lymph hearts showed no evidence of acute replacement. The animals in this group ex...

Charles R. Kleeman

Papers

Neurohypophysial function in the toad Bufo marinus.