Endocrine and neural control of amphibian renal functions

Three aspects of amphibian renal functions were considered. 1) The neurohypophysial hormone, arginine vasotocin (AVT), is diuretic in lungfishes, but is antidiuretic in amphibians. AVT probably produces diuresis in fishes by increasing systemic blood pressure and, hence, glomerular filtration rate. Receptors for AVT in early amphibians may have become more numerous or sensitive in the preglomerular circulation than in the peripheral vasculature. AVT could then produce glomerular antidiuresis. Tubular receptors to AVT also developed to provide better control of urine volume during terrestrial adaptation. In our investigations only glomerular antidiuresis was produced by AVT in the mud puppy whereas bullfrogs responded to AVT with both glomerular and tubular antidiuresis. 2) Although exogenous AVT can produce antidiuresis in amphibians, alpha-adrenergic neural mechanisms also appeared to play an important role in glomerular and tubular functions in the bullfrog. 3) Mesotocin, the amphibian neutral neurohypophysial hormone, produces glomerular diuresis in the amphibians studied. However, whether it has a physiological role in regulating amphibian renal function remains unclear.