Water-balance response to salt loads in the toad Bufo bufo: independence of hypophysial pars nervosa function.

1. In water, injection of 1 ml of 1 mol/l NaCl/100 g body mass increased the rates of cutaneous water uptake and reduced the rates of bladder urine accumulation both in unoperated and sham operated controls and in toads with denervated or extirpated neuro-intermediate lobe. 2. This initial antidiuretic effect of the salt load gradually changed to a diuretic effect, when the volume expansion caused by cutaneous water uptake overrode the effect of increased osmolarity. 3. In a saturated atmosphere, injections of 0.3 or 0.5 ml of 0.7 mol/l NaCl/toad (mean body mass 33 g) reduced urine accumulation. Only to the largest load was the antidiuretic response significantly smaller in the toads with denervated or extirpated neuro-intermediate lobe. 4. It is argued that the reduced antidiuretic response was due to interference with pars distalis function rather than caused by lack of pars nervosa function.