THE EFFECT OF NEUROHYPOPHYSEAL HORMONES ON THE PERMEABILITY OF THE TOAD BLADDER TO UREA*

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Abstract
Mammalian neurohypophyseal hormone added to the serosal bathing medium increases the permeability coefficient from 26[plus or minus] 2.5 (SE) x 10-7 cm/sec. to 274[plus or minus] 3.8 (SE) x 10-7 cm/sec. The permeabilities measured simultaneously in the two directions across the membrane with C14-and N15-urea, respectively, were found equal both in the presence and absence of hormone. This indicates that urea moves passively through the bladder. No evidence of self-depression of the permeability to urea was detected with concentrations of urea in the medium up to 50 mmoles. Although this suggests that there is no carrier-mediated transport through the tissue, it would no exclude the possibility of such transport if urea were hydrogen-bonded to the "carrier". Although the hormonal action on urea permeability effects a passive process, its action, nevertheless, is highly specific. This is illustrated by the absence of an effect of the hormone on the permeability of the bladder to thiourea. The increase in permeability of the membrane to urea following hormone can be largely, if not entirely, accounted for by an action of the hormone to increase the permeability of a diffusion barrier at the mucosal surface of the membrane.