The effect of hormones and of an osmotic gradient on the structure and properties of mammalian foetal urinary bladder in vitro.

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Abstract
Water and isotope fluxes were measured by incubating urinary bladders of fetal pigs and sheep in vitro in the presence and absence of a concentration and osmotic gradient. The structure of the urinary bladder of fetal pigs under various conditions was studied by EM. Its ultrastructure was closely similar to that of fetal sheep. Antidiuretic hormone (ADH) (0.2 u[standard units] ml-1) enhanced the enlargement of intercellular spaces caused by dilute mucosal medium in pig bladders; prolactin (1 u .cntdot. ml-1) prevented osmotic dilatation of the intercellular spaces. The hydraulic conductivity was estimated to be 0.5 .times. 10-7 cm .cntdot. s-1 atm-1 in sheep and pigs at about 100 days gestation; the ratio of osmotic to diffusional permeability in the presence and absence of ADH, was 2.1 and 1.6, respectively. These are similar to the values found in fish gills. Prolactin reduced bulk flow of water to zero in 7 out of 8 bladders investigated. Incubation with ADH or vasotocin (55 mu .cntdot. ml-1) in the presence of prolactin restored water flux to 22% and 45% of control values, respectively. There was no significant net flux of Na from mucosa to serosa in pig bladder except in the presence of prolactin. No net flux of Na occurred from mucosal to serosal side of pig or sheep bladders in the presence of an adverse electrochemical gradient, although in sheep the permeability ratio was significantly greater than 1. The diffusional flux ratio for water remained unity under all conditions; vasotocin increased unidirectional fluxes and prolactin reduced them. The flux ratios were unaffected by the direction of bulk fluid flow, probably because diffusion was rapid compared to flow; the ratio of diffusional flux to volume flow was between 11 and 18.