Effect of Water and Saline Load on Urinary Output in Healthy Undergraduate Medical Students

Abstract

Water and electrolyte balance is a vital homeostatic function. Their excretion depends on various factors –state of hydration, plasma osmolarity etc. There are rare reports on effect of hypertonic solution on urinaryoutput. Therefore, the study aimed at investigating the effect of water or saline (especially the hypertonic)load on urinary output (UO) in healthy undergraduate male medical students (17-20 years). They (n=20)were randomised into 4 equal groups: control, water, normal and hypertonic saline (1.8%). The study wasa part of undergraduate practical conducted under controlled conditions in the Physiology Department,BPKIHS. The day before the experiment, all of them were given same instructions. Next day, the experimentalgroups drank water/saline solution 12 ml/kg. Then the UO was measured ½-hourly. A non-parametric –Friedman test was used for intra- and inter-group differences in UO and specific gravity. The data arepresented as median (range). In water group the 60-min UO was significantly higher than the 30-min UO[178.5 (24-415) vs. 22.5 (21-81) ml, p<0.05]. This group also had significantly higher UO than the control at90-min [84 (20-250) vs. 19 (18-23) ml, p<0.05)]. The UO of normal-saline group was significantly higherthan that of control at 90-min [40 (22-250) vs. 19 (18-23) ml, p<0.05]. There was no significant difference inspecific gravity. The water and normal saline loads were adequate to elicit physiological response, thehypertonic solution was not strong enough to show significant physiological response suggesting need ofsaline load to be more than twice of the plasma osmolarity.Key Words: homeostasis, water-electrolyte balance, salt load, water load.