Table 3.

Body weight, Na load, water intake, and both water and Na excretions and balances 3 h after injections of four different concentrations of NaCl in young, middle-aged adult, and old rats

	Dose NaCl, M	BW, g	Na Load, μmol	Na Load, μmol/100 g	Water Intake, ml/100 g	UV, ml/100 g	Water Balance, ml/100 g	UNa, μmol/ml	UNaV, μmol/100 g	% Na Load Excreted	Na Balance, μmol/100 g
Young (n = 10)	0.15	340±13*	102±4*	30±1	0.4±0.1*	0.4±0.1	0.0±0.1	128±13	45±11	152±38	−15±11
	0.50	339±13*	338±14*	100±1	0.5±0.1*	0.4±0.1	0.1±0.2	161±12	64±17	65±18	35±17
	1.00	338±14*	676±28*	200±1	1.0±0.2*	0.4±0.1	0.6±0.2*	170±17	62±20	31±10	138±20
	2.00	350±13*	1384±46*	396±2	1.8±0.2*	0.9±0.2	0.9±0.2*	199±23	162±22	41±6	234±22
Middle-aged (n = 14)	0.15	411±10	123±1	30±1	0.2±0.1	0.3±0.1	−0.1±0.1	133±10	33±9	108±30	–3±9
	0.50	410±9	410±9	100±1	0.3±0.1	0.3±0.1	0.0±0.2	187±14	46±15	46±15	54±15
	1.00	404±9	811±20	199±1	0.5±0.1	0.5±0.1	0.0±0.2	180±12	75±11	38±5	123±11
	2.00	416±9	1659±34	399±1	0.9±0.2	1.1±0.1	−0.1±0.2	209±15	210±21	53±5	189±21
Old (n = 12)	0.15	430±10	129±3	30±1	0.1±0.1	0.4±0.1	−0.3±0.1	64±7*	27±6	90±20	3±6
	0.50	432±7	433±7	100±1	0.3±0.1	0.5±0.1	−0.2±0.1	109±8*	53±14	53±14	47±14
	1.00	430±8	859±17	200±1	0.6±0.1	0.8±0.1	−0.3±0.1	113±11*	91±9	45±5	109±9
	2.00	433±7	1737±27	402±1	1.0±0.1	1.1±0.2	−0.1±0.2	163±6*	175±28	43±7	227±27

Values are means ± SE. BW, body weight. Na load, amount of injected sodium. UV, urine volume. UNa, urinary sodium concentration. UNaV, urinary sodium excretion. Na load excreted, UNaV/Na load × 100. There were significant dose-related increases in Na load, water intake, UV, UNa, UNaV, and Na Balance. There were significant dose × age interactions for water intake and water balances.

^*Significantly different from both the other groups, P < 0.01.