1. Renal lymph flow and composition as well as renal haemodynamics and electrolyte excretion were studied in dogs during three experimental periods: control [endogenous antidiuretic hormone (ADH)], water diuresis (low ADH) and during exogenous ADH administration.
2. During water diuresis CPAH and CCr were significantly increased although lymph flow and urinary sodium excretion were unchanged.
3. Infusion of ADH significantly increased renal lymph flow and sodium excretion. However, when compared with values obtained during water diuresis, ADH infusion did not significantly change clearance for p-aminohippurate (CPAH), creatinine (Ccr) and osmolal clearance (Cosm), filtration fraction or net capillary colloid osmotic pressure in dogs forming concentrated urine.
4. It is suggested that a shift of blood flow from vasa recta to outer medullary capillaries, with increased capillary protein leakage and medullary interstitial volume, is responsible for the changes observed in lymph flow and sodium excretion.