Effect of dehydration and rapid rehydration on renal function and on plasma renin and aldosterone levels in the black Bedouin goat

Abstract

Bedouin goats in the extreme deserts of the Middle East are regularly subjected to severe dehydration and possess a capacity to rapidly rehydrate by drinking large volumes of water. Urine flow, glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) in the fully hydrated animals amounted to 0.74±0.4 ml · min⁻¹, 76±29 ml · min⁻¹ and 344±146 ml · min⁻¹ respectively. In goats that were dehydrated to a loss of about 30% of their initial body weight, urine flow dropped to 24% of the value recorded in the hydrated animals and GFR and ERPF dropped to half their level recorded in the hydrated phase. Na and K⁺ excretion decreased in the water depleted goats and further decrease was recorded following drinking. Following drinking the urine flow, GFR and ERPF of the recently rehydrated goats dropped to below the rates recorded in the dehydrated animals. During the 3 h of the continuous recording that followed the drinking, all three rates did not exceed the predrinking level. Plasma renin activity amounted to 0.37±0.32 ng AI·ml⁻¹·h⁻¹ in the hydrated animals. In dehydrated ones it amounted to 4.8±2.8 ng AI·ml⁻¹·h⁻¹ and a further increase was recorded following drinking. Aldosterone in the hydrated goats was 5.5±4.3 ng% and increased to 13.9±2.3 ng% in the dehydrated animal and amounted to 20.1±5.5 ng% 2 h following drinking. It is concluded that the kidney in the Bedouin goat plays a major role in conserving both water and solutes, not only when deprived of water but also following its rapid rehydration.