干旱区生态环境知识资源中心

Severely dehydrated Bedouin goats replenish their water deficit by drinking copiously. Their urine flow, that amounts to only 0.41+/-0.10 ml/min prior to the drinking drops to about half this value immediately after drinking is completed. It remains lower than, or similar to the pre-drinking value for a long period. A retarded plasma renal flow and impeded rate of glomerular filtration were found to underlie the reduction in urine flow in the newly rehydrated goat. When dehydrated goats were injected with 1 mg/kg of propranolol, and then allowed to drink to satiety, their urine bow increased. Half an hour after drinking it amounted to 1.25+/-0.07 ml/min, and 30 min later, to twice this value. The rates of the renal plasma flow and glomerular filtration also increased compatibly. Propranolol is known to be a highly potent blocker of effects induced by excitatory responses on the renal nerve. Presumably, the administration of propranolol eliminated a sympathetic stimulus that in control goats suppresses the rate of renal blood flow and consequently also of glomerular filtration. As plasma arginine vasopressin levels in the dehydrated Bedouin goats is reported to drop abruptly with the onset of the drinking, it is suggested that B adrenergic activity, rather than endocrine mechanisms, plays the major role in modulating renal function in newly rehydrated Bedouin goats. Under natural conditions it helps conserve the water consumed by the goat for periods when the animal is grazing in the desert far from a drinking site.