relative humidity) induced dehydration. Total body water was determined with tritiated-water dilution, and plasma volume was determined with Evans blue dilution (before and after water deprivation). The procedure was repeated six or seven times in each of three animals over a 2-year period. After 2 days of water deprivation, 10% of body mass and 12.5% of body water, but only 4% of plasma volume, were lost. The ability to sustain plasma volume was related to an increase in plasma colloidal osmotic pressure through efficient retention of albumin and an increase in the rate of albumin synthesis (Zurovzky et al., 1984).
Adolescent male baboons (Papio cynocephalus and P. anubis) weighing 11.9-16.5 kg were subjected to water deprivation for 64-68 hours, and the effects of dehydration on blood and plasma volumes, plasma constituents, and weight were measured (Ryan and Proppe, 1990). In addition, the effect of interaction of increased environmental temperature (38-42°C vs 22-24°C) and dehydration on hindlimb blood flow was explored. Plasma osmolality and concentrations of blood hemoglobin and plasma sodium and total proteins were significantly increased by dehydration. Blood volume, plasma volume, and weight were significantly decreased. Dehydration attenuated the cutaneous vasodilatory response to heat stress in the hindlimb, and studies of intravenous fluid replacement suggested that the attenuation was associated with a local mechanism in the vascular smooth muscle cell that was triggered by interstitial-fluid volume depletion.
Crab-eating macaques (Macaca fascicularis) are found along the southeastern coast of the Asian continent and on Southeast Asia islands. On the Indonesian island of Bali, the species has adapted to a region of considerable rainfall (72-98 mm per month) and to a region with a dry season when there is no water in the rivers and monthly rainfall is only 7-12 mm. They were free-ranging monkeys, so it was possible to study shifts in body fluids in response to dehydration only by collecting single blood samples from each animal. Hematologic data on 85 crab-eating macaques in the two regions revealed that blood-plasma protein, creatinine, and sodium ion concentrations were increased in monkeys in the region with low water supply (Takenaka, 1986).
The morphology and behavior of the slow loris equips this species better for dealing with an occasional cool environment as opposed to a hot one. It has a thermal neutral zone between 24-33°C (Müller, 1975), and exposure to an environmental temperature above 35°C usually leads to a rapid rise in rectal temperature (Müller, 1979). Although respiration rate increased to 140 breaths·min-1 at an ambient temperature of 40°C, evaporative cooling at 35°C was sufficient only to dissipate about 50-60% of metabolic heat production (Müller, 1983). The potto (Perodicticus potto) exhibits similar limitations (Hildwein and Goffart, 1975). In contrast, the respiration rate of the slender loris at an environmental temperature of 35°C increased to 200-300 breaths·min-1, and about 80% of metabolic heat production was dissipated by evaporation (Müller et al., 1985). When the water content of surrounding air (75% relative humidity) and ambient temperatures (35°C) were high, the efficiency of evaporative cooling was reduced. However, evaporative cooling was supported by a cardiovascular response that increased transport of body heat from the core to the surface. As a consequence, deep-rectal temperatures rose only slightly above ambient temperature, even after prolonged heat exposure.
Water to meet requirements comes from three sources: free or liquid water, as in dew, rain, snow, terrestrial and arboreal pools, streams, and lakes; preformed water in food; and metabolic water from oxidation of organic compounds in body tissues.
What it eats, ambient temperatures and humidity, activity, and other factors influence the amount of water that a primate drinks. Maintenance of body water balance is the ultimate homeostatic objective. Diets low in moisture or high in fiber, salt, sodium bicarbonate, or protein will increase water consumption (Harris and Van Horn, 1992). Increased air temperatures and aridity will increase water loss and the amount of water consumed for replacement. Some conditions can induce abnormal water intake. A deficiency of n-3 fatty acids in rhesus macques was shown to result in polydipsia, even though the kidneys retained their ability to concentrate urine and there was no evidence of diabetes insipidus (Reisbick et al, 1990, 1991).
Although water, consumed as such, is the major water source for humans in large areas of the world, much of the human water intake in the United States comes from consumption of beverages, such as soft drinks, juices, milk, tea, and coffee (Askew, 1996). Nonhuman primates in the wild drink from running and standing water sources, either by crouching and sipping, by dipping their hand in the water and drinking from their hand or fingers, or by using chewed leaves as sponges to soak up and direct water into the mouth (Angus, 1971). They also have been observed licking moist rocks and plants moist with dew or rain (Nishida, 1980). In a study of free-ranging New World monkeys, mantled howlers (Alouatta palliata) were never seen drinking from terrestrial water sources but rather drank from arboreal cisterns (such as depressions at junctures of tree limbs and trunk) during the wet season. During the dry season, when arboreal cisterns were empty, the howlers