Nutrient Requirements of Nonhuman Primates: Second Revised Edition

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Nutrient Requirements of Nonhuman Primates: Second Revised Edition, 2003

rhesus macaques were determined at necropsy (Liu and Griffin, 1978). The tissues examined included the cerebral cortex, cerebellum, thalamus and hypothalamus, medulla oblongata, spinal cord, heart (left ventricle), lung, liver, renal cortex, renal outer medulla, renal inner medulla, diaphragm, skeletal muscle (gastrocnemius), and hair-shaved skin. Mean total water concentrations in those tissues (on a fat-free, wet basis) ranged from 75.8% in skin to 86.8% in the medulla oblongata. The mean concentration of intracellular water as a percentage of total tissue water was lowest in the skin (33.2%) and highest in the thalamus and hypothalamus (82.0%). Pivarnik and Palmer (1994) have reported similar data on humans.

Alterations in body-fluid distribution have been reported in rhesus macaques inoculated with Rickettsia rickettsii, the agent that causes Rocky Mountain spotted fever (Liu et al., 1978). There was no change in total body water concentration, but there was a shift of intracellular water to the extracellular space. The shift had little effect on the amount of interstitial fluid but mainly increased plasma volume. However, there were selective alterations in concentrations of water and electrolytes in several tissues with intracellular overhydration of the medulla oblongata. It was suggested that the localized swelling has the potential to depress the cardiovascular and respiratory centers and to lead to circulatory shock and respiratory arrest.

Effects of Activity Restriction

Total body water concentration, extracellular and intracellular distribution, and water intake and excretion were affected by prolonged restriction of the motor activity of rhesus macaques (Zorbas et al., 1997). Over a 90-day period of activity restriction, changes in fluid metabolism could be divided into three phases. Overall, mean total body water concentrations declined from 62.7% to 50.1% of body mass. The decline was associated with a decrease in water intake, an increase in urine excretion, and increased hematocrit and specific plasma resistance.

Effects of Cold

Acclimation to cold results in adjustments of body-fluid distribution (Oddershede and Elizondo, 1980a, 1982). Exposure of six adult male non-cold-acclimated rhesus macaques to a cold environment (6°C, 85% relative humidity) for 35 days resulted in a mean increase in total body water from 66.7% to 70.8% of body mass. During the pre-cold-exposure control period, intracellular, extracellular, and interstitial fluid volumes in relation to body mass were 47.2%, 19.5%, and 15.1%, respectively. Mean increases in these measures during cold exposure were 3.8%, 3.2%, and 1.0% of body mass.

Prosimians generally have a low basal metabolic rate, which makes it difficult for them to deal with a cool environment (Müller, 1983). The slow loris (Nycticebus coucang) has the lowest basal metabolic rate among normothermic primates reported so far, about 40% of the mass-specific mammalian standard (Müller, 1975, 1979; Whittow et al., 1977). Although mainly an inhabitant of tropical rain forests with relatively constant high temperatures, the slow loris has morphologic features of a cold-adapted homeotherm: thick fur, short nose, small ears, stumpy tail, and short, stout limbs. Those features and vascular bundles in the extremities that function as countercurrent heat exchangers (Müller, 1979) limit loss of heat, because of the insulation of fur, the minimum surface area per unit of mass, and redirection of fluids (and the heat they carry) to the body core. Thus, core temperatures can be sustained during moderate cold exposure, even with modest basal heat production.

The slender loris (Loris tardigradus) is found in tropical rainforests but also lives in deciduous forests that experience drought and heat seasonally. It has a long body, a long nose, large ears, very long, thin limbs, and a basal metabolic rate that is about 50% of the mass-specific mammalian standard. When exposed to cold, the slender loris diverts body fluids to maintain a high temperature only in a small body core; large parts of the body are allowed to cool. However, the lower limit of its thermoneutral zone was found to be only 32.5°C, and the slender loris was unable to increase heat production sufficiently to sustain vital functions at low temperatures (Müller et al., 1985). Other findings support the conclusion that this species is better adapted to high than to low temperatures—a circumstance that is consistent with its natural environment.

Effects of Heat and Water Deprivation

Heat acclimation of rhesus macaques from 24°C and 65% relative humidity to 35 days at 35°C and 30% relative humidity was characterized by a fluid shift from interstitial space to the cardiovascular system and the intracellular compartment. Water input via drinking increased from 95 to 118 ml·BW_kg^-1·d^-1, and total water input via drinking, metabolic water, and moisture in food increased from 120 to 140 ml·BW_kg^-1·d^-1. Total body water, determined by tritiated-water dilution, increased by 4.8% during heat exposure (Oddershede and Elizondo, 1980b).

Hamadryas baboons (Papio hamadryas) are found in desert regions of the Horn of Africa and southern Arabia. In contrast with nondesert species, these baboons were able to maintain normal activity after 2 days of water deprivation in a warm environment by conserving blood-plasma volume at the expense of losses from other fluid compartments (Zurovsky and Shkolnik, 1982). Withholding drinking water for 48 hours during midsummer (22-32°C, 70%

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