K. C. Hayes

COMPARATIVE LIPID RESPONSE OF FOUR PRIMATE SPECIES TO DIETARY CHANGES IN FAT AND CARBOHYDRATE

Abstract The serum lipid response to long-term feeding of saturated or unsaturated fat with or without dietary cholesterol was compared during three experiments using four species of juvenile monkeys (squirrel, cynomolgus, cebus and spider) born and raised in captivity. When diets containing 10% safflower oil, 10% coconut oil, or high in carbohydrate (48.6 %) with or without 0.1 % cholesterol were fed to cebus and squirrel monkeys for alternate 6 week periods, coconut oil was hypercholesterolemic in both species, but dietary cholesterol further enhanced the hypercholesterolemia only in squirrel monkeys. The effect of the nature of the dietary carbohydrate on serum lipids was examined by feeding these diets continuously to spider monkeys for 36 months while varying the source of the carbohydrate. The results indicated that only coconut oil with sucrose was hyperlipidemic in this species. When cynomolgus and cebus monkeys were fed coconut or safflower oil with or without 0.2% cholesterol, the cynomolgus monkey demonstrated a marked hypercholesterolemia in response to dietary cholesterol and a more moderate response to saturated fat, while the cebus again proved more sensitive to dietary saturated fat than to dietary cholesterol. These data emphasize the interspecies variation between primates with respect to their serum lipid responses to dietary saturated fat, carbohydrate and cholesterol, and identify potential models for study of control mechanisms involved in the regulation of circulating lipids.

Hematological Development of the Infant Squirrel Monkey (Saimiri sciureus)

Hematologic developmental norms from infant squirrel monkeys indicate a relative maturation of the hematopoietic system by 16 weeks. The elevated hemoglobin, hematocrit, red blood cell count, MCV and MCH at birth are followed by a decreasing hemoglobin (decreasing red blood cell count and MCV) until 4 weeks of age. A reticulocytosis then occurs until the hemoglobin level approximates adult concentrations by 16 weeks of age with gradual changes in this as well as hematocrit, red blood cell count, MCV and MCH thereafter. Total leukocytes and segmented neutrophils are elevated at birth and decrease rapidly in the first 2 weeks, reaching stabile values by 16 weeks. An opposite trend is seen with the lymphocyte population. Plasma protein and albumin concentrations show a nadir at 2 weeks of age with the albumin levels stabilizing by 10 weeks and the total protein concentration continuing to increase throughout the 1st year.

Effect of diet on hepatic and intestinal lipogenesis in squirrel, Cebus, and cynomolgus monkeys

Since distinct species differences were found in the serum lipid response of several species of nonhuman primates to dietary fat and cholesterol, in vitro lipogenesis by liver and intestine was studied in four of these species (Cebus albifrons and apella, Macaca fascicularis, and Saimiri sciureus) in order to identify potential differences in the capacity of these tissues to synthesize cholesterol and triglyceride. Comparison of New World cebus and Old World cynomolgus monkeys demonstrated that the cebus monkey exhibited a greater potential for cholesterogenesis in the liver and for total lipogenesis in the jejunum than did the cynomolgus monkey. Proportionately, however, the cynomolgus demonstrated a higher rate of intestinal cholesterol synthesis in vitro relative to hepatic cholesterol synthesis than did the New World species. The feeding of cholesterol with butterfat to squirrel monkeys caused a 94% inhibition of cholesterol synthesis from acetate in liver slices and a 48% inhibition in the ileum. Dietary coconut oil, on the other hand, when compared to safflower oil resulted in a significant increase in the rate of triglyceride synthesis from acetate in liver from cebus monkeys and in jejunum from cebus and cynomolgus monkeys. The possible relationship of these differences in lipogenesis to species differences in the hyperlipidemic capacity of dietary fat and cholesterol is discussed.

Hypercholesterolemia and triglyceride secretion rates in monkeys fed different dietary fats.

The influence of hypercholesterolemia on the triglyceride secretion rate was studied in both squirrel and cebus monkeys fed coconut oil, corn oil, or safflower oil. The triglyceride secretion rate (TGSR) was determined in vivo following the administration of Triton WR1339, which blocks the clearance of very low density lipoprotein (VLDL). Thus, the increase observed in circulating triglyceride after Triton administration presumably reflects hepatic triglyceride (VLDL) secretion in the fasted state. The VLDL-TGSR was lowest in hypercholesterolemic monkeys and highest in those fed unsaturated fat diets and having a low serum cholesterol. In all instances, TGSR was inversely correlated with the plasma cholesterol concentration. While a definitive explanation for these observations must await further investigation, the possibility that circulating low density lipoprotein (LDL) acts to feed back on VLDL secretion is discussed. The decreased TGSR associated with the diet-induced cholesterolemia also implies clearance of VLDL is impaired under these conditions.