Joseph Kemnitz, Ph.D.

Primate Research Center
1220 Capital Court
Madison, WI 53715
608-263-3500
kemnitz@primate.wisc.edu

Emphasis Group:
Human Nutrition

Principal Research Interest:
Regulation of Energy Balance and the Processes of Aging.

Research Summary:
My research is directed toward understanding the neurobehavioral and hormonal mechanisms that control food intake and energy expenditure and to the consequences of caloric imbalances for physiological well-being. Most of my projects utilize rhesus monkeys, because these nonhuman primates share so many important characteristics with our own species and can be studied in a careful, controlled manner.

Recent efforts have focused on changes that occur in middle and late life. Rhesus monkeys achieve adult body size by approximately eight years of age. Males are, on average, 25% heavier than females during adulthood in large part due to the stimulating effects of testicular androgens on muscle development. During middle age, monkeys of both sexes tend to add body fat and lose lean body mass. Food intake among adults is very variable, although average intakes of individuals are quite consistent. Females show systematic changes in food intake during menstrual cycles that reflect an inhibition of eating by estrogen.

Some middle-aged monkeys are markedly obese. Excess body fat accumulates predominantly in the abdominal region. Obese monkeys do not seem to eat more than nonobese animals, but their physical activity is dramatically lower. We are currently investigating the causes and consequences of obesity in rhesus monkeys in more detail. These projects include evaluations of metabolic rate in obese and lean monkeys and studies of how certain hormones may act on the hypothalamus to modulate food intake and energy expenditure.

Obese monkeys provide a good model for studying certain complications of human obesity. For example, there are similar abnormalities in blood glucose regulation, blood pressure and hormone metabolism in the obese of both species. Obese monkeys have elevated insulin levels and often impaired glucose tolerance. Their ability to maintain normal blood glucose levels declines as they get older, and some obese monkeys become diabetic in later life. We suspect that obesity accelerates this age-related deterioration of glucose tolerance.

The relationship between energy balance and the processes of aging is being assessed prospectively in a multidisciplinary study of approximately 70 rhesus monkeys. Half of the animals are being fed a moderately reduced amount of a nutritious diet, while the control monkeys are allowed to eat ad libitum. It was hypothesized that the food restricted group would exhibit slower rates of change in certain characteristics of aging, including blood glucose regulation. Indeed, the restricted monkeys have greater insulin sensitivity, lower glucose concentrations and improved glucose tolerance. Their metabolism of energy is also affected. Such effects of reduced food intake in these restricted primates are consistent with the retardation of disease and extension of lifespan that has been demonstrated for food restricted nonprimate species. If the phenomenon can be confirmed in primates, there would be a clearer potential for manipulating the course of aging by nutritional intervention in humans.

My work is conducted at the Wisconsin Regional Primate Research Center, one of seven such centers nationally established by the NIH. The Center has nearly 1000 rhesus monkeys and about 300 primates of several other species. There are typically about 10-15 postdocs, students and technicians working in my lab. We enjoy several active collaborations with other laboratories at the Primate Center and elsewhere on campus.

Representative Publications:

Raman A, Baum ST, Colman RJ, Kemnitz JW, Weindruch R, Schoeller DA. Metabolizable energy intake during long-term calorie restriction in rhesus monkeys. Exp Gerontol. 2007 Oct;42(10):988-94.

Zhou R, Bruns CM, Bird IM, Kemnitz JW, Goodfriend TL, Dumesic DA, Abbott DH. Pioglitazone improves insulin action and normalizes menstrual cycles in a majority of prenatally androgenized female rhesus
monkeys. Reprod Toxicol. 2007 Apr-May;23(3):438-48.

Raman A, Ramsey JJ, Kemnitz JW, Baum ST, Newton W, Colman RJ, Weindruch R,Beasley MT, Schoeller DA. Influences of calorie restriction and age on energy expenditure in the rhesus monkey. Am J Physiol Endocrinol Metab. 2007 Jan;292(1):E101-6.

Raman A, Colman RJ, Cheng Y, Kemnitz JW, Baum ST, Weindruch R, Schoeller DA. Reference body composition in adult rhesus monkeys: glucoregulatory and anthropometric indices. J Gerontol A Biol Sci Med Sci. 2005 Dec;60(12):1518-24.