William H. Karasov, Ph.D.

Room 221 Russell Laboratories
1630 Linden Drive
Madison, WI 53706
608-263-9319
wkarasov@wisc.edu

Emphasis Group:
Animal Nutrition

Principal Research Interest:
Regulation and adaptation of digestive tract structure and function to altered feeding rate and diet composition; effects of plant secondary metabolites on herbivore physiology and feeding; nutritional ecology of wild herbivores.

Research Summary:
Our broad research objectives are to understand the physiological mechanisms allowing for effective use of food, and the relation of those processes to wildlife ecology, medical biology, and agriculture.

Past studies with mammals, birds, reptiles, amphibians, and fish have focused on changes in gut structure and function concomitant with, and possible permissive for, changes in diet and intake rate. Findings included changes in specific transport mechanisms for sugars, amino acids, and vitamins in animals following changes in levels of these nutrients in the diet. Studies of regulation of intestinal absorption have also focused on cellular mechanisms of regulation, such as altered electrochemical gradients for Na-coupled transport across the brush border membrane, altered basolateral transport, and paracellular transport. More recently, we are studying modulation of digestive enzyme levels, and the manner in which digesta retention time is altered to maintain digestive efficiency. Future studies will emphasize pathways of passive absorption of hydrophilic compounds.

Anti-nutritive properties of food are also an important determinant of diet choice and intake rate. In our studies with wild herbivores eating wild foods, plant secondary metabolites had modest or no effect on digestive functions. Their most important effects were post-absorptive. Herbivores limited their intake of food to avoid exceeding a threshold intake of xenobiotic chemical, and they experienced losses of energy and nitrogen in the course of detoxication and excretion of the chemical. Future studies will focus on the physiological bases for the apparent thresholds, and on the adaptability of herbivores to changing levels of plant secondary metabolites.

Representative Publications:

Chen TH, Gross JA, Karasov WH. Adverse effects of chronic copper exposure in larval northern leopard frogs (Rana pipiens). Environ Toxicol Chem. 2007 Jul;26(7):1470-5.

Lavin SR, McWhorter TJ, Karasov WH. Mechanistic bases for differences in passive absorption. J Exp Biol. 2007 Aug;210(Pt 15):2754-64.

Gross JA, Chen TH, Karasov WH. Lethal and sublethal effects of chronic cadmium exposure on northern leopard frog (Rana pipiens) tadpoles. Environ Toxicol Chem. 2007 Jun;26(6):1192-7.

McWhorter TJ, Karasov WH. Paracellular nutrient absorption in a gum-feeding new world primate, the common marmoset Callithrix jacchus. Am J Primatol. 2007 Dec;69(12):1399-411.