Thermogenesis, low-protein diets, and decreased development of AFB1-induced preneoplastic foci in rat liver.
The development of hepatocellular, putatively preneoplastic, gamma-glutamyl transpeptidase positive (GGT+) foci and tumors induced by aflatoxin B1 (AFB1) has been shown to be reduced in male F344 rats fed a diet containing 6% protein (as casein). This reduction occurs despite increased energy intake, when compared with animals fed a diet containing 22% protein. Among its many effects, low protein intake is known to increase the proportion of energy intake expended in the form of heat (thermogenesis); thus, this investigation examined the association between the development of GGT+ foci and alterations in indices of thermogenesis induced by feeding varying levels of dietary protein. Five days following the completion of AFB1 dosing, animals were assigned to groups fed 4%, 8%, 12%, 16%, or 22% dietary protein for 6 weeks. Foci development (% liver volume occupied) was markedly reduced in animals fed the low-protein diet (4%, 8%), yet calorie consumption per 100 g body wt was greater. A modest negative linear trend was observed in oxygen consumption with increasing levels of dietary protein intake. Urinary norepinephrine levels were elevated in the groups fed 4% and 8% protein; urinary dopamine and norepinephrine turnover rates in brown adipose tissue were highest in animals fed 4% protein. These results suggest that GGT+ foci development occurs when a "critical level" (approx 12%) of dietary protein intake is reached. Inhibition of foci development at lower levels of protein intake is associated with several indicators of increased thermogenesis.
Department of Agriculatural Chemistry, Faculty of Agriculture, Nagoya University, Japan.
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Horio
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Youngman
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Bell
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Campbell
D016604:Aflatoxin B1 / Q000008:administration & dosage / Q000009:adverse effects*; D000818:Animals; D001833:Body Temperature Regulation; D001835:Body Weight; D002364:Caseins / Q000008:administration & dosage / Q000494:pharmacology; D004044:Dietary Proteins / Q000008:administration & dosage / Q000494:pharmacology*; D004298:Dopamine / Q000652:urine; D004435:Eating; D008099:Liver / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced* / Q000737:chemistry / Q000201:enzymology / Q000652:urine; D008297:Male; D009638:Norepinephrine / Q000032:analysis / Q000652:urine; D009929:Organ Size; D010101:Oxygen Consumption / Q000187:drug effects; D011230:Precancerous Conditions / Q000139:chemically induced* / Q000737:chemistry / Q000201:enzymology / Q000652:urine; D051381:Rats; D011916:Rats, Inbred F344; D005723:gamma-Glutamyltransferase / Q000032:analysis
D002364:Caseins; D004044:Dietary Proteins; D016604:Aflatoxin B1; D005723:gamma-Glutamyltransferase; D004298:Dopamine; D009638:Norepinephrine