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.
Horio
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Department of Agriculatural Chemistry, Faculty of Agriculture, Nagoya University, Japan.
Youngman
L D
LD
Bell
R C
RC
Campbell
T C
TC
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