Selective mouse breeding for short ethanol sleep time has led to high levels of hepatic aromatic hydrocarbon (Ah) receptor

Abstract

Following a selective breeding program of heterogeneous mice for more than 30 generations, SS (“short sleep”) and LS (“long sleep”) lines have been developed on the basis of their sleep times when challenged with a single intraperitoneal dose of ethanol. The aromatic hydrocarbon responsiveness ( Ah) locus encodes the Ah receptor, which regulates the induction of certain drug-metabolizing enzymes by polycyclic aromatic compounds such as 3-methylcholanthrene and tetrachlorodibenzo- p-dioxin. The C57BL/6 inbred mouse strain (B6; Ah b/ Ah b) has a high-affinity Ah receptor, while the DBA/2 inbred mouse strain (D2; Ah d/ Ah d) has a low-affinity Ah receptor. We show here that the SS inbred mouse line exhibits markedly elevated hepatic levels of the high-affinity Ah receptor, while the LS outbred mouse line contains the low-affinity Ah receptor. Among progeny of (B6D2)F 1 × D2 backcross, the b/ d heterozygote (having the high-affinity Ah receptor) was found to be several times more resistant than the d/ d homozygote to a single dose of intraperitoneal ethanol. The D2.B6- Ah b congenic line is also several times more resistant to intraperitoneal ethanol than the B6.D2- Ah d congenic line. We found that the waking blood ethanol levels are the same in b/ d and d/ d mice, suggesting that the relative ethanol resistance in b/ d mice cannot be explained on the basis of a difference in central nervous system sensitivity. There are no differences between SS and LS mice or between b/ d and d/ d mice with regard to (i) blood acetaldehyde levels after a single intraperitoneal dose of ethanol, or (ii) hepatic alcohol dehydrogenase activities. There is a difference in the rate of ethanol elimination: SS more rapid than LS; b/ d more rapid than d/ d. Although SS mice have lower hepatic aldehyde dehydrogenase activities (cytosolic, mitochondrial low- K m ; and mitochondrial high- K m forms) than LS mice, b/ d and d/ d do not show this difference. These data suggest that a selected mouse breeding program, based on resistance to a single intraperitoneal dose of ethanol, selects concurrently for the hepatic high-affinity Ah receptor. This selective advantage cannot be explained on the basis of changes in alcohol dehydrogenase or aldehyde dehydrogenase activities and might provide insight into the nature of the endogenous ligand for the Ah receptor.