Hepatic ?1 and ? adrenergic receptors in various animal species

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Abstract
Plasma membranes were isolated from the livers of various animal species representing the four vertebrate classes: Amphibia, Reptilia, Aves and Mammalia. These liver plasma membranes displayed comparable levels of purity as judged by marker enzyme analysis. The activities of the two marker enzymes, 5′-nucleotidase and γ-glutamyltranspeptidase displayed striking, and quite different, species-dependent differences, with no apparent relationship to phylogeny. α1 and β-adrenergic receptors were characterized in isolated liver plasma membranes by radioligand binding techniques. The hepatic β-adrenergic receptor was found to be expressed in all animals studied; the hepatic α1-adrenergic receptor was absent in Amphibia and Reptilia, co-expressed with the β receptor in Aves, and dominant over the β receptor in Mammalia. These results suggest that, in liver, the β-adrenergic receptor is more primitive while the α1-adrenergic receptor is of a more recent phylogenetic origin. It is proposed that the latter may have evolved in conjunction with hepatic sympathetic innervation.