Ontogeny of rat hepatic adrenoceptors.
Hepatic alpha-1, alpha-2 and beta-2 adrenoceptors were characterized during development of the rat through Scatchard analysis of [3H]prazosin, [3H]rauwolscine and [125I]pindolol binding to liver membrane preparations. Major changes in adrenoceptor numbers occur shortly before birth at weaning. The fetal rat liver is characterized by a large number of alpha-2 adrenoceptors, which falls 10-fold by birth. The number of hepatic beta-2 adrenoceptors decreases gradually during development, and is lower at all times than the number of alpha-1 and alpha-2 adrenoceptors. The developmental profile of the hepatic alpha-1 adrenoceptor is biphasic: there is a 2 to 3-fold fall in alpha-1 adrenoceptor number at birth and a 3- to 5-fold rise at weaning. While absolute numbers of alpha-1 and beta-2 adrenoceptors do not correlate precisely with reported actions of epinephrine and norepinephrine on hepatic metabolism during ontogeny, the increasing ratio of alpha-1/beta-2 hepatic adrenoceptors may contribute to the conversion from predominantly beta effects of catecholamines reported in fetal and suckling rat liver to the predominantly alpha-1 effects that are well documented in the adult male rat.
McMillian, MK; Schanberg, SM; Kuhn, CM
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