Ontogenesis of mRNA levels and binding sites of hepatic α-adrenoceptors in young cattle

Abstract

Catecholamines affect hepatic glucose production through (α- and β 2-) adrenoceptors (AR). We studied mRNA abundance and binding of hepatic α-AR in pre-term (P0) calves and in full-term calves at day 0 (F0), day 5 (F5) and day 159 (F159) to test the hypothesis that gene expression and numbers of hepatic α-AR in calves are influenced by age and associated with β 2-AR and selected traits of glucose metabolism. mRNA levels of α 1- and α 2-AR were measured by real time RT-PCR. α 1- and α 2-AR numbers (maximal binding, B max) were determined by saturation binding of ( 3H)-prazosin and ( 3H)-RX821002, respectively. α 1- and α 2-AR subtypes were evaluated by competitive binding. α 1A-AR mRNA levels were lower in P0 than in F0, F5 and F159 and α 2AD-AR mRNA levels were lower in F159 than in P0, F0 and F5, while α 2C-AR mRNA levels increased from P0 and F0 to F5 and F159. B max of α 1-AR increased from P0 to F5, then decreased in F159. B max of α 2-AR decreased from F0 to F159. B max of α 1-AR was positively associated with mRNA levels of α 1A-AR ( r = 0.7), B max of β 2-AR ( r = 0.5) and negatively with hepatic glycogen content ( r = −0.6). B max of α 2-AR was negatively associated with B max of β 2-AR ( r = −0.4). In conclusion, mRNA levels and binding sites of α 1- and α 2-AR in calves exhibited developmental changes and were negatively associated with hepatic glycogen content.