Effects of cyclic adenosine 3′,5′-monophosphate on amino acid transport and incorporation into protein in the rat aorta

Abstract

To assess the effects of cyclic AMP on amino acid transport and incorporation into aortic tissue protein, rat aortic rings were incubated with the cyclic AMP analog, N6-monobutyryl cyclic AMP (MBcAMP), the phosphodiesterase inhibitor, 3-isoburyl-1-methylxanthine (MIX), and radiolabeled amino acids. Subsequently, the aortic rings were homogenized in 5% trichloroacetic acid (TCA) and processed for liquid scintillation counting. Radioactivity present in the TCA supernatant following centrifugation was used to estimate amino acid transport. TCA-precipitable radioactivity was used as a measure of amino acid incorporation into protein. MBcAMP induced an increase in the uptake of [3H]α-aminoisobutyric acid into aortic rings and an increase in the incorporation of radiolabeled proline and leucine into TCA-precipitable protein. Similar effects were observed with low concentrations of MIX (0.025–0.25 mM); however, at higher concentrations of MIX, there was an attenuation of the effect or frank inhibition. Maximum stimulation of transport was observed within 90–120 min of the addition of MIX or MBcAMP to the incubation medium, whereas the effect on amino acid incorporation was not detectable until after 12 h of exposure to MIX or MBcAMP. The effects of cyclic AMP on transport were observed in both the tunica media and the tunica adventitia, whereas the effects on amino acid incorporation into protein were observed only in the tunica media. These data are consistent with a possible role for cyclic AMP in promoting changes in the tunica media that could lead to the development of vascular hypertrophy.Key words: N6-monobutyryl cyclic AMP, 3-isobutyl-1-methylxanthine, vascular smooth muscle.