Contrast media induce various factors that may increase vasoconstriction and decrease vasodilatation in the renal medulla, leading to
hypoxia and acute tubular
necrosis known as contrast-induced nephropathy (CIN) that tends to occur in diabetics and patients with preexisting
renal insufficiency.
Contrast media inhibit mitochondrial
enzyme activities and subsequently increase
adenosine through hydrolysis of
ATP. Both catabolism of
adenosine and medullary
hypoxia generate
reactive oxygen species (ROS) that scavenge
nitric oxide (NO). Released along with
endothelin and
prostaglandin from endothelial cells exposed to
contrast media,
adenosine activates the A1 receptor that mainly constricts afferent arteriole at the glomerulus but not the medullary vasculature.
Adenosine also activates the A2 receptor that increases NO production, leading to medullary vasodilatation which is induced by activation of
endothelin-B receptor and
G-protein coupled E-
prostanoid receptor 2, and 4 of
prostaglandin PGE2 respectively as well. Conversely medullary vasoconstriction is mediated by activating
endothelin-A receptor and
G-protein coupled E-
prostanoid receptor 1, and 3 of
prostaglandin PGE2 respectively. The osmotic load of
contrast media increases interstitial pressure and
sodium transport and thus oxygen consumption. Risking
hypoxia, increased medullary oxygen consumption may also result from stimulating Na(+)-K(+)-
ATPase activity by
endothelin-A receptor.
N-acetylcysteine (NAC) scavenges ROS and therefore preserves NO that not only dilates medullary vasculature but also reduces
sodium reabsorption and oxygen consumption, tipping the balance against medullary vasoconstriction,
hypoxia, and thus CIN. While
prostacyclin and its analog,
iloprost, prevent CIN by inducing medullary vasodilatation,
atrial natriuretic peptide (
ANP) may do so by inhibiting
renin secretion.