Hypertyrosinemia (HT) is a life-threatening condition caused in large part by the buildup of
tyrosine metabolites and their derivatives. One such metabolite is
succinylacetone (SA), a potent irreversible inhibitor of
heme biosynthesis.
Heme is a key component of numerous
enzymes involved in arterial blood pressure (BP) regulation, including
nitric-oxide synthase (NOS) and its downstream mediator
soluble guanylyl cyclase (sGC). Because NOS and sGC are important regulators of cardiovascular function, we hypothesized that inhibition of
heme supply to these
enzymes by SA would result in the induction of a measurable hypertensive response. Male Sprague-Dawley rats were treated with SA (80 mg x kg(-1) x day(-1) i.p.) for 14 days, resulting in a marked increase in urinary SA and
delta-aminolevulinic acid (P < 0.001 for both parameters) and decreased
heme concentrations in kidney, liver, spleen, and vascular tissues (P < 0.05 for all parameters). After SA treatment, systemic
nitrite/
nitrate excretion was reduced by 72% (P < 0.001), and renal NOS and sGC activities were decreased by 32 (P < 0.05) and 38% (P < 0.01), respectively. SA administration also compromised the ex vivo sensitivity of aorta to endothelium-dependent and -independent vasodilation. Despite these effects, SA treatment failed to induce any changes in BP, as assessed by radiotelemetry. Moreover, BP profiles in the SA-treated animals were less responsive to altered
sodium intake. The present results demonstrate that extended inhibition of
heme synthesis with SA affects hemoenzyme function, albeit without consequent effects on BP regulation and
sodium excretion.