Adrenocorticotropin inhibits nitric oxide synthase II mRNA expression in rat macrophages

During hemorrhagic shock there is a massive overproduction of nitric oxide (NO). In such conditions, the intravenous (i.v.) injection of melanocortin peptides in nanomolar amounts produces a long-lasting restoration of cardio vascular and respiratory functions associated with the normalization of NO blood levels. To clarify the mechanism of such melanocortin-induced inhibit ion of NO overproduction, the influence of the adrenocorticotropin fragment 1-24 [ACTH(1-24)] on the NO synthesizing activity of rat macrophages was s tudied in vitro. Nitrite production, an indicator of NO synthesis, was meas ured in the supernatant of rat macrophages whose inducible NO synthase (NOS II, iNOS) had been stimulated by the addition of S. enteritidis lipopolysa ccharide (LPS, 50 mu g/ml). ACTH-(1-24) (25, 50 and 100 nM) inhibited nitri te production when incubated together with LPS, but had no effect when appl ied 6h after LPS. Further, the effect of ACTH-(1-24) on the expression of i NOS mRNA in rat macrophages activated with LPS was studied by means of a re verse transcriptase-polymerase chain reaction assay. ACTH-(1-24) (25, 50 an d 100 nM), applied together with LPS, dose-dependently suppressed iNOS gene activation. The present data suggest that the melanocortin-induced normali zation of NO blood levels during hemorrhagic shock is due, at least in part , to a direct inhibition of iNOS induction, at the level of mRNA transcript ion.