Plasma concentrations and urinary excretions of
nitrite plus
nitrate (NOx) increase in heifers after
endotoxin-induced
nitric oxide synthase activation. The rise can be enhanced by administration of
arginine, the substrate for the production of
nitric oxide, whose effects may be modified by the
iron status. In 10-week-old veal calves (six Simmental x Red Holstein)
arginine (0.5 g/kg
body weight for 6 h) was intravenously infused. At 2 h after the start of the infusions
Escherichia coli endotoxin O26:B6 (2 microg/kg
body weight) was intravenously injected. This caused a rise of rectal temperature, heart rate, respiration rate, and of urinary NOx excretion, but not of plasma NOx concentrations, in contrast to the experience with older cattle to which the same amounts of
arginine were infused before and during
endotoxin administration. In 8-week-old veal calves (18 Simmental x Red Holstein) the question of whether oral supplementation with
arginine and
iron modifies NOx responses to
endotoxin (2 microg/kg) was also investigated. The calves were divided between three groups (GrA-, GirA+, GrC) and before
endotoxin injections GrA- was fed 0.5 g
arginine/kg for 4 days, GrA+ was fed 0.5 g
arginine/kg for 4 days plus 80 mg
iron/kg milk for 2 weeks, whereas GrC was not supplemented with
arginine or
iron.
Iron supplementation increased plasma
iron concentrations and
arginine supplementation increased plasma
arginine and
urea concentrations and urinary
urea excretion. Ensuing administration of
endotoxin enhanced plasma tumour
necrosis factor-alpha concentrations, rectal temperature, heart rate, and respiration rate, but not plasma NOx concentrations in GrC and GrA- and only transiently and slightly increased plasma NOx concentrations in GrA+ but did not affect urinary NOx excretions. In conclusion, the expected stimulation of NOx responses to
endotoxin by intravenous
arginine infusion appears to be much weaker in young veal calves than in older cattle. The NOx responses in young veal calves were not modified if
arginine was orally administered and plasma NOx were barely enhanced by combined oral supplementation of
arginine and
iron.