Influence of dietary histidine on basophil release, circulating concentration, and urinary excretion of histamine in domestic felines

Dietary histidine has been shown to elevate circulating free histidine and plasma histamine concentration in murine models as much as 6- fold. Bladder mastocytosis is a hallmark of feline interstitial cystitis, and histidine is stored in mast cells and converted to histamine for signaling and inflammation by the enzyme histidine decarboxylase. Elevated dietary histidine may represent a risk factor for heightened mast cell responses. Nine healthy adult female shorthair cats were used in random crossover experiment with fixed treatment sequences to test the effects of dietary histidine (0.6, 1.0, and 1.4% DM) on histamine in blood and urine. The dry-extruded test foods were fed in sufficient amounts to maintain ideal body weight. Each experimental period was preceded by a 7-day wash out period, in which the 0.6% histidine diet was fed, followed by a 14-day feeding period of the appropriate food. Two 24-hr total urine collections were performed (d13: acidified, day 14: un-acidified; immediately iced) and blood was collected on day 14. Dry matter intake (P≥0.09) and BW (P≥0.58) were not affected by treatment. Plasma histidine concentration increased with dietary supply of histidine (linear, P=0.02). Urine output (P≥0.42), NH3 (P≥0.53) and titratable acidity of urine (P≥0.31) were similar across treatments. However, urine pH was lower in cats fed 1.4% histidine compared with 0.6 or 1.0% histidine (quadratic, P=0.02). Urinary histamine:creatinine was greater for the 1.4% histidine treatement (linear, P=0.03) compared to other diets, whereas urinary histamine concentration (P=0.17) and excretion (P≥0.68) and plasma histamine concentration (P≥0.17) were unaffected by treatment. Differences were not detected among treatments in total histamine, cellular + noncellular,(P≥0.18) or antigen-induced histamine release (P≥0.65) in whole blood. Increase in dietary histidine elevates circulating concentrations of histidine without affecting circulating concentrations of histamine or antigen-induced histamine release in whole blood. However, urinary histamine excretion may be responsive to dietary histidine supply.