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Subclinical Ammonia Toxicity in Steers: Effects on Blood Metabolite and Regulatory Hormone Concentrations^1,2,3,4,

North Carolina State University, Raleigh 27695-7621

Abstract

The effects of subclinical NH₃ toxicity on circulating and regulatory hormone concentrations were investigated in seven Hereford steers. Ammonium chloride (NH₄CL) was infused via a right jugular vein catheter at a rate of 12 µmol NH₄Cl·kg BW^–1·min^–1 for 240 min. This was preceded (PRE) and followed (POST) by saline infusions of 120 and 180 min, respectively. Blood samples were taken at 20-min intervals via a left jugular vein catheter. Metabolite and hormone concentrations during NH₄Cl and POST periods were compared to PRE values using the Student's t-test procedure. Plasma NH₃ was elevated rapidly (P < .001) and peaked at 503 µg/dl 220 min into NH₄Cl infusion. Plasma urea-N and glucose increased (P < .001) 39 and 12%, respectively, during NH₄Cl infusion and remained elevated 180 min POST. Whole blood L-lactate concentrations peaked (P < .05) at 18% above PRE between 160 and 240 min into the NH4C1 infusion and gradually returned to PRE values, whereas pyruvate levels were not altered (P > .10). Plasma nonesterified fatty acids peaked (P < .001) at 94% above PRE levels 40 min into NH₄Cl infusion, thereafter declining to PRE concentrations. Whole blood acetoacetate and ²-hydroxybutyrate concentrations were not altered (P > .10) by NH₄Cl administration. Plasma insulin concentration decreased (P < .05) 26 to 46% during NH₄Cl infusion and increased (P < .05) 89 to 122% during POST. Plasma glucagon levels were not altered by NH₄Cl infusion, so molar insulin:glucagon ratio changes resembled those of insulin. Plasma epinephrine, norepinephrine and dopamine did not vary (P > .10) with treatment. These results support the hypothesis that the hyperglycemia observed during hyperammonemia may result from an under-utilization of glucose by insulin-sensitive tissues.

¹ Paper No. 11,220 of the Journal Series of the North Carolina ARS, Raleigh 27695-7601. The use of trade names in this publication does not imply endorsement by the North Carolina ARS of the products named, or criticism of similar ones not mentioned.

² Data are taken from a dissertation submitted by J. M. Fernandez in partial fulfillment of the requirements for the degree of Ph.D. in Anim. Sci.

³ A preliminary report was presented at the 70th Annu. Mtg. of the Fed. of Am. Soc. for Exp. Biol., St. Louis, MO, April 1986.

⁴ The skilled technical assistance of Helen Bartlett is gratefully acknowledged. The authors also wish to thank Sharon Ray for the care of the animals, and Dr. Chance of Lilly Research Laboratories for providing bovine glucagon and insulin standards used in the radioimmunoassays.

⁵ The Dept. of Anim. Sci. and the Interdepartmental Nutr. Prog.

⁶ Present address: Am. Inst. for Goat Res., Langston Univ., Langston, OK 73050.

⁷ To whom correspondence should be addressed.

⁸ Dept. of Poult. Sci.