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Influence of Adrenergic Blockage upon Some Endocrine and Metabolic Parameters in a Stress-Susceptible and a Fat Strain of Swine¹

Iowa State University, Ames 50010

Abstract

Thirty-six 90-kg live weight swine, 18 from a genetically selected stress-susceptible strain and 18 from a genetically selected fat strain, were catheterized via the anterior vena cava. Six pigs from each strain were given phenoxybenzamine, another six were given propranolol and six individuals of each strain were used as controls. After infusion of the blocking agents, the animals were subjected to 5 min. of induced physical exercise.

Physical exercise significantly (P<.01) increased plasma cortisol, glucose and lactate in both strains. The stress-susceptible swine revealed a significant (P<.01) blood pH decline in response to stress while pigs from the fat strain maintained a relatively constant blood pH. Fat-strain pigs had lower plasma lactate and glucose levels after stress. Stress-susceptible swine treated with phenoxybenzamine exhibited cutaneous red and white blotching, tail and ear tremors, forced deep and irregular respiration and physical collapse. They also had high plasma glucose levels, very high plasma lactate and a substantial blood pH decline after 5 min. of stress. Pigs treated with propranolol had lower levels of plasma lactate than pigs given phenoxybenzamine. Neither propranolol nor phenoxybenzamine significantly influenced plasma cortisol or growth hormone levels after the pigs were subjected to 5 min. of physical exercise. No significant treatment influences were observed on post-mortem muscle characteristics.

¹ Journal Paper No. J-7524 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 1697.

² The authors wish to express their appreciation to Dr. Gordon Thomson for his assistance on the statistical analysis, to Smith, Kline, and French Laboratories, Philadelphia, PA, for supplying the phenoxybenzamine and to Armour Food Research Division for partial support of this study.