Author
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Mersmann, Harry |
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Submitted to: Journal of Animal Science
Publication Type: Abstract Only Publication Acceptance Date: 5/1/1997 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: The Beta-adrenergic receptors (Beta-AR) are present on the surface of almost every type of mammalian cell. These receptors are stimulated physiologically by the neurotransmitter, norepinephrine, and the adrenal medullary hormone, epinephrine. There are three subtypes of Beta-AR, namely Beta1-AR, Beta2-AR, and Beta3-AR; the pharmacological and physiological responses of an individual cell result from the particular mixture of the three Beta-AR subtypes present in that cell. Species-specific structure (amino acid sequence) also causes modification of the function of a given Beta-AR subtype. Knowledge of the Beta-AR subtypes present in various cell types, coupled with knowledge of receptor structure (sequence), will allow an understanding of the complexity of physiological function regulated by Beta-AR. Oral administration of some Beta-AR agonists increases muscle and decreases fat accretion in cattle, pigs, and sheep. The large number of physiological functions controlled by Beta-AR suggests the mechanism(s) fo the observed changes in carcass composition may be extremely complex. Any proposed mechanism must begin with the possibility of direct effects of the agonist on skeletal muscle and adipocyte Beta-AR. However, many other mechanisms, such as modification of blood flow, release of hormones, or central nervous system control of feed intake may contribute to the overall effects observed with a given Beta-AR agonist in a given species. Further- more, the pharmacodynamic properties of a particular agonist are complex and expected to be different in different species as well as in the same species at different ages or when fed different diets. |
