Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Science

First Advisor

Allen Trenkle


While the importance of endocrine regulation of growth is well known, it is less clear how the endocrine hormones interact to regulate skeletal muscle growth. The objective of these studies was to determine the effects growth hormone (GH), estradiol 17-[beta] (E[subscript]2), thyroid hormones, and insulin-like growth factor-1 (IGF-1), exert on muscle growth and IGF-1 messenger ribonucleic acid (mRNA) concentrations in liver and skeletal muscle of growing cattle. IGF-1 mRNA concentrations in liver and skeletal muscle samples obtained either at slaughter or by biopsy, were measured using solution hybridization;In the first experiment, cattle with normal physiological differences of plasma GH (bulls, steers, heifers), liver IGF-1 mRNA concentrations were significantly correlated to plasma GH peak amplitude concentrations while skeletal muscle IGF-1 mRNA concentrations were unaffected by GH. Thyroid status seemed to be negatively related to muscle IGF-1 mRNA expression;In the second experiment, daily administration of exogenous GH (150 ug/kg body weight) to steers significantly increased liver IGF-1 mRNA and plasma IGF-1 concentrations, but had no effect on IGF-1 mRNA concentrations in skeletal muscle. Implanting steers with E[subscript]2 (approximate release, 60 ug/day) significantly increased mean plasma GH concentrations, peak amplitudes of plasma GH concentrations, and liver and skeletal muscle IGF-1 mRNA concentrations. E[subscript]2 depressed the stimulation of liver IGF-1 mRNA concentrations by exogenous GH;In the third experiment, decreasing thyroid activity by oral administration of thiouracil (25 g/day) or increasing thyroid activity by injecting scL-thyroxine 0.6 ug/kg body weight), did not alter liver or skeletal muscle IGF-1 mRNA concentrations, plasma GH profile parameters, or plasma IGF-1 concentrations;The results of these studies suggest that in relationship to skeletal muscle growth in cattle, GH magnifies the importance of endocrine acting IGF-1, stimulating liver IGF-1 synthesis and plasma IGF-1 concentrations, while E[subscript]2 stimulates the autocrine/paracrine actions of IGF-1, directly stimulating skeletal muscle production of IGF-1.



Digital Repository @ Iowa State University,

Copyright Owner

Kevin Mark Hannon



Proquest ID


File Format


File Size

119 pages