Browsing by Subject "Estradiol -- Physiological effect"
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Item In vitro muscle cell protein synthesis and degradation, nitrogen balance and the feedlot response to trenbolone acetate, estradiol, and somatotropin in finishing beef steers(Texas Tech University, 1996-08) Thomson, Daniel UlanSteroidal implants have been used for 40 years to increase gain and gain efficiency of cattle by increasing protein deposition. However, the mechanism in which these hormones increase protein deposition is not fully understood. This dissertation is an in-depth study that utilized cell culture techniques to examine the indirect effects of serum from steers treated with steroid hormones and somatotropin on muscle cell proliferation and protein synthesis/degradation. Also, this dissertation studied the effect of steroid hormones on nitrogen balance, feedlot response and cellular composition of anterior pituitary cells in finishing steers. Treating steers with steroidal hormones alone and in combination with somatotropin increased the percentage of nitrogen retained relative to controls and steers given somatotropin alone. Both steroids and growth hormone depressed plasma urea nitrogen concentrations on days 1 and 4 of the collection period additively. Serum from steers given steroidal implants and growth hormone increased in vitro muscle cell proliferation and muscle cell protein synthesis, while having minimal effect on protein degradation. Directly administering steroids to cultured muscle cells had no effects on protein synthesis or degradation. Implanting steers with steroidal hormones increased average daily gain and gain efficiency and depressed plasma urea nitrogen relative to control cattle within the first 28 days following implantation. There was no consistent response to serum from these steers in muscle cell protein synthesis or degradation in vitro. Implanting steers 3 and 5 weeks prior to slaughter increased average daily gain while decreasing the marbling score in the carcasses. Implants did not cause dark cutting carcasses. Steroidal implants increased the percentage of somatotropes and decreased the percentage of mammosomatotropes in the anterior pituitaries of finishing beef steers. This dissertation concludes that steroid hormones do not have a direct effect on muscle cell protein deposition. Indirectly via factors in the serum, these hormones increase protein deposition by increasing protein synthesis. These steroid hormones given in combination with somatotropin increase protein synthesis and nitrogen retention. The mechanism for the increased protein deposition due to steroids may be the change in the percentage of acidophils in the anterior pituitary.Item The effects of estradiol and epidermal growth factor on the material properties of the skeletally immature rabbit anterior cruciate ligament(Texas Tech University, 2003-12) Cowden, CourtneyThere exists a troubling discrepancy between the number of anterior cruciate ligament (ACL) injuries between males and females. Indeed, the root causes of this difference are multifactorial in nature. One possible factor is the presence of female sex hormones in the ACL and their effects on collagen production. Also, cross-talk is known to exist between the estrogen receptor and epidermal growth factor (EGF) in reproductive tissues affecting collagen production. Twenty-four pre-pubescent New Zealand White rabbits were separated into three groups consisting of a control group receiving no hormones, a group receiving only estradiol, and a group receiving both estradiol and EGF. The rabbits were euthanized after the two-week period and had their hind limbs removed and frozen with soft tissue intact. All rabbit handling, hormone injections, and cataloging was performed by a separate laboratory creating a blind study environment. Before undergoing a standard tensile test, each ACL was analyzed using a 3D scanning technique capable of finding the minimal cross-sectional area and volume of the ligament. The test data was analyzed to assess significant differences in such values as the failure strength, strain at failure, modulus of elasticity, toughness, minimal cross-sectional area, length, and volume. Since all of the rabbits were pre-pubescent, no previous exposure to estradiol influenced the test results beyond the influence of the sex hormones which were administered. No differences were found between any groups for strain, length, minimal area, and volume. Estradiol was shown to lower the maximum stress by 39% while EGF in addition to estradiol had no effect on that property. EGF in combination with estradiol significantly lowered the modulus of elasticity while significance could not be proven for the effect of estradiol alone on the modulus. Toughness behaved similarly to maximum stress in its response to estradiol and EGF. Estradiol induced collagen degradation is a viable explanation for these differences in maximum stress and toughness. Further testing is necessary to establish a relationship between estradiol, EGF, and the modulus of elasticity.