|Walker, M - TEXAS A&M UNIVERSITY|
|Hartsfield, S - TEXAS A&M UNIVERSITY|
|Green, N - TEXAS A&M UNIVERSITY|
|Mcarthur, N - TEXAS A&M UNIVERSITY|
|Welsh, JR., T - TEXAS A&M UNIVERSITY|
Submitted to: Laboratory Animals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 21, 2006
Publication Date: March 15, 2007
Citation: Carroll, J.A., Walker, M.A., Hartsfield, S.M., McArthur, N.H., Welsh, Jr., T.H. 2007. Visual documentation on ovine pituitary gland development with magnetic resonance imaging following zeranol treatment. Laboratory Animals. 41:120-127. Interpretive Summary: Animal biologists and livestock producers are interested in the control of growth and development in young animals. As rate of gain and feed efficiency affect the success of food production systems, many food animal specialists utilize exogenous hormonal therapy (i.e., androgenic and estrogenic anabolic agents) to increase growth performance of ruminant livestock. The ability of these exogenous steroidal agents to affect synthesis and secretion of growth hormone by the pituitary gland is of specific practical and clinical relevance. Endocrinologists rely on tissues and glands collected post-mortem to address pertinent questions about the endocrine system components while clinicians often use endocrine testing to confirm a diagnosis. These useful methods have limits regarding the study of the ontogeny of endocrine gland development for any one animal. Thus, new technologies have been sought to identify specific periods during which endocrine gland development and perhaps cellular function could be evaluated. Fortunately, the opportunity to monitor the growth and development of endocrine glands in vivo without testing or sacrificing the animal has become possible with the advent of magnetic resonance imaging (MRI) technology. Therefore, the primary objective was to determine whether MRI could be utilized to visually document (over time and within the same animal) the effect of zeranol (an estrogenic anabolic agent) on growth and development of the pituitary gland in wethers. The results demonstrated that: 1) MRI can reveal an increase in area of the pituitary gland, as visualized in three anatomic planes (i.e., sagittal, transverse and dorsal); 2) calculations based on the MRI measurements can be used to quantitate an increase in the volume of the pituitary gland; and 3) MRI can provide visual evidence of alterations in pituitary gland size induced by an estrogenic anabolic agent. Also, this study showed the importance of obtaining images from at least two of the three anatomic planes for precise representation of the growth of the pituitary gland in vivo. The findings from this study utilizing MRI, coupled with other endocrine physiology procedures, will facilitate identification of whether, when, and how peptide, non-peptide, and steroidal anabolic agents increase the synthesis and secretion of growth hormone. Technologies such as MRI which allow visual documentation of in vivo pituitary gland growth, as well as growth, development, and function of other intracranial structures (i.e., thalamus, hypothalamus, pineal gland, etc) will undoubtedly enhance not only diagnostic procedures used for humans and animals, but will provide a novel approach for endocrinologists and physiologists to identify and understand the growth, development, and function of endocrine glands over time and within the same animal.
Technical Abstract: The objective of the current study was to determine whether Magnetic Resonance Imaging (MRI) could be successfully utilized to document the effect of an estrogenic anabolic agent on pituitary gland growth. The experimental animals consisted of two 1/2-sibling Suffolk wethers which received either no implant (control, n=1) or a 24-mg zeranol implant at week 0 and 6 (zeranol; n=1). Animals were anesthetized with propofol and supported with oxygen during the MRI procedure. A mobile MRI unit with a 0.5 tesla (T), superconducting magnet was used to obtain 3-mm thick, non-contrast enhanced, T1 weighted (TR 500-600, TE25) sagittal, transverse, and dorsal images of the pituitary gland. Sagittal images were recorded only when the mesencephalic aqueduct and infundibulum were distinctly visible in the same image. Pituitary glands were imaged at 2-wk intervals for 10 wk to determine if and when the anabolic effects of zeranol on pituitary gland growth could be visualized using MRI techniques. Three separate measurements of the pituitary gland dimensions made with the on-screen cursor were averaged to calculate pituitary gland dimensions and volume. A computer assisted image analysis system and laser film images were used to determine pituitary gland area. Pituitary gland volume (Week 0 vs Week 10) increased by 50 and 150% for the control and zeranol-treated wethers, respectively. The differences in percent increase in pituitary gland volume were apparent by 2 wk post-implantion [Week 2 (control=11% vs zeranol=55%); Week 8 (control=2% vs zeranol=48%)]. Overall, our results indicate that MRI technology can be successfully used to document the development of the pituitary gland in vivo. Application of knowledge gained from this novel approach to study the growth, development, and function of endocrine glands over time and within the same animal, will enhance human and animal endocrine diagnostic procedures.