Thesis (M. Phil.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 89-106).

Thesis (M. Phil.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 68-84).

published_or_final_version / abstract / Biological Sciences / Doctoral / Doctor of Philosophy

M.Sc. / This study aims to assess the potential impacts of intense feedlot activity on the aquatic freshwater environment, with reference to three feedlots, ranging in production size and all situated in the upper Vaal catchment area. Field assessments were done over a high flow and low flow period, while controlled exposures were also done to quantify a potential stress reaction to growth hormone exposure (using Clarias gariepinus as test organism). It was ascertained that water quality variables contributing towards differences between upstream and downstream environmental conditions are NH4 concentrations pH and conductivity. Lead concentrations were also periodically higher downstream from feedlot activity, in comparison with upstream. Taking the sediment assimilation potential of growth hormones into consideration, it was determined that Feedlot C showed the highest assimilation potential, while Feedlot A reflected the lowest. Alterations on family level invertebrate community structures indicated a categorical decline in abundances and species richness at sites situated downstream from feedlots. However, some clear seasonal influences were also observed. Further community and diversity analyses reflected alterations in invertebrate community structures that were not reflected in SASS 5 scores. With regards to the biomarkers applied in this study, it was noted that there was a significant (p<0.05) difference in the cellular energy allocation (CEA) between control and hormone exposed groups. The total amount of energy available (Ea) increased significantly for test organisms exposed to Diethylstilbestrol (DES), while there was a significant increase in energy consumption (Ec) of test organisms exposed to Trenbolone acetate (TBA). In addition to CEA, metabolic profiling of blood plasma was also performed, which indicated a definite ordination in metabolic constituents after fifteen days of exposure. This was established by subjecting the data to principle component analysis (PCA), which accounted for 83 % variance observed. The impacts and biotic responses identified in this study were contextualised with known literature on the effects of feedlot activity and growth hormone exposure on the aquatic environment. Finally, conclusions were drawn and recommendations made with regard to improving feedlot operational activities. The results obtained in this study contribute towards an integrated framework for the environmental management of feedlot activities.

No description available.

Growth hormone-releasing hormone (GRF) and pituitary adenylate cyclase-activating polypeptide (PACAP) are members of the PACAP/Glucagon superfamily. The family is proposed to have developed from an ancestral PACAP-like molecule in invertebrates. Through successive exon, gene and genome duplications the family has grown to include seven other members. In mammals GRF and PACAP are located on different genes, but in fish, amphibians and birds they are located on the same gene. The main function of GRF is the release of growth hormone (GH) from the pituitary. Also, during development GRF influences the fetal pituitary and stimulates GH release during late gestation. In contrast, the functions of PACAP are extremely varied. PACAP is the newest member of the superfamily and there is still much work to be done before its actions are well understood. Like GRF, PACAP is a releasing hormone acting on the pituitary and in addition, the adrenal gland, pancreas and heart, as well as other organs. Also, PACAP regulates smooth muscle in the vascular system, gut, respiratory tract and reproductive tract During development PACAP affects proliferation, differentiation and apoptosis. GRF and PACAP are expressed throughout development in fish, beginning during the blastula period in rainbow trout and at the end of gastrulation in zebrafish (earliest stage examined). In rainbow trout the grf/pacap gene is expressed as two transcripts, a short and a long transcript. The short transcript is produced by alternative splicing of the gene and does not include the fourth exon which codes for GRF. The long transcript includes the coding regions for both GRF and PACAP. By this means PACAP can be regulated separately from GRF. With the extensive role PACAP appears to play in development, separate regulation of the hormone may be necessary. Expression of the grf/pacap gene in zebrafish is widespread early in development and gradually becomes localized. Of particular interest is the expression of the grf/pacap transcript in regions associated with the prechordal plate, an important organizing center in development. Although it is not yet confirmed, there is evidence to suggest GRF and PACAP are expressed in the prechordal plate and its derivatives in the gut and hatching gland. In addition, expression of the grf/pacap transcript is observed in the neuroectoderm (eye, brain and spinal cord) and the developing heart. Considering the expression pattern of GRF and PACAP, I propose that one of both of these hormones may be involved in patterning during vertebrate embryogenesis. The evolution of gene families is thought to occur through successive exon, gene and genome duplications. Duplicate exons or genes become differentiated and eventually gain new functions or become functionless. During evolution of the grf/pacap lineage, several duplication events have occurred. Analysis of rainbow trout leads me to think that this fish and other salmonids possess two copies of the grf/pacap gene. This is not unexpected considering the tetraploid nature of salmonids. Present day mammals encode GRF and PACAP on separate genes. At some point during the evolution of this lineage a duplication event has occurred, possibly in early mammals or prior to the divergence of birds. The study of multigene families is a useful way to understand evolutionary processes. To this end I examined three members of multigene families from sockeye salmon. Therefore, in addition to the evolutionary mechanisms and pathways that directed grf/pacap gene evolution, I examined the ferritin-H subunit, the alpha-tubulin subunit and the beta-globin subunit. These cDNA sequences are similar to their counterparts in other teleost. The evolution of the ferritin gene family is particularly interesting because it involves the addition or deletion of DNA sequences that affect regulation and cytosolic location. / Graduate

In a HEK 293 cell line stably expressing seabream GHS-R1a (sbGHS-R1a), we found that a synthetic growth hormone secretagogue (GHS) increased [ 3H]-inositol phosphate production, clearly indicating coupling of this receptor to Gq/11-proteins. Using Western blotting, we found that GHS could also stimulate extracellular signal-regulated kinases 1 and 2 (ERK1/2), and that this response was inhibited by the MEK inhibitor U0126. For both the [3H]-inositol phosphate and ERK1/2 assays, the presence of the GHS-R antagonist D-Lys(3)-GHRP-6 significantly inhibited the GHS-stimulated activities, and in addition inhibited basal activities by 50% and 40%, respectively. These results showed that sbGHS-R1a is a constitutively active receptor and the antagonist D-Lys(3)-GHRP-6 is an inverse agonist. We also proposed that the expression of sbGHS-Rs was involved in the regulation of cell apoptosis. / Oligomerization of the human GHS-Rs (hGHS-Rs) was explored by transient transfection of the hGHS-Rs in HEK 293 cells followed by co-immunoprecipitation of differentially epitope-tagged forms of the receptors and bioluminescence resonance energy transfer 2 (BRET2) studies. (Abstract shortened by UMI.) / The concept that G protein-coupled receptors (GPCRs) exist and potentially function as dimers and/or higher oligomers has progressed from hypothesis to being widely accepted recently. Oligomerization of GPCRs has been increasingly noted in the regulation of the biological activity of the receptors. The growth hormone secretagogue receptor 1a (GHS-R1a) is a GPCR which principally regulates the pulsatile release of growth hormone from the pituitary gland. The GHS-R exists in two forms: GHS-R1a being a constitutively-active GPCR with 7 transmembrane (TM) domains, and GHS-R1b being a truncated version of type 1a but having only 5 TM domains. The endogenous agonist for GHS-R1a is ghrelin which exerts a wide range of physiological actions, but the function of GHS-R1b is still unclear. Since the tissue distribution patterns of the two isoforms of GHS-R are different, the objective of the present study is to explore the mechanisms of cell signalling of GHS-R1a and to determine the extent and importance of interactions between these two receptor isoforms. / Leung Po Ki. / "July 2005." / Adviser: Helen Wise. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3728. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 189-210). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / School code: 1307.