Somatotroph differentiation during chicken embryonic and post-hatch development /
In the chicken, somatotrophs first appear occasionally on day
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1996.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=743266971&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | In the chicken, somatotrophs first appear occasionally on day 12 and become a significant population on day 16 of embryonic development. We have previously demonstrated that somatotroph differentiation can be induced in cultured day 12 pituitary cells by serum derived from day 16 embryos. The first part of the research presented here was designed to identify the blood-bome signal, and to test the ability to stimulate somatotroph differentiation in vitro. Biochemical analysis revealed an ethersoluble, heat-resistant compound, inhibited by a trypsin-sensitive protein. As such, several steroids were tested for their ability to stimulate differentiation. Corticosterone, progesterone and 170- estradiol were capable of stimulating differentiation. The estradiol receptor antagonist Tamoxifen abolished the stimulatory effect of the steroid, without altering the effect of day 16 serum. The glucocorticoid receptor antagonist RU486 not only abolished the stimulatory effect of corticosterone and progesterone, it also successfully blocked the effect of day 16 serum. Incubation of day 16 serum with corticosterone antibody, but not with progesterone antibody, abolished the stimulatory effect of the serum. Therefore, we conclude that the blood-bome factor responsible for somatotroph differentiation in vitro is a glucocorticoid. Next, in order to gain a better understanding of somatotroph differentiation in vivo, day 1 1 eggs were injected with day 12 and day 16 serum. By day 14, assays revealed that day 16, but not day 12 serum, stimulated somatotroph differentiation in ovo, which was successfully mimicked with corticosterone. Corticosterone stimulated somatotroph differentiation in ovo in a dose-related manner, both directly and indirectly following activation of the hypothalamo-pituitary-adrenal axis, with corticotropin releasing factor (CRF) and adrenocorticotropic hormone (ACTH). The normal process of somatotroph differentiation was blocked by day 16 after 4 daily injections of RU486. Therefore, we conclude that corticosterone stimulation is required for normal somatotroph differentiation during chicken embryonic development. In the last chapter, the cellular basis for gender-dependent growth hormone (GH) secretion in rapidly-growing chickens was studied. Males were found to have a higher percentage of somatotrophs, and somatotrophs from males released more hormone in response to GH- releasing hormone. |
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| Item Description: | Vita. "Major Subject: Poultry Science". |
| Physical Description: | xii, 115 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |