The Role of Gonadotropic Hormones in Follicular Maturation of the Domestic Hen
Ritzhaupt, Larry Keith
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https://hdl.handle.net/2142/70054
Description
Title
The Role of Gonadotropic Hormones in Follicular Maturation of the Domestic Hen
Author(s)
Ritzhaupt, Larry Keith
Issue Date
1987
Doctoral Committee Chair(s)
Bahr, Janice M.
Department of Study
Animal Sciences
Discipline
Animal Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Abstract
The theme of this thesis is the role of gonadotropins in regulating follicular development and ovulation in the domestic hen, Gallus domesticus. These investigations focused on a role for methylation in the regulation of adenlyly cyclase (AC) activity and progesterone (P) secretion in granulosa cells as well as the role of follicle-stimulating hormone (FSH) receptors on granulosa cells during follicular maturation.
Two studies on methylation were conducted. In the first study, granulosa cells were incubated with various combinations of luteinizing hormone (LH), a methyl donor, and an inhibitor of methylation. Following incubation basal and LH-stimulable AC activity were measured. In the second part of the study, granulosa cells were incubated and P secretion measured following treatment with various combinations of LH, a methyl donor, and inhibitors of methylation. In both studies, neither the methyl donor nor the inhibitors of methylation affected basal responses. However, the methyl donor in the presence of the LH decreased both AC activity and P production. These responses were blocked by a methylation inhibitor. These results suggest that the effect of methylation was at the level of the membrane. I hypothesize that the stimulatory hormone activates methyltransferase enzymes in the membranes which change the phospholipid content of the membrane and cause a suppression of the hormone-stimulated response. The physiological significance of this suppression by methylation may be as a regulator of the follicular hierarchy in the hen.
An FSH receptor assay was validated to investigate the role of FSH receptors during follicular maturation. Following validation of the assay, equilibrium binding studies were performed and the numbers of FSH receptors present and the affinity of the receptors for radiolabelled FSH were measured in small, medium, and large follicles. The affinity of the FSH receptors did not change as follicles increased in size and approached ovulation. The numbers of FSH receptors decreased as the follicles increased in size. The decrease in the number of the FSH receptors is correlated with the reported decrease in FSH-stimulable AC activity and steroidogenesis. It is concluded that the decrease in FSH responsiveness in granulosa cells during follicular maturation is regulated by the number of FSH receptors.
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