Factors influencing testicular gonadotropin receptors and testis responsiveness to luteinizing hormone (LH) stimulation were studied during the seasonal sexual cycle of the adult ram. The normal variation in testis content of gonadotropin receptors was mapped out in relation to changes in (1) testis size, (2) testis responsiveness to LH stimulation and (3) mean serum concentration of LH, follicle stimulating hormone (FSH), testosterone and prolactin (PRL). The increase in gonadotropin receptor numbers during testicular redevelopment was preceded by elevated serum concentrations of PRL and associated with increases in both the frequency of endogenous pulses of LH and the responsiveness of the testis to LH stimulation. When serum PRL concentrations displayed abnormal variations in relation to photoperiod, the normal patterns of change in testis LH receptors and responsiveness to LH stimulation were altered. To determine if the increase in gonadotropin receptors was due to increased frequency of LH pulses up regulating homologous receptors, rams were injected, in the nonbreeding season with small, frequent doses of LH. Testis responsiveness was greatly enhanced but occurred independently of changes in gonadotropin receptor numbers or their binding affinities. To determine if the seasonal rise in serum PRL concentration was influencing gonadotropin receptors, endogenous secretion was suppressed by treatment with 2-bromo-X-ergocryptine (CB154) prior to and during testicular redevelopment. This resulted in delayed testicular redevelopment and reduced numbers of testicular LH receptors. Reduced numbers of LH receptors was associated with reduced responsiveness of the testis to LH stimulation. These results support the hypothesis that the seasonal increase in serum PRL concentration initiates testicular redevelopment by increasing LH receptors. Increases in LH peak frequency enhance responsiveness but this occurs independently of changes in gonadotropin receptors.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.72092 |
| Date | January 1987 |
| Creators | Baker, Susan Jane. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Animal Science.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 000547476, proquestno: AAINL44286, Theses scanned by UMI/ProQuest. |
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