The neuroendocrine sites and mechanisms of action whereby testosterone (T) regulates LH, FSH and prolactin signals in male rats were investigated by determining the effects of orchidectomy and graded T replacement on the secretion patterns of these hormones in blood. A chronic jugular catheter system was established to obtain blood samples at 5-10 min intervals from unrestrained, unanesthetized rats; this enabled moment to moment changes in plasma hormone concentrations, and thus hormone patterns, to be determined. In intact rats the patterns of LH and prolactin in plasma are pulsatile, but exhibit no synchrony; the FSH pattern shows no pulses. Post-orchidectomy LH concentrations rise due to increases in pulse amplitude and frequency; FSH also rises, but still no pulses are detected. Decreased prolactin pulse amplitudes result in lower plasma concentrations, despite an increase in pulse frequency. Treatment of orchidectomized rats with low doses of T increases mean LH and FSH concentrations, thus demonstrating that T is capable of exerting a positive feedback effect in males. The effect on LH is due to a stimulation of LH pulse amplitude which is not mediated at the pituitary. The FSH pattern becomes pulsatile and is synchronized with that of LH. Higher doses of T exert negative feedback on LH and FSH; LH pulse amplitude and frequency are decreased and the FSH pattern once again shows no pulses. These effects of T are partially due to inhibition of the pituitary response to LHRH. Low doses of T completely block the effects of orchidectomy on prolactin pulse amplitude, but T levels similar to those in intact animals are required to reverse the accelerated pulse frequency. The results suggest that gonadotropins and prolactin are regulated by separate pulse generators, each responsive to changes in plasma T. Furthermore, T, depending on its concentration, regulates gonadotropin and prolactin secretion by exerting stimulatory and/or inhibitory effects on various neur
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.75750 |
| Date | January 1987 |
| Creators | Grosser, Peter M. |
| 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 Pharmacology and Therapeutics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 000570079, proquestno: AAINL46101, Theses scanned by UMI/ProQuest. |
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