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Sexual dimorphism in prolactin secretory patterns and their regulation by estradiol in adult sheep

We investigated possible sex differences in PRL secretory patterns and regulation by E$ sb2$ in gonadectomized Dorset x Leicester x Suffolk sheep kept under natural photoperiod (latitude 45$ sp circ 31 sp prime$). Patterns were assessed over 14 months in groups of 10 rams and ewes, half of which received E$ sb2$ replacement (Silastic implants) at the time of gonadectomy to maintain blood E$ sb2$ at ram breeding-season values. Mean monthly PRL level (based on two 3-h periods of blood sampling) was consistently elevated by E$ sb2$ in the ram (mean 19%), and during all but a few months in the spring and summer in the ewes (mean 90%). Sex differences in the mean PRL were most apparent for the E$ sb2$-treated sheep in August (rams 280 $ pm$ 54 ng/ml vs ewes 128 $ pm$ 18 ng/ml) and for the control sheep in November (rams 19 $ pm$ 5 ng/ml vs ewes 10 $ pm$ 2 ng/ml). Episodic PRL secretion (with 5-min sampling for 4 h) was assessed in every season. In all four groups, pulse amplitude and frequency and basal level were higher in summer than winter. E$ sb2$ treatment was associated with larger PRL pulses in both sexes in every season but summer, and with decreased (from 8.2 to 4.6 per 4 h) and increased (from 2.2 to 6.6 per 4 h) frequencies of pulses in rams in the spring and summer, respectively. The PRL response to TRH (two iv injections 50 ng/kg BW given 80 min apart) was also assessed in every season. Mean 40-min increases after injection were highest in spring and summer. E$ sb2$ treatment produced in both sexes a 2-3 fold larger increment 1 in every season, and increment 2 in specific seasons. Preinjection and increment values were positively correlated within animals of each group across seasons (r = 0.89 and 0.65). The Incr 2/lncr 1 ratio (mean 0.76 $ pm$ 0.10) was not affected by seasons or E$ sb2$, and did not denote a self priming effect of TRH. Diurnal patterns indicated that PRL mean levels during light and dark phases were not different from each other within

Identiferoai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.69523
Date January 1993
CreatorsPaquette, Julie
ContributorsSanford, L. M. (advisor)
PublisherMcGill University
Source SetsLibrary and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada
LanguageEnglish
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation
Formatapplication/pdf
CoverageMaster of Science (Department of Animal Science.)
RightsAll items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated.
Relationalephsysno: 001338404, proquestno: AAIMM87817, Theses scanned by UMI/ProQuest.

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