| Abstract No.: | A-E1171 |
| Country: | Canada |
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| Title: | PROLONGED LACTATIONAL INFERTILITY IN FOOD RESTRICTED LACTATING RATS:
ROLES FOR BOTH THE NPY Y5 RECEPTOR AND PROGESTERONE RECEPTOR |
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| Authors/Affiliations: | 1 Nicole Bellefontaine*; 1 Sharon Ladyman; 1 Barbara Woodside;
1 Concordia University, Montreal, QC, Canada
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| Content: | OBJECTIVES: In many species lactation is accompanied by a period of anovulation which in ad libitum fed rats nursing 8 pups lasts for approximately 21 days. Food restricting lactating rats on days 1-14 postpartum, prolongs this period by 7 days. Progesterone (P) is a major source of the negative feedback on hypothalamic neurons controlling the reproductive axis during lactation and circulating P levels are higher in food restricted (FR) than in ad libitum (AL) fed lactating rats. There is also converging evidence to suggest that the neuropeptide Y (NPY) Y5 receptor subtype, which is up regulated during lactation, also provides a source of negative feedback onto GnRH neurons. The objective of the current study was to investigate the role of the NPY Y5 receptor alone or in combination with a progesterone receptor blocker in the prolongation of lactational infertility by food restriction.
METHODS AND MATERIALS: Production of the Y5 receptor was blocked via chronic infusions of antisense oligodeoxynucleotides (ODNs) targeted to the Y5 receptor into the 3rd ventricle from day 13 to day 19 postpartum, inclusive. Control treatments for FR dams included equivalent scrambled ODNs or a vehicle treatment. Vehicle infused AL fed dams served as an additional control. Half of each treatment group received injections of RU486 (5mg/kg), a P receptor blocker, from day 15 to day 18 postpartum, inclusive. Dam and pup weight were recorded from day 1 postpartum, and termination of lactational infertility was determined by examining vaginal cytology from day 4 postpartum onwards.
RESULTS: The length of lactational diestrous was significantly longer for FR dams treated with vehicle than for any other group. Length of lactational infertility was similar in AL fed dams and FR dams treated with the either RU486 or Y5 antisense ODNs. FR dams treated with both Y5 antisense ODNs and RU486 injections had a shorter period of lactational infertility than any other group including AL-fed females.
CONCLUSIONS: These results show that reducing either progesterone receptor or Y5 receptor signalling is equally effective in shortening the length of lactational infertility in FR dams and this effect is increased when the two treatments are combined. Precisely how these two signals produce their effects remains to be determined. In current studies we are assessing the effects of these treatments on pulsatile luteinizing hormone release.
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