Please use this identifier to cite or link to this item: http://hdl.handle.net/10553/76956
Title: Effects of medroxyprogesterone acetate (MAP) on ovarian antral follicle development, gonadotropin secretion and response to GnRH in seasonally anovular ewes
Authors: Bartlewski, Pawel Mieczyslaw
Aravindakshan, J.
Beard, Andrew P.
Nelson, M. L.
Batista Arteaga, Miguel 
Cook, Susan J.
Rawlings, N. C.
UNESCO Clasification: 310907 Patología
Keywords: Medroxyprogesterone acetate
Gonadotrophin-releasing hormone
Ovulation
Anoestrus
Ewe
Issue Date: 2001
Journal: Biology of reproduction 
Abstract: When ovulation is induced with gonadotrophin-releasing hormone (GnRH) in anoestrous ewes, a proportion of animals fail to form normal (full-lifespan) corpora lutea (CL). Progesterone treatment before GnRH prevents luteal inadequacy. It remains uncertain whether a similar effect, achieved with medroxyprogesterone acetate (MAP) from intravaginal sponges, is mediated by influences on growing ovarian follicles and/or secretion of gonadotrophic hormones, before and after GnRH treatment. Two experiments were performed, on 13 and 11 anoestrous Western white-faced ewes, respectively. Seven and six ewes, respectively, received MAP-containing sponges (60 mg) for 14 days; the remaining ewes served as untreated controls. To test the effect of timing of GnRH administration after pre-treatment with MAP-releasing sponges, GnRH injections (250 ng every 2 h for 24 h followed by a bolus injection of 125 μg of GnRH i.v.) were given either immediately (Experiment 1) or 24 h after sponge removal in the treated ewes (Experiment 2). Ovarian follicular dynamics (follicles reaching ≥5 mm in size) and development of luteal structures were monitored using transrectal ultrasonography. In Experiment 1, the mean ovulation rate (0.7±0.3 and 1.0±0.4) and proportion of ovulating ewes (57 and 67%, respectively) did not vary (P>0.05) between MAP-treated and control ewes. Normal (full-lifespan) CL were detected in 29% of treated and 67% of control ewes (P>0.05). In Experiment 2, the mean ovulation rate (2.3±0.2 and 1.2±0.6; P<0.05) and percentage of ewes with normal (full-lifespan) CL (100 and 40%, respectively; P<0.10) were greater in the treated compared to control ewes. In Experiment 1, the mean peak concentration of the GnRH-induced LH surge was lower (P<0.05) in MAP-treated than in control ewes. There were no significant differences between MAP-treated and control ewes in the characteristics of follicular waves, mean daily serum FSH concentrations, and secretory parameters of LH/FSH, based on intensive blood sampling conducted 1 day before sponging and 1 day before sponge removal. It is concluded that treatment with MAP has no effect on the tonic secretion of LH/FSH or follicular wave development in anoestrous ewes. However, the GnRH-stimulated LH discharge was attenuated in the ewes that received MAP-impregnated sponges for 14 days and were treated with GnRH immediately after sponge withdrawal. Ovulatory response and CL formation were increased when GnRH was administered 24 h after sponge removal.
URI: http://hdl.handle.net/10553/76956
ISSN: 0006-3363
Source: Biology of reproduction [ISSN 0006-3363], v. 64 (sup. 1), p. 150, (2001)
Appears in Collections:Actas de congresos
Show full item record

Page view(s)

16
checked on Jul 31, 2021

Google ScholarTM

Check


Share



Export metadata



Items in accedaCRIS are protected by copyright, with all rights reserved, unless otherwise indicated.