An alternative approach to premature luteal regression

Pretorius, Willem S (Stellenbosch : Stellenbosch University, 2006-12)

Thesis (MSc)--University of Stellenbosch, 2006.

Thesis

ENGLISH ABSTRACT: Premature luteal regression occurs on average in 30% of superovulated sheep ewes. This phenomenon occurs early in the cycle before the embryo’s can be collected and is a major contributor to failure in embryo transfer programs. This research was done to understand the physiological mechanisms involved. Chapter two provides a general background of the physiology of natural luteolysis and the maternal recognition of pregnancy. The chapter introduces some new concepts on the topic of cell death and provides a recent literature review on research done on the phenomenon of premature luteal regression. This chapter forms the base of ideas and arguments that follows in the two studies containing new original work in this field. The research contained in this thesis comprises of two in vivo studies. The first study (Chapter 3) compare premature luteal regression to Prostaglandin F2α (PGF2α) induced regression with emphasis on the changes in levels of the steroid hormones progesterone (P4) and estradiol - 17β (E2-17β) and changes in structure and ultra structure. The following conclusions were made: 1. Premature luteal regression is not merely inadequate luteal support, but indeed early luteal regression, since seasonal influences could merely be nutritional influences, and a definitive increase in P4 were recorded in animals exhibiting the phenomena. 2. Nutritional influences could play a role, but the type and quality of nutrients and mechanism involved, is still unclear. 3. PGF2α-induced regression differs from premature luteal regression in that: a) The progression of functional and structural regression in PGF2α -induced regression is slower than in premature luteal regression. b) Regressed corpora lutea do not occur with normal functioning corpora lutea. 4. There is a distinct second E2-17β peak preceding the decline in P4 in animals that exhibits signs of premature luteal regression. A threshold initiating premature luteal regression was not established. The second study (Chapter 4) compares the changes in the ovine β estradiol - 17 β receptor (oERβ) between premature luteal regression and PGF2α induced regression. The study concludes that there could be a potential role for oERβ in premature luteal regression. The findings of these two studies raise some questions about the conventional perception that early release of PGF2α is the cause of premature luteal regression. The thesis concludes in a hypothesis (Chapter 4) explaining the phenomenon.

AFRIKAANSE OPSOMMING: Premature luteale regressie kom gemiddeld in 30% van gesuperovuleerde skaap-ooie voor. Die verskynsel kom vroeg in die siklus voor, voor die embrios gekollekteer kan word, en is een van die belangrikste oorsaake van mislukkings in ‘n embrio-oorplaasingsprogram. Die huidige navorsing poog om die fisiologiese meganismes betrokke by premature luteale regressie te verstaan. Hoofstuk twee verskaf ‘n algemene agtergrond van die fisiologiese aspekte betrokke by natuurlike luteale regressie en maternale herkenning van swangerskap. Die hoofstuk stel nuwe konsepte voor oor sel afsterwing en verskaf ‘n opgedateerde literatuuroorsig met betrekking tot die navorsing wat in die veld oor die verskynsel gedoen is. Die hoofstuk vorm die basis vir die idees en argumente, wat volg in die twee studies en wat oorspronklike nuwe navorsing bevat oor die onderwerp. Die navorsing in die tesis bestaan uit twee in vivo studies. Die eerste studie (Hoofstuk 3) vergelyk premature luteale regressie en prostaglandien F2α (PGF2α) ge-induseerde regressie met ‘n klem op die vlakke van die steröiedhormone progesteroon (P4) en estradiol - 17β (E2-17β) en veranderinge in die mikroskopiese struktuur en ultra struktuur van die corpus luteum. Die studie bevind: 1. Premature luteale regressie is nie slegs onvoldoende luteale funksie nie, maar vroë luteale regressie aangesien seisoenale invloede eitlik voedings invloede kan wees en P4 gestyg het in diere waar die verskynsel voorgekom het. 2. Voeding kan ‘n rol speel maar die tiepe en gehalte van die voedingstowwe en die meganismes betrokke is nie duidelik nie. 3. PGF2α - ge-induseerde regressie verskil van premature regressie in dat: a) Die verloop van funksionele en strukturele regressie is stadiger in PGF2α - ge-induseerde regressie in vergelyking met premature luteale regressie. b) Corpora lutea wat regressie ondergaan het kom nie voor saam met corpora lutea wat normal voorkom nie. 4. Daar die ‘n duidelike tweede piek van E2-17β gaan die afname in P4 vooraf in diere waar premature regressie voorkom. 5. Daar is nie geslaag om ‘n drempel vas te stel waar premature regressie ge-inisieer word nie. Die tweede studie vergelyk die veranderinge in estradiol-17β reseptore (oERβ) in die skaap tydens premature luteale regressie en PGF2α geinduseerde regressie. Die studie bevind dat daar ‘n moontlike rol is vir ERβ in premature luteale regressie. Die bevindinge van die twee studies bevraagteken die konvensionele opvatting dat vroë vrystelling van PGF2α verantwoordelik is vir premature luteale regressie. Die tesis sluit af met ‘n nuwe hipotese om die verskynsel te verduidelik.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/17406
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