Semester

Fall

Date of Graduation

2005

Document Type

Dissertation

Degree Type

PhD

College

School of Medicine

Department

Physiology, Pharmacology & Neuroscience

Committee Chair

Jorge A. Flores.

Abstract

The corpus luteum (CL) is a transient endocrine gland that produces progesterone (P4) for the establishment and maintenance of pregnancy. In absence of pregnancy, timely regression of the CL is essential for normal ovarian cyclicity. Several factors are known to participate in luteal regression. In this study, two factors, PGF2 alpha and endothelin (ET-1) are being studied. Protein kinase C (PKC) and calcium are the two main intracellular mediators of PGF2 alpha. The role of ET-1 in the regulation of luteal regression is unclear. The early CL is insensitive to the luteolytic actions of PGF2 alpha and the cellular mechanism(s) involved in this process are poorly understood. This study investigates: (1) the array of PKC isozyme expression as a function of development in the bovine CL and the ability of PGF2 alpha and ET-1 to activate the PKC isozymes in the early (day-4) and late (day-10) luteal phase, (2) the physiological role of the luteal PKC isozymes on PGF2 alpha-induced rise in intracellular calcium concentration and luteinizing hormone (LH) stimulated P4 accumulation at the mid luteal phase and (3) the cellular source of the luteal PKC isozymes. PKC alpha, beta I, beta II, epsilon and meu were observed to be expressed in the bovine CL with beta II and epsilon being differentially expressed as a function of development. In day-10 CL PGF2 alpha and ET-1 were able to activate PKC alpha, beta I and epsilon. More importantly, PKC epsilon was found to be involved in the regulation of PGF2 alpha induced rise in intracellular calcium concentration and antagonized the inhibitory effect of PGF2 alpha and ET-1 on LH-stimulated P4 accumulation in cultures of day-10 luteal steroidogenic cells (SC). PKC epsilon was found exclusively expressed in SC. In contrast, PKC alpha, beta I and beta II were expressed in both SC and endothelial cells (EC), with SC expressing higher amounts than EC. In this study we have proposed that the differential expression and activation of PKC epsilon as a function of development may be one of several factors responsible for the insensitivity of the early CL. Expression of PKC epsilon in the mid luteal phase shifts the PGF2 alpha induced rise in intracellular calcium concentration from a P4 favorable to a P4 inhibitory condition. Based on these observations it is hypothesized that the insensitivity of the early CL towards the luteolytic actions of PGF2 alpha may be due to differences in the intracellular mediators with respect to luteal development.

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