Date of Award

Spring 1997

Project Type

Dissertation

Program or Major

Animal and Nutritional Sciences

Degree Name

Doctor of Philosophy

First Advisor

Joanne Corran-Celentano

Abstract

There have been conflicting reports which associate a low dietary intake or plasma concentration of beta-carotene (BC) with decreased fertility in dairy cows. The bovine corpus luteum (CL), a transient endocrine gland formed subsequent to ovulation, produces the steroid hormone progesterone which sustains pregnancy and is associated with fertility. Because of its high concentrations of the antioxidant nutrient beta-carotene, the CL was examined to identify an in vivo function for BC, other than that as a precursor of retinol. Five non-lactating Jersey cows were fed a basal ration containing a low BC concentration. Each cow received either 0, 1.6, 8.0, 16.0, or 80.0 mg/day of supplemental BC in the form of water-soluble beadlets incorporated into grain. Changes in plasma BC were measured weekly. After each of four feeding periods (7 weeks each), a mid-cycle CL (9-11 days following estrus) and plasma were harvested from each cow. Plasma and CL beta-carotene concentrations were directly related to the dietary BC level and, while on the BC deficient diet were similar to those seen in humans. Western immunoblotting was used to identify, the steroidogenic enzymes adrenodoxin (Adx, $\sim$14 kDa) and cholesterol side-chain cleavage cytochrome P-450 (P450scc, 49 kDa). The enzymes Adx and P-450scc catalyze the first and rate-limiting reaction in progesterone synthesis. Antisera specific for Adx or P450scc, in addition to recognizing their respective proteins, recognized a protein of higher molecular weight (63 kDa). The 63 kDa protein band, believed to be P450scc and Adx chemically cross-linked in a one to one ratio, was present consistently in the lanes where CL beta-carotene concentrations were below $\sim$11 nmol/g. On the other hand, the cross-linked protein was not apparent in lanes where the CL beta-carotene concentrations were above $\sim$50 nmol/g. In lanes where the CL beta-carotene concentrations were between 11 and 50 nmol/g, the cross-linked protein was sometimes apparent, but not consistently. Thus, it appears that BC protects the mitochondrial enzymes Adx and P450scc against damage from free radicals produced during steroidogenesis. These observations may help explain studies which show that antioxidant vitamins enhance steroid production.

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