Semester

Summer

Date of Graduation

2007

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

Matthew E. Wilson.

Abstract

The current experiments were conducted to determine if insulin could alter the progesterone catabolic enzymes, cytochrome P450 2C and 3A in vitro, utilizing a mouse hepatocyte cell-line, or in vivo, utilizing the ovariectomized ewe as a model. The objectives of the in vitro work were to determine if a four hour challenge with insulin, glucagon or a combination of both insulin and glucagon would lead to a reduction in the relative abundance of CYP2C39 or CYP3A13 mRNA, as well as a decrease in the enzymatic activities of CYP3A and CYP2C subfamilies. A dose dependent decrease (P < 0.05) in CYP2C and CYP3A activity was observed in hepatocytes challenged with increasing concentrations of insulin, while a challenge with glucagon had no effect on cytochrome P450 2C or 3A activity. Cytochrome P450 2C activity was decreased (P < 0.05) during exposure of cells to 1.0 nM insulin and 0.1 nM glucagon as well as 0.1 nM insulin and 1.0 nM glucagon. Cells cultured with 1.0 nM insulin and 0.1 nM glucagon showed a trend ( P < 0.10) for a decrease in CYP3A activity. The relative abundance of CYP2C39 and CYP3A13 mRNA showed no response to insulin, glucagon or a combination of insulin and glucagon exposure. These data support a model in which the known insulin-induced decrease in progesterone catabolism is a result of a reduction in CYP2C and CYP3A activity. The objectives of the in vivo experiment, utilizing ovariectomized ewes, were to determine if supplementing feed with either sodium acetate or sodium propionate altered insulin secretion, hepatic activity of cytochrome P450 2C and 3A, and/or progesterone clearance. Sixteen ovariectomized ewes were fed 3 kg/d for 10 d, a diet consisting of 50% corn silage, 38% triticale haylage, 12% soy bean meal, and 200 mL of 3.5 M sodium acetate (energy control n = 8) or 2.0 M sodium propionate (gluconeogenic substrate; n = 8). Insulin concentrations were determined directly before feeding and at 15, 30, 60, 90, 120, 180, 240, and 300 min. Progesterone clearance from peripheral circulation was measured by giving a 5 mg injection of progesterone into the left jugular vein and collecting blood via the right jugular vein at 2, 4, 6, 8, 10, 15, 20 and 30 min afterwards. Liver biopsies were taken one hour after feeding and used for determination of cytochrome P450 2C and 3A activities. Insulin concentrations in ewes supplemented with sodium propionate were elevated (P < 0.05) at 15, 30 and 60 minutes after feeding compared to the sodium acetate group. Cytochrome P450 2C and 3A activity were decreased (P ≤ 0.05) 1 h after feeding in the sodium propionate treatment relative to sodium acetate treatment. Clearance of progesterone from the peripheral circulation, one hour after feeding, was similar between treatment groups, as well as the average fractional rate constant of progesterone clearance (k). Elucidating a mechanism to decrease progesterone catabolism, thereby increasing concentrations of progesterone, seems a logical approach to ameliorate high rates of embryonic loss without compromising dry matter intake.

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