Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

Albert H. Meier

Abstract

Studies were made in Japanese quail (Coturnix c. japonica) to determine if daily variations of plasma insulin and de novo lipogenesis exists and examine the roles of daily variations in lipogenic responsiveness to insulin and prolactin. A daily variation in plasma insulin levels exists in quail fed ad libitum, with photophase levels 4.6 times greater than scotophase levels. This variation was not driven exclusively by the feeding of the quail, because insulin levels had dropped by dark onset, yet all bird's crops contained food at this time. There was a daily variation in the amount of $\sp{14}$C-acetate labelled lipids extracted from the liver and fat pads (FP). Liver $\sp{14}$C-acetate incorporation into lipids was lowest at 10:00 h and peaked from 18:00 to 22:00 h. A similar pattern of lipogenesis was observed in birds injected with bovine insulin. A difference exists between the trough and the peak of lipogenesis in insulin injected birds. FP $\sp{14}$C-labelled lipid content was constant throughout the 24-hour period, with a depression at 22:00 h. Injections of bovine insulin depressed in vivo lipogenesis at all times-of-day (TOD). There was no change in sensitivity at different TOD, because bovine insulin injections depressed lipogenesis similarly at each TOD. Injections of chicken insulin did not alter lipogenesis as measured by $\sp{14}$C-labelled lipid in the liver and FPs. Attempts to alter in vivo lipogenesis with the D2 type dopamine agonist, 2-bromo-$\alpha$-ergocryptine, used previously to reduce fat stores, cholesterol and triglyceride levels in mammals, were unsuccessful in quail. Food and water intake, body weight (BW), liver and FP weight, and $\sp{14}$C-acetate incorporation into liver and FP were unchanged. It is not known why quail react differently than mammals to this drug. Injections of ovine prolactin or saline for 5 days produced BW changes in quail. Prolactin injected birds gained 5.4 g, non-injected birds gained 2.4 g, and saline injected birds lost 3.9 g of BW. BW changes were not due to differences in FP weights. TOD effects within each group were lacking, with all injection times producing similar results.

Pages

102

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