Glucose turnover, tolerance and insulin response in wethers, ewes and pregnant ewes in the fed and fasted state

Abstract

Glucose turnover parameters were obtained in fed and fasted wethers, ewes and pregnant ewes in their 2nd and 3rd trimesters, using a jugular bolus injection of D-glucose-2-³H. Fasting significantly (P<0,05) reduced glucose turnover (c. 40%) in both the wether and the non-pregnant ewe. A somewhat larger difference (c. 54%) between the fed and fasted ewes was found in their 3rd trimester of pregnancy due to an increase when fed (c. 29% higher turnover than in the non-pregnant ewe) rather than a decrease when fasted, since there was no statistical difference (P< 0, 1) between glucose turnover values of pregnant or non-pregnant fasted ewes. Glucose tolerance was estimated from an intrajugular glucose load (1 g/kg⁰'⁷⁵ body mass) in these 3 groups of sheep under both fed and fasted conditions, and the resulting insulin response was followed for 4 h after the injection. Fasting reduced the plasma clearance rate of glucose by c. 63% in both the wether and the nonpregnant ewe while the reduction was somewhat smaller (c. 51%) during the 2nd trimester of pregnancy. Only the pregnant ewe group showed a corresponding reduction in the resulting insulin response of 46% which was similar in magnitude to the diminished clearance, indicating that factors other than insulin are responsible for the reduced glucose clearance associated with fasting in the weather and non-pregnant ewe. Despite similar baseline plasma glucose values the glucose load appeared to distribute in a space that was significantly less than that found in all 3 groups of fed sheep when trace amounts were injected.