Nonesterified Fatty Acids and Glucose in Lactating Dairy Cows: Diurnal Variations and Changes in Responsiveness During Fasting to Epinephrine and Effects of Beta-Adrenergic Blockade

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Abstract
To examine whether the typical nightly rise of nonesterified fatty acids in highyielding dairy cows is due to enhanced sympathoadrenal activity, the .beta.-adrenergic blocker, propranolol, was infused from 1800 to 0805 h. Concentrations of nonesterified fatty acids continuously increased, whereas those of glucose and insulin decreased. Nonesterified fatty acid concentration decreased within minutes in response to concentrate feeding, starting at 0700 h, in association with an increase of insulin and glucose. In a second experiment, adrenaline (.82 .mu.mol/kg/min) was infused from 1800 to 1810 h, 0600 to 0610 h, and 0600 to 0610 h on the 1st, 2nd and 3rd d. After the second infusion, food was withdrawn for 23 h. Concentrations of adrenaline increased similary. Nonesterified fatty acids and glucose responses were higher during the second than the first infusion. During fasting, nonesterified fatty acid concentrations increased, whereas glucose and insulin concentrations decreased. During the third infusion nonesterified fatty acids responses were unchanged, whereas glucose responses were decreased. Thus, the nightly rise of nonesterified fatty acids was not the consequence of enhanced .beta.-adrenergic activity. Responses of glucose and nonesterified fatty acids to adrenaline exhibited diurnal differences. Responses of glucose to adrenaline were reduced within 1 d of fasting, whereas those of nonesterified fatty acids were not altered.

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