Effects of fasting on blood plasma levels, metabolism and metabolic effects of epinephrine and norepinephrine in steers.

Experiments were designed to study effects of 3 days of fasting on blood plasma levels, metabolic clearance rates (MCR) and effects of norepinephrine (NE) and epinephrine (E) on levels of glucose, nonesterified fatty acids (NEFA) and immunoreactive insulin (IRI) in 12 steers. During fasting, levels of E, NE and protein did not change, whereas IRI, T3 and glucose decreased and NEFA, acetoacetate and beta-hydroxybutyrate increased. Before and at the end of fasting, NE or E were iv infused for 120 min. NE and E were elevated after 15 min and to the end of the infusion. The increase in E, but not in NE, was significantly greater after 3 days of fasting than before fasting (P less than 0.05). MCR for E was lower after fasting (299 +/- 17 vs 204 +/- 10 ml.kg-0.75.min-1; P less than 0.001), whereas MCR for NE was not significantly different (455 +/- 37 vs 400 +/- 27 ml.kg-0.75.min-1). MCR was higher for NE than for E, both before and after fasting (P less than 0.05). After the infusion, E and NE decreased within minutes to pre-infusion concentrations. During E infusions, NEFA increased significantly more, whereas glucose increased less in fasted than in fed animals. During NE infusions, NEFA increased in fasted, but not in fed animals, and glucose increased less at the end than before fasting. IRI decreased during E infusions only in fed animals, and transiently increased after the infusion, except after NE infusion in fasted steers.(ABSTRACT TRUNCATED AT 250 WORDS)