EFFECT OF ANESTHETIZING THE REGION OF THE PARAVENTRICULAR HYPOTHALAMIC NUCLEI ON ENERGY-METABOLISM DURING EXERCISE IN THE RAT

The ventromedial and posterior hypothalamic nuclei are known to influence glucoregulation during exercise. The extensive projections of the paraventricular hypothalamic nucleus (PVN) to the sympathetic nervous system suggest that the PVN also may be involved in glucoregulation during exercise. The region of the PVN was anaesthetized with bupivacaine before running (26 m min(-1)) or continued rest, via previously implanted bilateral brain cannulas aimed at the dorsal aspect of the PVN. Control rats were treated identically to PVN-anaesthetized rats, but were not infused. Blood, for determination of plasma concentrations of metabolites and hormones, was drawn from a tail artery, and H-3-glucose was infused in a tail vein for glucose turnover determinations. At rest, no significant changes in plasma concentrations of metabolites or hormones were induced by anaesthesia of the region of the PVN. During exercise, glucose production and utilization and plasma concentrations of glucose, lactate, glycerol, noradrenaline, adrenaline, corticosterone, and glucagon increased (P <0.02) and plasma insulin decreased (P <0.02) in all rats. However, initially in exercise, adrenaline (4.3 f0.8 vs. 7.9 +/- 1.0 nmol l(-1) in controls, P <0.05, t = 6 min) and later corticosterone levels (1.37 +/- 0.06 vs. 1.69 +/- 0.10 nmol(-1) in controls, P <0.05, t = 20 min) were attenuated by PVN anaesthesia. Initially during exercise, glucose utilization was higher and plasma glucose lower in PVN-anaesthetized rats compared to controls (16.6 +/- 0.8 vs. 12.7 +/- 0.6 mu mol min(-1) 100 g(-1) and 7.1 +/- 0.2 vs. 8.1 +/- 0.2 mmol l(-1), respectively. P <0.05, t = 6 min) and exercise-induced liver glycogen breakdown was only significant in the controls. In conclusion, the region of the PVN does not influence glucoregulation at rest, but affects glucoregulation during exercise, by stimulating adrenaline and corticosterone secretion during exercise.