Effect of selective hepatic vagotomy on plasma FFA levels in resting and exercising rats

Abstract

Metabolic effects of a selective hepatic vagotomy (HV) were investigated in nonfasted (N) and 24-h fasted (F) rats, at rest and immediately after a 50-min exercise period (26 m/min, 0% grade). In nonfasted rats, no significant differences between HV and sham-operated (SHM) groups were found in blood substrates [free fatty acids (FFA) or glucose], insulin, and muscle glycogen levels, either at rest or after exercise. In F rats, liver glycogen was almost completely depleted at rest. This depletion was associated with a significantly (P less than 0.05) lower plasma FFA concentration at rest in HV compared with SHM rats (mean +/- SE, 0.57 +/- 0.04 vs. 0.83 +/- 0.1 mmol/l). No differences in FFA levels were observed between the same two groups after the exercise period. Exercise, however, resulted in a 2.5 times greater glycogen breakdown in the soleus muscle of HV compared with SHM rats. Hepatic vagotomy in the F condition was also associated with lower resting and exercising insulin concentrations. It is concluded that HV, when followed by a 24-h fast, may influence metabolic substrate regulation at rest and to a certain extent during exercise. These data support the concept of the existence of hepatic glucoreceptors responsive to a decrease in liver glycogen content.

The effects of stimulation and lesioning of afferent nerves on blood glucose and free fatty acid contents in rats in conditions of changing glycemia

“…Rats treated with neurotoxic doses of capsaicin showed decreases in basal FFA levels. These results are in good agreement with data showing decreases in plasma FFA concentrations after hepatic vagotomy in starved rats at rest [14]. Attention is drawn to the decrease in the magnitude of changes in blood FFA due to doses of insulin in rats with lesioned capsaicin-sensitive nerves, which is evidence for the development of resistance to insulin also affecting its action on FFA.…”

Effects of inducing physiological hyperglucagonemia on metabolic responses to exercise

“…Three days before the experimentation, all rats underwent a jugular vein cannulation under pentobarbital sodium (40 mgAEkg )1 ip) anesthesia. The jugular catheter was implanted by a method described previously (Lavoie et al 1988). This catheter was used for glucagon or saline infusion and rapid anesthesia (iv) of rats at the end of the acute exercise or in the resting state.…”

Lack of Effects of an Acute Hepatic Vagotomy on Insulin and Catecholamine Responses in Rats Following Exercise

“…When there was any ambiguity concerning the identification of the vagal hepatic branch, the subject was discarded from the experiment. In addition, in a separate experiment, the increased insulin response to an acute hepatic vagotomy in adrenalectomized rats was used as a further assessment of the surgical technique (Lavoie et al, 1988(Lavoie et al, , 1989. Accordingly, an ≈ 36% increase in peripheral venous insulin concentrations and an ≈ 58% increase in portal venous insulin concentrations were found 30 min after section of the hepatic vagus nerve (Trabelsi et al, 1995).…”

“…Food was removed from cages 14 h before the experiment, which took place 24 h after the last exercise bout for the TR rats. On the day of the experiment, all rats were first anesthetized (pentobarbital sodium; 40 mg/kg, ip) then implanted with a jugular catheter as previously described (Lavoie et al, 1988). The animals were then allowed a 30 min rest period to stabilize their metabolic and hormonal state.…”

“…In the past few years, our laboratory has reported repeated evidence that the liver, through the hepatic branch of the vagus nerve, contributes to the hormonal response of exercise (Lavoie et al, 1988(Lavoie et al, , 1989Cardin et al, 1991Cardin et al, , 1994. The effect of physical training in this afferent hepatic contribution, however, has never been considered.…”