Glucose is the most important energy substrate for the maintenance of tissues function. The liver plays an essential role in the control of
glucose production, since it is able to synthesize, store, and release
glucose into the circulation under different situations.
Hormones like
insulin and
catecholamines influence hepatic
glucose production (HGP), but little is known about the role of the central actions of physiological doses of
insulin in modulating HGP via the autonomic nervous system in nonanesthetized rats especially in SHR where we see a high degree of
insulin resistance and metabolic dysfunction. Wistar and SHR received ICV injection of
insulin (100 nU/μL) and hepatic venous
glucose concentration (HVGC) was monitored for 30 min, as an indirect measure of HGP. At 10 min after
insulin injection, HVGC decreased by 27% in Wistar rats, with a negligible change (3%) in SHR. Pretreatment with
atropine totally blocked the reduction in HVGC, while pretreatment with
propranolol and
phentolamine induced a decrease of 8% in HVGC after ICV
insulin injection in Wistar. Intracarotid infusion of
insulin caused a significant increase in subdiaphragmatic vagus nerve (SVN) activity in Wistar (12 ± 2%), with negligible effects on the lumbar splanchnic sympathetic nerve (LSSN) activity (-6 ± 3%). No change was observed in SVN (-2 ± 2%) and LSSN activities (2 ± 3%) in SHR after ICA
insulin infusion. Taken together, these results show, in nonanesthetized animals, the importance of the parasympathetic nervous system in controlling HVGC, and subdiaphragmatic nerve activity following central administration of
insulin; a mechanism that is impaired in the SHR.