Leptin-mediated inhibition of the insulin-stimulated increase in fatty acid uptake in differentiated 3T3-L1 adipocytes.

The effects of insulin and leptin on fatty acid uptake in differentiated (adipocytes) and undifferentiated 3T3-L1 cells were investigated. It was demonstrated that in undifferentiated 3T3-L1 cells, insulin and leptin have no effect on fatty acid uptake. In differentiated 3T3-L1 adipocytes, insulin had a concentration-dependent stimulatory effect on fatty acid uptake, whereas leptin on its own had no effect. Leptin, when coincubated with 10 nmol/L insulin, resulted in a concentration-dependent inhibition of the insulin-stimulated fatty acid uptake in differentiated 3T3-L1 cells. These results indicate that leptin has a direct inhibitory effect on the stimulation of fatty acid uptake by insulin in differentiated murine adipocytes.

Gabapentin inhibits the substance P-facilitated K(+)-evoked release of [(3)H]glutamate from rat caudial trigeminal nucleus slices.

The effect of gabapentin on the release of the spinal sensory neurotransmitter glutamate has been investigated in an in vitro model using a perfused thin slice preparation from the rat brainstem containing the spinal trigeminal caudal subnucleus (Sp5C) and pre-incubated with [(3)H]glutamate. Addition of excess K(+) to the perfusing solution increased the content of tritium in the perfusate. The prior addition of substance P increased this index of glutamate release in a concentration-dependent manner, with the mean maximum of around 50% increase obtained at 1-3 microM. The action of substance P to increase the evoked release of glutamate was blocked by the antagonist CP-99994, suggesting a specific involvement of the NK(1) receptor in mediating the facilitatory effect. On its own, gabapentin at up to 100 microM did not modify the baseline level of K(+)-evoked release of glutamate; however, gabapentin caused a concentration-dependent decrease of the facilitatory effect of substance P (EC(50)=6.49 microM). The R-(-)- and S-(+)-isomers of 3-isobutylgaba were then tested against the increase in K(+)-evoked release of glutamate by substance P. S-(+)-3-isobutylgaba (pregabalin) at 30 microM acted like gabapentin to reduce the substance P-mediated increase of release almost to the baseline level of K(+)-evoked release, while in contrast the R-(-)-isomer at this concentration produced no reduction, and rather a trend towards a further enhancement of the potentiating effect of substance P. In conclusion, we have found and characterized an effect of gabapentin that is of possible mechanistic relevance to the anti-hyperalgesic/allodynic actions of this compound.