Microradioisotopic assay for indoleamine N-methyltransferase and analysis of products by liquid chromatography

A rapid method for the separation of tryptamine, 5-hydroxytryptamine, and their N-methylated derivatives is described. The method involves liquid chromatography using a cation exchange column with the eluant monitored either by ultraviolet or fluorescence spectroscopy. The latter technique permits the detection of picogram quantities of indoleamines. Using normal-phase liquid chromatography a complete separation of tryptamine, its N-methylated derivatives, and their β-carboline analogs was also achieved. A radioisotopic assay with the potential to detect indoleamine N-methyltransferase activity in milligram quantities of rabbit lung tissue was developed. The radioisotopically labeled products formed from a number of substrates in such assays were characterized by liquid chromatography.     

Low levels of anterior tibial loading enhance knee extensor reflex response characteristics.

We examined whether neuromuscular reflexes were altered with anterior loads applied to the tibio-femoral joint. A ligament testing device was modified by attaching a reflex hammer to a steel mounted frame to illicit a patellar tendon tap, while anterior directed loads displaced the tibia on the femur. Five trials were acquired while anterior-directed loads (20, 50, 100 N; counterbalanced) were applied to the posterior tibia between 20 N pre (20 N(Pre)) and post (20 N(Post)) baseline conditions on two different days. Surface electromyography (sEMG) recorded mean quadriceps (Q) and hamstring (H) reflex time (R(Time)=ms) and reflex amplitude (R(Amp)=%MVIC). A load cell on the anterior tibia measured the timing (KE(Time)=ms) and amplitude (KE(Amp)=N) of the knee extension force, and was used to calculate electromechanical delay (EMD=ms) and peak knee extension moment (KE(Mom)=Nm/kg). Data from 19 recreationally active subjects revealed good to excellent response consistency between test days and between baseline conditions for R(Time), R(Amp), KE(Time) and KE(Amp). With anterior tibial loading, R(Time) was faster at 50 N vs. 20 N(Post), and R(Amp) was greater at 20 N(Pre) vs. 20 N(Post) (Q and H) and at 50 N vs. 100 N (Q only). KE(Mom) was greater at 20 N(Pre) and 50 N vs. 20 N(Post), and EMD was shorter at 50 N vs. 20 N, 20 N(Pre) and 20 N(Post). These results suggest that knee extensor reflex responses are enhanced with low (50 N) but not moderate (100 N) anterior loading of the knee.