In vivo electron spin resonance in rats

Abstract

In vivo ESR studies have been made on Wistar and Sprague-Dawley rats using travelling wave helices implanted in the left lobe of the liver. Tissue regenerates completely around the Teflon-enclosed turns of the coil and histological studies have shown that it is composed of liver cells and connective tissue. Electron spin resonance studies of this tissue in vitro reported by Commoner and Ternberg in 1961 have demonstrated that it exhibits the 'tissue radical' signal. The implanted coils have detected, in vivo, a three-line spectrum due to a strong concentration of 4-hydroxy- 2,2,6,6-tetramethylpiperidine-1-oxyl free radical ('tempol'), a nitroxide spin label, injected either intramuscularly, intraperitoneally or intravenously into the experimental animal immediately prior to the measurement. They have also detected, in vivo, a similar three-line spectrum due to 'spin-labelled chlorpromazine', a tranquillizing drug to which this nitroxide spin label has been attached, injected intramuscularly or intraperitoneally into the animal immediately prior o the measurement. Work is currently in progress to increase the in vivo sensitivity of the implanted helices by menas of improved coupling techniques and the use of a time-averaging computer.

The evolution of biomedical EPR (ESR)

“…The contemporary pioneering experiment was reported by Piette and colleagues in 1975 at the University of Hawaii [30]. They implanted a helix resonator in the liver of a rat and administered high doses of the piperidine nitroxide TEMPOL (or 1-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl).…”

“…This is basically incorporating the compounds, aminoxyl (aka nitroxide) radicals that are used in spin labeling, but targeting them (if possible) to specific regions of the body, organs, etc. In fact, the work from the Piette group was one of the earliest examples [30]. We initially worked on the same X-band system after Piette trying to measure EPR at the carotid artery in a rat, but realized quickly that the microwave heating at 9.5 GHz was a real issue [unpublished results].…”

“…The first reports of an in-vivo L-band experiment (vs. minimally invasive X-band experiments from the Piette group discussed earlier [30]) was in the early 1980s by S.J. Lukiewicz and S.G. Lukiewicz at the Society of Magnetic Resonance Meeting in 1984 and an International Pigment Cell Conference [65], where the authors detected the in-vivo EPR spectrum of melanin radicals in melanoma tumor cells implanted in the tail of a mouse.…”

Detection of bioradicals by in vivo L‐band electron spin resonance spectrometry

“…Probably the most controversial concern in this regard relates to the vast number of ESR measurements made on excised tissue or cell suspensions. In order to answer this question, Feldman et al 4 reported one of the first in vivo ESR studies on a modified X-band ESR instrument employing a traveling wave helix structure in place of the standard microwave cavity. They reported the first in vivo ESR study in the liver of intact rats.…”

“…According to Piette and coworkers, 4 the ideal in vivo ESR spectrometer was one in which a live animal could be directly accommodated, which was virtually impossible with commercial X-band microwave spectrometers operating at 9.4 GHz. The instrumental requirements for in vivo animal studies are two-fold: (1) a resonant device with dimensions suitable to fit the body of small animals; and (2) a choice of an operating frequency that does not produce dielectric heating, like a microwave oven.…”