In vivo manganese MR imaging of calcium influx in spontaneous rat pituitary adenoma.

Cross DJ, Flexman JA, Anzai Y, Sasaki T, Treuting PM, Maravilla KR, Minoshima S. AJNR Am J Neuroradiol. 2007 Nov-Dec;28(10):1865-71 During a study on aged rats, the authors of this paper found that some of their critters had spontaneously developed pituitary adenomas. Not wanting to waste “bad” animals, they reasoned that they could use these rats to study the calcium-dependent release of hormones with manganese (Mn) enhanced magnetic resonance imaging. Because Mn enters cells through calcium channels, they used Mn as a way to study uptake of calcium in to cancerous neuroendocrine cells. They found that adenomas took up the Mn faster than pituitaries from normal rats, and that they were able to absorb it faster. However, efflux seemed to be about the same between groups from about 2 days on. The increase in pituitary voxel intensity showed dose-dependent decreases when an L-type calcium channel blocker was given intranasally to the rats with almost a complete block at the 3-uL 5mg/mL dose (rat weight not mentioned). Using radioactive fluorodeoxyglucose (FDG) and PET scans, they saw that manganese uptake was greatest in more metabolically active tissue and was correlated with tumor size, though FDG uptake was not as well correlated with tumor size. What I found most interesting about this paper was not addressed in the text; that the signal intensity was still strong (15%ish) even after 10 days. In our own lab we recently saw a rat with an unexpectedly high signal after 12 days, so maybe reading more papers like this could help us figure out where we should be setting our expectations. -DH