This study was designed to test how extended exposure of lenses to sera with different ionic strengths influences the distribution of ions and water in the lens. Pig lenses were incubated in cold sera (0 degree C), which were adjusted to variable concentrations of NaCl, and their K+, Na+, Cl-, and water contents were measured. Incubation at 0 degree C inhibits active transport processes and thereby allows equilibration of the mobile ions and water. The hypothesis was that lens water content (volume) would follow the ion-induced protein changes predicted by a model derived from previous osmotic studies on proteins. As expected, exposure of the lens to cold caused a gain of sodium and a partial loss of potassium. However, the potassium concentration in the lens remained several fold higher than that in the bathing solution (about 41 vs. 1.8-4.6 mM/kg H2O), indicating that a portion of the potassium within the cold-exposed lens was not free to diffuse. That the water content of the lens showed a negative rather than a positive relationship with the concentration of NaCl within the lens was explained by the idea that an increase in NaCl within the lens (up to at least 250 mM/kg H2O) causes a decrease in the osmotically unresponsive water volume associated with lens proteins.

Animals↗

PubMedDate not supplied

Proton relaxation enhancement associated with iodinated contrast agents in MR imaging of the CNS.

PURPOSE: To study the effects of iodinated radiographic contrast agents on proton relaxation in MR imaging. PATIENTS AND METHODS: Two patients were evaluated after the intrathecal administration of an iodinated nonionic contrast agent (Isovue) and five subjects with cranial tumors following the intravenous administration of an iodinated ionic contrast medium (Renografin). RESULTS: Both patients with subarachnoid iodinated contrast media demonstrated a relative reduction in T1 and/or T2 times using a spin-echo sequence, while four of five of the subjects with intracranial tumors (one glioma, one dural metastasis, three meningiomas) and intravenous enhancement revealed a visible MR effect. Confirmation of these in vivo observations was obtained by in vitro measurement of T1 and T2 while varying the concentration of the contrast media in saline. All iodinated contrast media showed progressively reduced relaxation times (T1 and T2) as the concentration of the agent was increased. The largest contributing relaxation mechanism is probably due to the binding and exchange of the surrounding water with the contrast molecules. CONCLUSION: The observed T1/T2 effects suggest that administration of iodinated contrast media in the period immediately prior to MR scanning may be contraindicated in selected cases due to the demonstrated alteration of MR signal intensity that may lead to diagnostic inaccuracies.

Brain Neoplasms↗