Stability of lipid vesicles in tissues of the mouse: a gamma-ray perturbed angular correlation study.

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Abstract
The rate of phospholipid vesicle disruption in specific tissues of the mouse was followed by .gamma.-ray perturbed angular correlation (PAC) spectroscopy. In these studies, high levels of 111In-nitrilotriacetic acid complex are contained in unilamellar vesicles consisting of distearoyl phosphatidylcholine, cholesterol, and small amounts of other lipids which modify the surface properties. The PAC technique monitors the extent of vesicle breakup by measuring a time-integrated perturbation factor, < G22(.infin.) >. As the vesicles are broken open in vivo, the released 111IN3+ ions quickly bind to macromolecules and the < G22(.infin.) > value decreases substantially. After administration of vesicles by various routes (i.v., i.p., s.c., and oral), the radioactivity and < G22(.infin.) > values were determined for several tissues at intervals up to 24 h. Evidently, the PAC technique in conjunction with standard .gamma. counting methods provides unique information on the condition and location of vesicles in specific tissues, significant differences in vesicle integrity are found in various tissues and both the means of administration and the presence of surface charge affect the vesicle stability and distribution. The carbohydrate analog of cholesterol affect vesicle stability but not distribution.