Morphological observations on the fate of liposomes in the regional lymph nodes after footpad injection into rats

Multilamellar liposomes composed of equimolar egg phosphatidylcholine and cholesterol and containing carboxyfluorescein or colloidal gold were injected subcutaneously into the footpad of the hind-leg of rats. The draining popliteal lymph nodes of animals killed at time intervals after injection were then dissected and sections examined by fluorescence microscopy (carboxyfluorescein), light microscopy using an immunogold silver kit to enhance gold particles or by transmission electron microscopy. Morphological observations confirmed that subcutaneously injected liposomes accumulate in large numbers in the draining lymph node. The majority of liposomes arrived at the subcapsular sinuses, probably via afferent lymphatic vessels, as such, i.e., in a non-cell bound form. Subsequently, liposomes were dispersed throughout the lymph node either by permeation as free vesicles along the sinuses or by cells involved in vesicle uptake. The majority of such cells were free macrophages, littoral cells and reticular cells (fixed macrophages). Once within cells, liposomes were seen digested by the lysosomal apparatus with varying loss of their lamellar structure, leaving free gold particles within the lysosomes.

The role of the gut in regulating food intake in man

In addition to various psychosocial and metabolic factors, food intake is also influenced by gastrointestinal mechanisms that trigger both the initiation and termination of eating behaviors. Although gastric distension is one of the most obvious signs of "fullness" and clearly plays a role in controlling food intake, its effects are only temporary and are distinct from the feelings of satiety generally associated with a meal. Such postprandial sensations appear to be related to the activation of intestinal chemoreceptors. Other evidence indicates that the release of cholecystokinin and perhaps other transmitters as well may contribute to satiety. Although the stomach probably does not expand or shrink in response to different levels of food intake, nutrient receptors in the small intestine probably do adapt to changes in food intake. Intestinal adaptation also occurs in response to thyroid hormone, insulin, and cortisol as well as to obesity, pregnancy, and illness, which all may have an important bearing on changes in eating behavior in these situations.