Effect of reproductive status on uptake of latex microparticles in rat small intestine.

This study investigates whether pregnancy or lactation affects microparticle uptake across the small intestinal mucosal barrier, since aspects of gastrointestinal physiology such as motility may be altered in these conditions. It also reports on validation of the model by several methods and discusses the findings in relation to possible mechanisms. Anaesthetised, pregnant, lactating, virgin female or male adult rats were gavaged with fluorescent latex microparticles. The small intestine was removed and fixed either 5 or 30 min later and successive segments of equal length were examined with fluorescence microscopy. Minor adjustments were made to experimental methods to explore details of the uptake mechanism. Control sections contained no particles. All experimental samples showed luminal and surface particles and also contained particles within the tissue, most associated with villous absorptive enterocytes. Particle uptake was greatest at the 30-min time-point, when maximum uptake was usually in the proximal jejunum; although in the early lactating group, this was shifted distally. Total tissue uptake was increased in pregnant and early lactating groups, mainly at villous absorptive and mucus-secreting cells. Accumulation and progression of particles was reflected in increased numbers in the lamina propria. These data were validated by several methods, including particle detection in the blood and mesenteric lymph nodes in some groups. At both time-points, uptake profiles for pregnancy and early lactation differed from those of other groups, implying possible links between particle uptake and hormone levels, surface mucus and tight junction patency.