Intestinal transport of antibodies in the newborn rat

The transmission of -125-I-labelled immunoglobulin G by proximal and distal regions of the small intestine of 16-day-old rats

1. Standard doses of -125-I-labelled rat IgG were injected into the intestinal lumen of rats aged 16 days, and their sera were sampled 2 and 3 hr later. High concentration quotients were obtained after injection into the proximal small intestime, whereas very little immunoglobulin was transmitted from doses injected into the terminal 20 cm of the small intestine. 2. The villi of the terminal 18--20 cm of the small intestine of 16-day-old rats, the region from which very little transmission of IgG occurred, were lined by tall columnar absorptive cells with very larg supra-nuclear vacuoles. The extent of the terminal intestine, in which this cell type predominated in the absorptive epithelium, varied with age. The importance of defining the precise location of the region of the intestine under examination is stressed. 3. The experimental results and the histological observations are discussed in relation to (a) the results which have been obtained using PVP, which is unsuitable as an indicator of immunoglobulin transport in the rat and (b) the histological composition of the absorptive epithelium and the maturation changes which affect the epithelium between 18 and 21 days.

The attachment of IgG to cell components: a reconsideration of Brambell's receptor hypothesis of protein transmission

Nuclear, mitochondrial and microsomal fractions were prepared from rabbit yolk-sac splanchnopleur and rabbit chorio-allantoic placenta, and tested in vivo and in vitro for attachment of labelled rabbit and bovine IgG. Similar fractions were prepared from small intestinal scrapings of neonatal rats, and tested in vivo and in vitro for attachment of labelled rat and sheep IgG. In all cases the attachment of the homologous and heterologous proteins was substantially equal. Digestion experiments on the labelled organelle pellets of rabbit yolk-sac were carried out with the proteases of the macerated tissue (the cell sap or final supernatant) at optimum pH. The nuclear pellet gave rise to a higher proportion of breakdown products derived from bovine than from rabbit IgG, showing the existence of a mechanism whereby selection between the two proteins might be brought about.

The absorption of 125I-labelled immunoglobulin G by different regions of the gut in young rats

1. (125)I-labelled homologous IgG was injected into different regions of the small intestine of rats aged 12, 16, 18, 20 and 22 days. At 12 days the proximal and middle regions of the intestine readily absorbed globulin and transmitted it to the circulation. The distal region of the intestine transmitted little to the circulation at all ages tested.2. The intestine loses its ability to transmit globulin to the circulation in a distal-proximal direction. At 16 and 18 days the ability of the middle region had declined significantly, and this decline continued so that little globulin was transmitted from this region at 20 and 22 days.3. The proximal intestine retained the ability to transmit globulin to the circulation in significant amounts up to 20 days.4. There is a close negative correlation between body weight and total radioactivity of the sera of rats which had received doses of labelled globulin into the proximal and middle regions of the intestine. There was no such correlation after injection into the distal intestine - suggesting a restricted throughput of radioactive material by the absorptive cells of this region.5. These results are discussed in the context of the termination of antibody absorption, and in relation to the results obtained using polyvinyl pyrrolidone.

Isoelectric focusing analysis of transmission of fractions of bovine IgG across the gut of the suckling rat

Twelve-day-old rats were fed a mixture of fast and slow chromatographically prepared fractions of bovine IgG, labelled with ¹²⁵I and ¹³¹I. The pooled young rat sera were submitted to analysis by electrofocusing. The results show a wide variation of concentration quotients between the different pI peaks of IgG, with the more basic fractions being transmitted more readily in both fractions. One slow IgG peak (pI 7.8) in particular is transmitted very readily. These findings reinforce the concept of selectivity in transmission.

The possible use of the young rat gut as a test for protein integrity is discussed.

The effects of cortisone acetate on stomach evacuation and the absorption of 125I-labelled globulins in young rats

1. After short exposure (3-5 hr) to I.P. cortisone acetate (5 mg), the reduced transmission of labelled globulin to the circulation in 14-day-old rats is due to the slow release of the oral dose from the stomach. The ability of the small intestine to absorb and transmit globulin to the circulation is comparable in control and experimental animals.2. About 26 hr after cortisone acetate treatment (5 mg), the greatly reduced absorption of labelled globulin from oral doses administered to rats aged 15 days is due to the combined effects of the slower release of the dose from the stomach and to changes which have occurred in the small intestine.3. About 50 hr after the administration of 5 mg cortisone acetate the effect on the rate of stomach evacuation is minimal in rats aged 16 days. When labelled globulin is introduced directly into the duodenum of these animals virtually no absorption occurs.4. The results obtained from the experiments in which labelled globulin was injected into the duodenum support the contention that the proximal half of the small intestine is an important site for macromolecular transport.