Summiry. The intestine of the foetal lamb was exposed to large quantities of V-globulin (IgG) by prolonged intra-duodenal infusion, and absorption of intact IgG, with transfer to the lymph, continued undiminished. i.e-, there was no evidence of closure. The rate of proliferation of the intestinal epithelium of the foetal and newborn lamb was measured using mitotii: indices and localised labelling wiih ('H)-thymidine (TdR). In the foetus, cell division in the crypts occurs at a lower rate than the newborn (p<0 (X)l) and there is very slow replacement of ihe intestinal epithelium. In the newborn lamb, a portion of the small intestine was incubated in vivo with TdR and the progress of labelled cells from the crypts upwards along the vitii estimated, using autoradiography of serial biopsies from the same animal. A front of mature, digestive epithelium could be seen advancing up the villi, displacing the immature foetal lype of cell which was capable of transfer of intacl IgG to the lymphatics of the intestine. The evidence presented supports the hypothesis that immediately after birth the intestinal epithelium of the lamb begins to be replaced by a digestive type of cell, and the layer of eells responsible for absorption of cotostral antibodies progressively disappears from the villi, resulting in closure.
Summary Surgical techniques are described for establishing chronic fistulae in the thoracic, intestinal, lumbar and popliteal lymph ducts of foetal lambs in utero. These fistulae have remained patent and enabled lymph to be collected for periods of up to 5 days. The Iambs have been born spontaneously or delivered by Caesarean section with their fistulae intact and still flowing. Lymph flow rates were 9–18 ml./hour from the thoracic duct, 2.8–8.6 ml. /hour from the intestinal duct, 2.8–9.2 ml./hour from the lumbar trunk and 0.6 ml./hour from the popliteal duct. The protein concentration of foetal thoracic duct lymph was 2.30 g./100 ml. immediately after cannulation, the intestinal lymph 2.37 g./100 ml. and the lumbar lymph 2.12 g./100 ml. The cells of foetal lymph were almost all small and medium lymphocytes and only an occasional cell was found in mitosis. Drainage of the thoracic duct lymph for 36 hours drastically reduced the number of lymphocytes in the lymph, suggesting that, as in the adult sheep, most of the lymphocytes in foetal lymph are recirculating cells.
Thioglycollate broth- and agar-elicited rat peritoneal exudate cells contain copious amounts of agar, a sulphated polysaccharide contained in the eliciting agent; the agar content has been measured chemically by the anthrone method for neutral polysaccharides. Adherence experiments confirm that day-3 thioglycollate-elicited macrophages contain 95% of the measured agar; on day 1, 72% is associated with polymorphonuclear cells. Agar ingestion by macrophages coincides with increases in glycogen synthase activity. We suggest that ingestion of agar may be related to the reported deficiencies in function of thioglycollate-elicited or -treated macrophages.
Summary The kinetics of migration of bone marrow cells to the peritoneal cavity have been studied using in vivo labelling of the marrow of the rat tibia with (methyl‐3H)‐thymidine (*TdR). The incorporation of 3H into DNA is directly related to the amount infused over a thirty‐minute period, though only 2–3% of the infused dose is incorporated into DNA in the bone. Autoradiography has shown widespread labelling of bone marrow cells throughout the tibia. Band cells and polymorphonuclear neutrophils (PMN) show an increase in labelling during the 2–3 days after infusion, confirming the maturation of granulocytes prior to their release to the circulation. The disappearance of 3H‐labelled DNA from the bone occurs rapidly during the 3 days after infusion of *TdR with a half‐life (t½) of 1·4‐1·7 days. There is a concomitant increase in the specific activity of DNA in peritoneal cells elicited by agar, particularly in the macrophage (Mφ), Labelling of PMN in the peritoneal exudate occurs only when agar is injected from 2–4 days after infusion of *TdR. The time for maturation of PMN in the rat bone marrow (BM) (2–3 days) has been confirmed, and the method of labelling permits both measurement of the migration of cells from BM to peritoneal cavity and an estimate of the rates of migration.
Summary Cell suspensions from the bone marrow (BM), spleen, thymus, liver and lymph nodes of 14 foetal lambs from 85‐135 days gestation were incubated in vitro with 3H ‐thymidine (TdR). Cells from the long bones, the humerus, tibia and femur, yielded similar results, viz., (a) the total leucocyte population of the bone increased from a mean of 8 8×106 at 85‐90 days (N = 4) to a mean of 487×106 at 130‐135 days (N = 3); (b) the rate of incorporation of TdR varied from 22460‐45960 c.p.m./h/106 cells with no clear trend related to foetal age; this rate is consistent with active mitosis occurring in the expanding BM cell population; (c) bone weight and cell number/bone increased in parallel, and the total mitotic capacity of the bone showed a similar pattern. In the liver, spleen and thymus the incorporation of TdR per 106 cells decreased during the latter part of gestation. Despite growth of the liver (from 18 g to 71 g), the number of white blood cells (WBC) extracted from this tissue was lower at 135 days than at 85 days, suggesting that the haemopoietic capacit of the liver declined during this period. The marked increase in total WBC numbers in the thymus suggests tihs tissue may be supplying circulating lymphocytes to the growing foetus.
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