Meal-contingent intestinal lymph sampling from awake, unrestrained rats

Standard procedures for intestinal lymph collection involve continuous, quantitative drainage of the lymph fluid in anesthetized or restrained animals that are often euthanized within 48 h. We here describe a novel technique for the nonocclusive cannulation of the major intestinal lymph duct in rats that allows for repetitive in vivo sampling of intestinal lymph from unrestrained, awake, and ad libitum-fed animals. The distinctive feature of this novel technique is that a 5- to 7-mm long piece of Vialon tubing (OD/ID: 0.8/0.7 mm) with a small hole in its wall is first implanted into the major intestinal lymph duct for stabilization. The tapered tip (OD: ≈0.1 mm) of the catheter is then inserted into the hole of the tubing and fixed in place with a polyamid suture and a drop of tissue glue. In our hands, catheters implanted this way remain patent for up to 6 wk after surgery. In an initial experiment we collected lymph from six adult rats before (0) and 15, 30, 45, 60, 75, 90, 120, and 180 min (120 μl, each) after the onset of isocaloric (12.5 kcal) low-fat (LF) or high-fat (HF) test meals and measured active glucagon-like peptide-1 (GLP-1). Intestinal lymphatic GLP-1 concentration increased (P < 0.05) from ≈4 pmol/l (0 min) to a peak of 33 ± 6 (means ± SE) or 22 ± 4 pmol/l at 15 (HF) or 30 min (LF) after meal onset and gradually returned to baseline levels by 180 min. With this new technique fewer animals are required to generate physiologically relevant data for various aspects of gastrointestinal physiology that involve the lymphatic system. Furthermore, the advantage of this system is that the animal can act as its own control when the effect of different experimental protocols is tested.