Passage of Insulin and Inulin Across Vascular Membranes in the Dog

The equilibration of IRI and NSILA between arterial plasma and lymph was studied at different sites in sixteen anesthetized dogs. Lymph was collected from the thoracic duct in one group, from the main hepatic lymph vessel in another, and from the leg lymphatic in a third group. No baseline gradients were observed between arterial serum and lymph IRI concentrations. Lymph/serum NSILA concentration ratios were 0.62 ± 0.29 for leg lymph, 0.66 ± 0.20 for thoracic duct lymph and 0.84 ± 0.63 for hepatic lymph. Two tests were carried out in each dog: (1) IVGTT (0.5 gm./kg.) Evans Blue was injected concurrently in some cases. Net glucose disappearance rate and serum IRI and NSILA patterns were similar in the three groups. Serum IRI passed rapidly into hepatic and thoracic duct lymph reaching plateau levels of 40 and 35 μU. per ml. respectively within 15 min. Leg lymph glucose concentration increased immediately but IRI appearance was delayed: A plateau of 20 μU, per ml. was reached after 30 min. No significant passage of Evans Blue into paw lymph was observed. Glucose injection was followed by a significant decrease in serum NSILA. Hepatic and thoracic duct lymph NSILA levels decreased slightly but NSILA concentration remained unchanged in leg lymph. (2) One hour after the first test 0.2 U. per kg. of pork insulin and 25 uc 14C-inulin were injected intravenously. The patterns of distribution of these two substances were similar. Both reached peak concentrations first in hepatic lymph then in thoracic duct lymph. In paw lymph their appearance was delayed and the maximum concentration achieved was lower. It is concluded that differences in capillary permeability are likely to determine in part the distribution of IRI and NSILA in body fluids and thus may influence their biological activity.

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