Nonnutritive flow impairs uptake of fatty acid by white muscles of the perfused rat hindlimb

Abstract

Triglyceride hydrolysis by the perfused rat hindlimb is enhanced with serotonin-induced nonnutritive flow (NNF) and may be due to the presence of nonnutritive route-associated connective tissue fat cells. Here, we assess whether NNF influences muscle uptake of 0.55 mM palmitate in the perfused hindlimb. Comparisons were made with insulin-mediated glucose uptake. NNF induced during 60 nM insulin infusion inhibited hindlimb oxygen uptake from 22.0 ± 0.5 to 9.7 ± 0.8 μmol · g−1 · h−1( P < 0.001), 1-methylxanthine metabolism (indicator of nutritive flow) from 5.8 ± 0.4 to 3.8 ± 0.4 nmol · min−1 · g−1( P = 0.004), glucose uptake from 29.2 ± 1.7 to 23.1 ± 1.8 μmol · g−1 · h−1( P = 0.005) and muscle 2-deoxyglucose uptake from 82.1 ± 4.6 to 41.6 ± 6.7 μmol · g−1 · h−1( P < 0.001). Palmitate uptake, unaffected by insulin alone, was inhibited by NNF in extensor digitorum longus, white gastrocnemius, and tibialis anterior muscles; average inhibition was from 13.9 ± 1.2 to 6.9 ± 1.4 μmol · g−1 · h−1( P = 0.02). Thus NNF impairs both fatty acid and glucose uptake by muscle by restricting flow to myocytes but, as shown previously, favors triglyceride hydrolysis and uptake into nearby connective tissue fat cells. The findings have implications for lipid partitioning in limb muscles between myocytes and attendant adipocytes.

Interaction of a selective serotonin reuptake inhibitor with insulin in the control of hepatic glucose uptake in conscious dogs

“…Finally, there may be an indirect insulin-sensitizing effect of 5-HT at the liver. For example, much of the effect of 5-HT on muscle glucose uptake appears to be due to its ability to alter blood flow (3,31). Intraportal 5-HT infusion stimulated hepatic artery flow (22), but in the current studies there was no evidence for a fluvoxamineinduced alteration in hepatic blood flow in either the presence or absence of hyperinsulinemia.…”

Portal Serotonin Infusion and Glucose Disposal in Conscious Dogs

“…In addition, 5-HT has been shown to be a type B vasoconstrictor in skeletal muscle. Type B vasoconstrictors cause the channeling of blood away from the vessels that supply oxygen and nutrients to skeletal muscle ("nutritive flow") and into other vessels (those that supply connective tissue and associated adipocytes, creating "nonnutritive flow"), thus reducing muscle and hindlimb nutrient uptake (28,31). In this regard, the circulating concentrations of 5-HT achieved during P4 were higher than those that we have observed in four conscious dogs after intragastric glucose administration (peak value 1.8 Ϯ 0.2 g/ml; M.C.M.…”

Lipid metabolism and secretory function of porcine intramuscular adipocytes compared with subcutaneous and perirenal adipocytes

“…Last, it can be hypothesized that the specific function of IM adipocytes compared with that of SC and perirenal adipocytes may result, at least partly, from the competition between IM adipocytes and muscle fibers for nutrient uptake. Indeed, recent studies have underlined two vascular circuits for fatty acid supply in muscle, one (nutritive) supplying the myocytes, the other (nonnutritive) supplying the connective tissue and the closely associated IM adipocytes (8,9).…”