Effects of moderate hyperthyroidism and time relative to feeding on tissue responsiveness to insulin in sheep.
The effects of moderate hyperthyroidism and time relative to feeding on tissue responsiveness to insulin were determined in four sheep using a hyperinsulinemic euglycemic clamp procedure, because thyroid hormones have glucoregulatory function in ruminants and non-ruminant animals. The sheep were fed alfalfa hay cubes and corn-based concentrates. They were intravenously injected in turn with saline (control treatment) and then with triiodothyronine (1.5 nmol d(-1); T3 treatment) once daily for 23 days for each treatment. The glucose clamp procedure was performed at four different times relative to feeding (before, during and after feeding) in both treatments. Insulin was intravenously infused at a constant rate of 6.0 mU (kgxmin)(-1) for 2 h and a glucose solution was infused to maintain euglycemia. Plasma T3 concentrations were higher (P=0.0001) for the T3 treatment than for the control treatment (4.0 and 1.3 nmol l(-1), respectively). For the glucose clamp procedure, glucose infusion rates were greater (P=0.0001) for the T3 treatment than for the control treatment, and were greater (P<0.05) during feeding than before feeding and after the end of feeding, but no interaction was detected. In conclusion, tissue responsiveness to insulin in sheep was independently enhanced by moderate hyperthyroidism induced by intravenous T3 injection and feeding.
Department of Agro-bioscience, Faculty of Agriculture, Iwate University, Morioka 020-8550, Japan. sano@iwate-u.ac.jp
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Sano
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Takebayashi
D000821:Animal Feed; D000818:Animals; D015309:Glucose Clamp Technique; D006980:Hyperthyroidism / Q000139:chemically induced / Q000378:metabolism*; D007328:Insulin / Q000097:blood / Q000737:chemistry; D007333:Insulin Resistance; D008657:Metabolic Clearance Rate; D012756:Sheep / Q000378:metabolism*; D014284:Triiodothyronine / Q000494:pharmacology
D007328:Insulin; D014284:Triiodothyronine