Cyclical effects of triiodothyronine on blood-free fatty acid and glucose concentrations in warm-adapted and cold-adapted rats.
Effects of triiodothyronine (T3) (100 mug/100 g, sc) on blood-free fatty acid (FFA) and glucose concentrations were investigated in warm- and cold-adapted rats. Blood specimens were obtained from the tail locally anesthetized with lidocaine. In warm-adapted rats FFA rose 3 to 6 hr after administration of T3, but returned to the pre-injection level 12 hr later. Thereafter, blood FFA level showed a repeated cyclical rise and fall every 12 hr for up to 60 hr, while blood glucose level did not increase until 12 hr later and this level was maintained for up to 36 hr. After that time it also showed a repeated rise and fall every 12 hr for up to 60 hr. Both FFA and glucose levels returned to the initial values after 72 hr. Changes induced by T3 in blood levels of these metabolites were reciprocal. In cold-adapted rats the patterns of responses to T3 were essentially the same as those observed in warm-adapted ones, except that T3 provoked a simultaneous rise in blood glucose as well as FFA 6 hr after injection, although an extent of FFA increment was less than in warm-adapted rats. Reserpine pre-treatment caused a considerable reduction in the FFA mobilizing action of T3. The FFA and glucose mobilizing action of T3 was also observed at dosages of 25 and 6.25 mug/100 g, although to lesser extent. These results indicated for the first time the cyclical action of T3 on blood FFA and glucose concentrations, and a changed sensitivity to T3 in cold-adapted animals.
D000064:Acclimatization; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D003080:Cold Temperature; D004305:Dose-Response Relationship, Drug; D005230:Fatty Acids, Nonesterified / Q000097:blood*; D006358:Hot Temperature; D008297:Male; D010507:Periodicity; D051381:Rats; D012110:Reserpine / Q000494:pharmacology; D013268:Stimulation, Chemical; D014284:Triiodothyronine / Q000494:pharmacology*
D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D014284:Triiodothyronine; D012110:Reserpine