Actions of Aminophylline on the Blood Sugar, Serum Insulin and Serum free Fatty Acid Responses to Glucose in Hyperthyroid Dogs

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Abstract
The effects of aminophylline-preinfusion on the altered BS, serum IRI and serum FFA responses to glucose in anesthetized, recent hyperthyroid dogs were studied. Hyperthyroidism was induced by T4 administration. Aminophylline administration (priming-dose and continuous infusion) immediately preceded glucose administration (priming-dose followed by continuous infusion). Normal and hyperthyroid controls, which did not receive aminophylline, were given just glucose. Hyperthyroidism failed to affect the basal levels of BS and serum IRI of these dogs, but raised those of serum FFA. Aminophylline-preinfusion for 1 hour did not further modify these variables. Recent hyperthyroidism caused moderate intolerance to infused glucose, which was reverted by aminophylline-preinfusion. The early insulin response to glucose, missing in the hyperthyroid dogs, was stimulated by aminophylline; the normal biphasic pattern of insulin secretion, however, was not restored. In the normal group, serum FFA were very low all over the glucose test. In the hyperthyroid one, serum FFA were intensely responsive to combined hyperglycemia and hyperinsulinemia and, then, slowly recovered; aminophylline-preinfusion depressed the early fall and moderately promoted the subsequent rebound of this variable. Results are discussed on the basis that whichever is the mechanism whereby recent hyperthyroidism impairs the insulin-secretory response to hyperglycemia, the impairment is greatly suppressed - and the BS profile is restored - by enhancing the body cells' cAMP level. BS blood sugar; IRI immunoreactive insulin; FFA free fatty acids; PBI protein-bound iodine; T4 thyroxine; GIT glucose infusion test. 1 This work, partly published in abstract form (VI Congreso Bolivariano de Endocrinologia, La Paz, Bolivia, November 1-5, 1977), was supported by the "Consejo Nacional de Investigaciones Científicas y Técnicas" (CONICET), Res. Grant No. 2304-h/76, and by Buenos Aires University, Argentina.