Effect of caloric restriction and dietary composition of serum T3 and reverse T3 in man.

To evaluate the effect of caloric restriction and dietary composition on circulating T3 and rT3 obese subjects were studied after 7-18 days of total fasting and while on randomized hypocaloric diets (800 kcal) in which carbohydrate content was varied to provide from 0 to 100% calories. As anticipated, total fasting resulted in a 53% reduction in serum T3 in association with reciprocal 58% increase in rT3. Subjects receiving the no-carbohydrate hypocaloric diets for two weeks demonstrated a similar 47% decline in serum T3 but there was no significant change in rT3 with time. In contrast, the same subjects receiving isocaloric diets containing at least 50 g of carbohydrate showed no significant changes in either T3 or rT3 concentration. The decline in serum T3 during the no-carbohydrate diet correlated significantly with blood glucose and ketones but there was no correlation with insulin or glucagon. We conclude that dietary carbohydrate is an important regulatory factor in T3 production in man. In contrast, rT3 concentration is not significantly affected by changes in dietary carbohydrate. Our data suggest that the rise in serum rT3 during starvation may be related to more severe caloric restriction than that caused by the 800 kcal diet.

Hyperinsulinemic hypoglycemia associated with a neurofibrosarcoma.

A patient with a posterior mediastinal malignant neurofibrosarcoma and recurrent episodes of severe hypoglycemia was demonstrated to have basal hyperinsulinemia on repeated study. Despite hypoglycemia, there was no glucagon response to aminogenic stimulation. No immunoreactive insulin was detected on extraction of the tumor and no secretory granules of beta type were seen on electron microscopic examination of tumor tissue. Following tumor removal, plasma glucose and insulin levels returned to normal. Alpha cell function improved. These findings suggest stimulation of pancreatic beta cell secretion and possible inhibition of alpha cell response by an extrapancreatic tumor.