Circadian rhythm of TSH in adult onset non-insulin dependent (type II) diabetics with altered thyroid state.

Twenty adult onset non-insulin dependent (Type II) diabetic patients and twenty non-diabetic subjects matched for sex, age, height and weight were studied. The diabetes was controlled by diet only in 10 patients and by oral hypoglycemic agents in 10. All patients were diurnally active and rested at night. Blood was sampled at 4-hour intervals over a 24-hour span (6 samples). TSH, total T3 and total T4 were determined by radioimmunoassay. The circadian rhythm in TSH was statistically significant by cosinor analysis and was comparable in all rhythm parameters in diabetics and non-diabetics. The rhythms of total T3 and T4 also seem to persist with comparable timing although the small number of subjects did not allow rhythm detection at the 5 per cent level in all groups. The circadian mean of the total T3 plasma concentration in the diabetics, however, was statistically significantly lower than the usual range of this laboratory and the total T4 was elevated but within the usual range. The changes in total T3 and T4 were most pronounced in the patients on oral hypoglycemic agents. This study indicates persistence of a circadian rhythm in TSH (and presumably also in the plasma concentrations of total T3 and T4) in non-insulin dependent diabetic patients in spite of a lowered circadian mean concentration of total T3 and a slightly but statistically significantly higher total T4 than in the matched non-diabetic subjects. The altered thyroidal state in the diabetic patients thus does not interfere with the circadian periodic secretion of TSH.