DIFFERENCES IN THE NYCTOHEMERAL SECRETION OF TSH AND PRL IN HEALTHY EUTHYROID MEN

The circadian rhythm of TSH, PRL and cortisol was studied in 21 health y euthyroid men in a normal sleep/wake cycle. Higher nyctohemeral (22. 00 h till 6.00 h) levels of TSH as compared to diurnal (8.00 h till 22 .00 h) levels were observed in 14 out of 21 men (Group A). In the rema ining 7 volunteers the nyctohemeral and diurnal TSH-levels (Group B) w ere the same. In Group A, the nyctohemeral PRL-surge was also higher t han in Group B (p < 0.01). The nyctohemeral area under the curve (AUC) of both TSH and PRL were significantly higher in Group A than in Grou p B (p < 0.05 and p < 0.001 respectively). The mean diurnal concentrat ions of TSH and PRL were, however, similar in both groups. Therefore, an impairment of the nyctohemeral TSH-surge can occur in healthy men u sually combined with a reduced nyctohemeral PRL-surge. An impairment o f nyctohemeral TSH-surge is thus not confined to patients with thyroid diseases.