PULSATILE THYROTROPIN AND PROLACTIN SECRETION IN A MIXED THYROTROPIN-SECRETING AND PROLACTIN-SECRETING PITUITARY-ADENOMA

The circadian and pulsatile thyrotropin (TSH) and prolactin (PRL) release was investigated in a patient with slight hyperthyroidism due to a mixed TSH- and PRL-secreting pituitary adenoma. Blood was withdrawn every 10 min for 24 h (before and after medical treatment); purse characteristics were analyzed by Desade and Cluster programs (values as mean+/-SD). The inappropriately high mean 24-h TSH concentration of 3.55+/-0.31 mU/l was associated with a higher mean 24-h TSH pulse amplitude but unaltered mean 24-h TSH pulse frequency relative to healthy controls. The nocturnal TSH surge (absolute surge 0.5 mU/l, relative surge 16%) was low, related to a loss of the usual nocturnal increase of TSH pulse amplitude and TSH purse frequency. Chronic treatment with octreotide resulted in a modest clinical and biochemical improvement of the hyperthyroid state; addition of bromocriptine at a later stage had no further beneficial effect. At the end of the follow-up period the mean 24-h TSH paradoxically had increased to 5.33+/-0.81 mU/l. The nocturnal TSH surge also increased (absolute surge 1.9 mU/l, relative surge 42%), but circadian changes in TSH pulsatility remained absent. In the untreated period the increased mean 24-h PRL concentration of 234+/-24 mu g/l was associated with an increased mean 24-h PRL amplitude, whereas the 24-h PRL pulse frequency (N=4) was lower relative to controls. No circadian PRL rhythm was present. After octreotide and bromocriptine treatment the mean 24-h PRL concentration and mean 24-h PRL pulse amplitude were unchanged, but a clear nocturnal increase of PRL now was observed. Analysis of the temporal coupling between TSH and PRL release by bivariate autoregressive modeling revealed significant cross-correlations in all three periods investigated (coefficients in the range 0.34-0.76, median 0.52; p<0.01) between TSH and PRL concentrations with a lag time of 10-20 min. We conclude that pulsatile TSH and PRL release in this mixed TSH- and PRL-secreting pituitary adenoma was autonomous in nature. The observed dampening of the nocturnal increase of TSH and PRL is putatively related to a lack of TRH receptors in these tumors. The observed co-secretion of TSH and PRL suggests synthesis of both hormones by the same cell.