Endocrine Abstracts

Introduction: The role of the pineal gland and its hormone, melatonin, in the regulation of hypothalamo-adenohypophysial system activity is well known. At the same time, studies of the circadian rhythm of melatonin secretion in patients with pituitary adenomas are few in number, because the evaluation of pineal activity is not generally included in the clinical investigation of patients with pituitary tumors.

Aim: The present study analyzed the circadian diurnal melatonin profile, in patients with GH/prolactin (PRL) secretion adenomas.

Subjects and methods: Under investigation there were 69 patients aged 18–75 years with pituitary tumors: 52 acromegaly (ACRO) (female 32/male 20); 17 prolactinoma (PROL) (female 14/male 3), by comparing the results with those seen in 10 healthy controls. All the patients had active disease and were off treatment; none had overt hypopituitarism. Blood samples for GH and PRL were taken in fasting state. 6-Sulfatoxymelatonin (MT), the main melatonin metabolite, was determined by fluorometric assay by C. Druex in two separated urine portions: in the daytime (MTd) and nighttime (MTn) in the spring/autumn period. Data are given as M±S.D., Me, [Mim – Max].

Results: Abnormally high serum levels of MT during the period of maximum light and abnormally low increases during the night were seen in 31/52 ACRO (GH-23.6±24.1, Me=14.0 [3.1-144.9] ng/l) and 12/17 PROL (PRL - 248.5±551.4, Me=61.2 [2.35 - 3857.9] ng/l) patients. Moreover, mean levels of MT were significantly lower in patients than in controls. In ACRO patients total diurnal MT (85.08±62.65; Me=70.3 [9.5–324.6] nmol/24 h) and MTd levels (43.04±31.25; Me=33.65 [6.3–155.4] nmol/24 h) were significantly higher comparing patients with PROL: MT total - 49.58±20.71; Me=53.2 [17.8–103.2] nmol/24 h, P=0.0001; MTd – 30.0±19.24; Me=31.24 [5.4–82.5] nmol/24 h, P=0.03. It was found that in ACRO patients with daily rhythm inversion of melatonin excretion (MT-Ratio night/day < 1), MTn level was also significantly higher in comparison with PROL: 28.4±18.3, Me=25.4 [3.2 – 77.8] nmol/24 h; 16.4±5.8, Me=16.7 [5.9 – 26.6] nmol/24 h, respectively; P=0.0003.

Conclusion: This study demonstrates the existence of an altered pineal function in patients with pituitary tumors. Further studies will be required to establish the pathogenetic and prognostic significance of pineal disorders in neoplastic disease of the pituitary gland.