Relationships between the circadian rhythms of TSH, prolactin and cortisol in surgically treated microprolactinoma patients

Abstract

Pharmacological doses of glucocorticoids inhibit TSH release both in vivo and in vitro and since the circadian rhythms of TSH and cortisol show a reciprocal relationship, the hypothesis has been advanced that changes in cortisol levels may be a primary determinant of circadian TSH changes. We have tested this hypothesis by studying the relationship between circadian cortisol and TSH rhythms in subjects before and during blockade with metyrapone. Seven patients were studied during their routine post-operative assessment following selective transethmoidal adenomectomy for microprolactinomas. PRL levels were restored to normal (less than 420 mU/l) in all patients by surgery (pre-op: 930-2752 mU/l, post-op: 33-376 mU/l) and the patients also had normal pituitary function in other respects. Blood was sampled hourly for 24 h before and on the third day of treatment with metyrapone (250 mg, 2 hourly). In order to compare circadian rhythms, hormonal data were subjected to cosinor analysis which involved fitting of the data with a cosine function using the method of least squares. The 6% cross reactivity of the cortisol antibody with 11-deoxycortisol was taken into account during the calculation of results. All subjects showed a normal cortisol rhythm which was strikingly blunted during metyrapone treatment. Group mean (+/- SD) TSH mesors, amplitudes and acrophases for control and metyrapone treated subjects were 1.5 +/- 0.26, 1.29 +/- 0.48; 0.46 +/- 0.26, 0.23 +/- 0.13 and -49 degrees +/- 9.8 degrees; -62 degrees +/- 2.7 degrees respectively.(ABSTRACT TRUNCATED AT 250 WORDS)