The Journal of International Medical Research 1991; 19: 389 - 394

Thyroid Function and Release of Thyroid-stimulating Hormone and Prolactin from the Pituitary in Human Obesity R. Scaglkme', M.R. Averna', M.A. Dichiara', C.M. Barbagallo', G. Mazzola', G. Montalto2, G. Licata' and A. Notarbartolo! 'Department ofMedical Pathology, Institute ofClinical Medicine, University ofPalermo, Palermo, Italy; 2Department ofMedical Pathology, Institute ofInternal and Geriatric Medicine, University of Palermo, Palermo, Italy

Thyroid function, basal serum thyroid-stimulating hormone (TSH) and prolactin concentrations, and the effects of 200 ug TSH-releasing hormone (TRH) given intravenously on TSH (ilTSH) and prolactin (Aprolactln) were investigated in 25 euthyroid obese subjects and 20 lean controls. No significant differences in serum thyroid hormone concentrations, glucose metabolism parameters, or basal TSH and prolactin concentrations were detected between groups, but a significant (P < 0.01) increase in ilTSH and a significant (P < 0.01) decrease in Aprelactln were observed in obese subjects. No significant differences in basal TSH and prolactin were observed in obese men and women compared with corresponding lean controls, but ilprolactin decreased significantly (P < 0.01) in obese men and women compared with lean controls and TSH increased significantly (P < 0.01) in obese men and women. No correlation was found between ilTSH or ilprolactin and body mass index. The study suggests that hyper-responsiveness of TSH and hyporesponsiveness of prolactin to TRH in obese subjects can be related to changes in the central serotoninergic system. KEY WORDS: Thyroid-stimulating hormone; prolactin; thyroid-stimulating hormone-releasing hormone; obesity; serotoninergic system.

INTRODUCTION Received for publication 3 July 1991; accepted 8 July 1991. Address for correspondence: Dr R. Scaglione, Via Lombardia 9, 901444 Palermo, Italy. © Copyright 1991 by Cambridge Medical Publications Ltd

number of endocrinological changes have been well documented in obese subjects, including glucose intolerance and hyperinsulinaemia, increased cortisol

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turnover and a reduction in fasting growth hormone concentrations and its response to insulin-induced hypoglycaernia.!-' No unequivocal data, however, have been reported on thyroid-stimulating hormone (TSH) and prolactin release from the pituitary in obesity. 2 - 6 Donders et al,' found a disparity in the responsiveness of TSH and prolactin to TSH-releasing hormone (TRH) in obese women, with hyper-responsiveness ofTSH and hyporesponsiveness of prolactin. This phenomenon was related to a variation in central serotoninergic activity which has been implicated in the pathogenesis of obesity.' There have been few studies carried out to evaluate whether or not the hypothalamic - pituitary abnormalities observed in obese women are also present in obese men. For these reasons thyroid function and basal and TRH-stimulated release of TSH and prolactin were studied in both female and male obese, euthyroid subjects and compared to responses in lean control subjects.

PATIENTS AND METHODS

Patients A total of 25 obese, but otherwise healthy subjects (15 females, 10 males; mean age 30.75 ± 4.06 years, range 25 - 35 years), with a body mass index (BMI) of more than 30 were studied. A control group consisted of 20 euthyroid and lean (BMI < 25) subjects (l0 females, 10males; mean age 32.15 ± 5.06 years, range 27 - 32 years). None of the subjects enrolled suffered from thyroid disease or diabetes, or used oral contraceptives or other drugs. No dietary advice was given before carrying out the study. Informed consent was obtained from all subjects.

Relefact" is a registered tradename of Hoechst, FRG.

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Clinical evaluations In all the subjects the following parameters were evaluated: serum total thyroxine and free thyroxine, total and free triiodothyronine by radioimmunoassay;" serum TSH and prolactin before and after the TRH test by immunoradiometric assay;" fasting blood glucose measured enzymatically; 10 glycosylated haemoglobin (haemoglobin Ale) by ion exchange chromatography; 11 and serum fructosamine by colorimetry .12 Thyroid scintigraphy was also performed. All tests were started at 08.00 h in fasted subjects who were resting in bed. Blood samples for the determination of TSH and prolactin were collected 30 and 0 min before, and 10, 20, 30, 60 and 120 min after intravenous bolus administration of 200 ug synthetic TRH (Relefact"), Changes in TSH and prolactin concentrations in response to TRH were given in relation to baseline and were the mean maximum increments. Statistical analysis All the data are expressed as means (± SD). Statistical analysis was performed using Student's t-test and Spearman's rank correlation test. RESULTS

In comparison with the control, non-obese subjects BMI was significantly (P