Diurnal secretion profiles of growth hormone, thyrotrophin and prolactin in Parkinson's disease

Recently, a massive loss of both hypocretin and melanin‐concentrating hormone (MCH) neurones was found in the hypothalamus of Parkinson’s disease (PD) patients. Because both hypocretin and MCH play a key role in the regulation of sleep, energy homeostasis and autonomic function, partly by modulation of the somatotrophic, thyrotrophic and lactotrophic axes, neuroendocrine dysregulation may contribute to some of the non‐motor features of PD. In eight de novo, medication‐free PD patients and eight age‐, sex‐ and body mass index‐matched controls, we measured serum levels of growth hormone (GH), thyroid‐stimulating hormone (TSH) and prolactin every 10 min for 24 h. Auto‐deconvolution, cosinor and approximate entropy analysis were applied to quantify GH, TSH and prolactin secretion rates, diurnal rhythmicity, as well as regularity of hormone release. Sleep was polygraphically‐recorded throughout the night. Total 24‐h secretion of GH (191 ± 31 versus 130 ± 39 mU/l/24 h), TSH (38 ± 9 versus 36 ± 2 mU/l/24 h) and prolactin (102 ± 14 versus 116 ± 17 μg/l/24 h), as well as their diurnal rhythmicity and regularity of release, were not significantly different between PD patients and controls (all P ≥ 0.12). Fasting levels of insulin‐like growth factor‐1 were also unaltered in PD patients. However, free thyroxine (T₄) levels were significantly higher in PD patients compared to controls (16.19 ± 0.80 versus 13.88 ± 0.40 pmol/l; P = 0.031). In PD patients, prolactin levels were related to disease duration (r = 0.76, P = 0.028), whereas both GH (r = ?0.91, P = 0.002) and free T₄ (r = ?0.71, P = 0.050) levels correlated inversely with body fat content. Apart from a mild increase in free T₄ levels, we found no indications for altered somatotrophic, thyrotrophic and lactotrophic axes activity in early‐stage PD patients.