Decreased neuropeptide Y (NPY) expression in the infundibular nucleus of patients with nonthyroidal illness.

In patients with a variety of illnesses, serum concentrations of T3 decrease without giving rise to elevated serum levels of TSH, a phenomenon known as the sick euthyroid syndrome or nonthyroidal illness (NTI). Our previous studies in postmortem brain material showed decreased thyrotropin-releasing hormone (TRH) messenger RNA (mRNA) in the paraventricular nucleus (PVN) of patients with NTI, suggesting a role for TRH cells in the persistence of low TSH levels in NTI. In the present study, we hypothesized that changes in neuropeptide Y (NPY) input from the infundibular nucleus (IFN) to TRH cells in the PVN might be a determinant of decreased TRH expression in NTI.