Effect of Restraint Stress on Plasma PTH Concentration and Its Molecular Targets Expressions in Wistar Rats

There are limited numbers of experimental studies related to the potential role of parathormone/parathyroid hormone (PTH) in response to psychological stress. In the current study, we aimed to cross-examine, for the first time, changes in PTH plasma concentration and the expression of its molecular targets mediated by restraint stress in rats.

Male Wistar rats (n = 42) were separated into control and stressed groups. They were further divided into two groups that received chronic restraint stress (CRS) for 7 and 28 consecutive days (n = 7 for each group). Elevated plus maze and tail suspension test were used to determine the anxiety- and depressive-like behaviors of a different set of rats including stress and control groups (n = 7 for each group). The plasma levels of adrenocorticotropic hormone (ACTH), corticosterone, and intact parathormone (iPTH) were measured by enzyme-linked immunosorbent assay (ELISA). In addition, alterations in the expressions of glucocorticoid receptor (GR), calcium sensing receptor (CaSR), and parathormone receptor (PTHR1) of kidney and total thyroid gland tissues were estimated by Western Blotting.

There was no significant difference in the plasma level of iPTH while significant increases in the levels of ACTH and corticosterone were noted in the stressed-animals at day 7 and 21 (P = 0.010 and P = 0.016, respectively) of restraint stress. However, we found a negative correlation between iPTH and corticosterone levels in acute restraint stress (r = 0.771, P = 0.002). In addition, the expression of PTHR1 significantly decreased in the kidney at day 7 (P = 0.001) and in the thyroid gland at day 28 (P = 0.05) in response to CRS.

To sum up, CRS has a significant effect on the expression of parathormone receptor rather than the iPTH concentration. The present results add a new dimension to stress research through the negative effect of chronic stress on the PTH signaling pathway.