Time of Day-Dependent Effects of Thyroliberin and Thyrotropin on Thymocyte Proliferation in Rats

Abstract

Our earlier studies have shown that thyroliberin (TRH) as well as thyrotropin (TSH) enhanced thymus cell proliferation. The aim of the present study was to investigate whether the effects of TRH and TSH on thymocyte proliferation depend on time of day. A single subcutaneous injection of TRH (25 μg/animal) or TSH (3 IU/animal) was made at 9:00 h (1 h after light onset) or at 18:00 h (10 h after light onset) in 3-month-old male Wistar rats. The animals were killed 24 h later. The proliferation of thymocytes was assessed by incorporation of bromodeoxyuridine into cell nuclei. Thymocyte proliferation was significantly increased by TSH administration at 9:00 h, whereas treatment given at 18:00 h was ineffective. TRH enhanced the proliferation when injected at 9:00 h, but had an inhibitory effect when administered at 18:00 h. These data indicate that the effects of TRH and TSH on thymocyte proliferation are dependent on time of day.

Integrative study of hypothalamus–pituitary–thyroid–immune system interaction: thyroid hormone-mediated modulation of lymphocyte activity through the protein kinase C signaling pathway

“…With respect to TRH, it was suggested that this hormone exerts both direct and indirect effects on the immune system. Acute and chronic administration of TRH enhances the proliferation of splenic and thymic lymphocytes in rats (Winczyk & Pawlikowski 2000). Finally, TRH administration in humans led to increased secretion of IL-2 into the blood .…”

Hypothalamic neurohormones and immune responses

“…In fact, it has been reported that TRH promotes thymic reconstitution in mice with anterior hypothalamic area lesions (Lesnikov et al, 1991). According with these data, it was also reported that TRH enhances the in vitro plaque-forming cell response (Kruger et al, 1989), antagonizes the dexometasone-induced thymocyte and splenocyte suppression (Winczyk and Pawlikowski, 2000) and administration in humans led to increased secretion of IL-2 into the blood (Komorowski et al, 1993). …”

“…Acute and chronic administration of TRH enhances the proliferation of splenic and thymic lymphocytes in rats (Pawlikowski et al, 1992; Raiden et al, 1995; Winczyk and Pawlikowski, 2000). In fact, it has been reported that TRH promotes thymic reconstitution in mice with anterior hypothalamic area lesions (Lesnikov et al, 1991).…”