Serum levels of TSH and thyroid hormones after TRH adminitration in the reindeer

Abstract

(p < 0.01) in TSH was observed 30 min after TRH injection. In winter the response to TRH was slow (38 %) and TSH concentrations re­ mained at low levels. In spring the basal levels of TSH seemed to be higher (p < 0.05) and the repsonse to TRH was greater than during other seasons. In control animals the concentrations of TSH remained at the basal level during all experiments. The highest basal level of T3 was detected in winter and the lowest level in sum­ mer. In response to TRH the peak serum T3 concetrations were detected in summer at 60 min and in spring at 120 min. In autumn du­ ring the rutting period the rise of 139 % in T3 levels was observed after 120 min from TRH injection. After the rut the highest levels were found at 90 min after injection. The lowest ba­ sal levels of T4 were detected in winter and the highest in spring. The highest rise (19.4 % at 30 minutes) after TRH injection was found in win­ ter. In summer the peak levels of T4 occurred 90 min after TRH injection and at 120 min du­ ring other seasons. Conclusions: The rutting period appeared to sti­ mulate the secretion of TSH and thyroid hor­ mones. The response of TSH to TRH is most pronounced in spring. In summer basal levels of T3 are at the lowest and the response to TRH is weaker than during other seasons. The effect of TRH on the T4 levels is highest in winter.