Comparison of the effect of TRH on plasma TSH level in young and adult rats.
Since it is known that TRH degrading system in plasma is inactive during suckling period in the rat, it was of interest to see whether this might prolong the effect of TRH on plasma TSH. Time course of plasma TSH after s. c. administration of 2 ng TRH g-1 was studied in 7, 48 and 120 day-old rats. The highest basal TSH level (448 +/- 72 microU ml-1) was found in 48 day-old males, while it was the lowest (82 +/- 22.8 microU ml-1) in 7 day-old animals. Time course was essentially the same in all three age groups. If the increase of plasma TSH was compared to the level of saline treated controls at the same time, 8.2 and 10.1 fold increase was found 10 and 30 min after TRH injection, respectively, in 7 day-old pups. However, the increase was only 2.3 and 3.4 fold in older animals at the same time intervals. The highest absolute level obtained during TRH stimulation was found in 48 day-old animals (1055 +/- 121.6 microU ml-1). These results show that the effect of TRH on plasma TSH was not prolonged in neonatal rats thus suggesting that extravascular TRH degradation may be of some importance in TSH regulation.
D000375:Aging; D000818:Animals; D000831:Animals, Newborn / Q000097:blood; D005260:Female; D008297:Male; D051381:Rats; D013972:Thyrotropin / Q000097:blood*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D013997:Time Factors
D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin