Developmental pattern of TRH-degrading activity and TRH content in rat pancreas

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Abstract
TRH, like several other neuropeptides, has been detected in the gastrointestinal tract of adult rats. More recently, elevated concentrations of TRH were found in the neonatal rat pancreas. This study was undertaken to evaluate pancreatic TRH degrading activity (TRH-DA) in infant rats from birth until adult life. Pancreatic TRH of age-matched rats was also measured by radioimmunoassay. TRH-DA was present in normal adult rat pancreas; through absent at birth and in the early postnatal period up to day 7, this activity was detected during the remainder of the developmental period. TRH content (pg .+-. stadard error of the mean per pancreas) was 1139 .+-. 88 on day 1, reached a peak value of 7360 .+-. 758 at day 2 and then decreased steadily to adult level. TRH-DA is present at birth in hypothalamus and liver but not in plasma. The developmental patterns of TRH-DA in plasma and in pancreas were parallel and seem to be thyroid hormone dependent. The absence of TRH-DA in the neonatal pancreas may also be related to the high TRH concentrations detected in this organ during the neonatal period.