Age-Related Variations in Jejunum and Distal Colon Contractile Response to Thyrotropin-Releasing Hormone in vitro

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Abstract
The effects of thyrotropin-releasing hormone (TRH) on the contractile activity of the proximal jejunum and distal colon of 3-, 7-, 14-, 21-, 28-, 50-day-old and adult male Sprague-Dawley rats were examined. Longitudinal segments were mounted in force displacement transducers and bathed in oxygenated, buffered Krebs’ solution. In the proximal jejunum TRH 10––6 M produced a tetrodotoxin (TTX)-sensitive tension increase in 3- to 14-day-old rats and a TTX-resistant biphasic response in older rats. TRH 10––6M produced a transient tension in the distal colon of rats ≤ 21 days old. Incubation with TRH 10––6M for 30min increased responsiveness to acetylcholine 10––7M in approximately 50% of tissues studied. Direct and indirect effects of TRH are developmentally determined.