Microinjection of thyrotropin-releasing hormone in the paraventricular nucleus of the hypothalamus stimulates gastric contractility

Changes in gastric contractility following microinjection of thyrotropin-releasing hormone (TRH) into the paraventricular nucleus of the hypothalamus (PVN) were examined in fasted, urethane-anesthetized rats. Gastric contractility was measured with extraluminal force transducers and analysed by computer. Unilateral and bilateral PVN microinjections of TRH (0.5 and 1.0 μg) significantly increased the force index of gastric contractions from 0 to 60 min postinjection, when compared with animals microinjected with 0.1 μg TRH, 0.1% BSA or TRH (0.5 and 1.0 μg TRH) in sites adjacent to the PVN. The gastric force index was also significantly elevated from 61 to 120 min postinjection in rats receiving bilateral PVN microinjections of TRH (0.5 and 1.0 μg). Peak gastric responses occurred within 10–20 min postinjection and represented an approximately eight-fold increase over basal values. In the remaining groups, the force index was not significantly altered from preinjection values. The excitatory action of TRH (1.0 μg) on gastric contractility was completely abolished by subdiaphragmatic vagotomy. These results suggest that TRH acts within the PVN to stimulate gastric contractility via vagal-dependent pathways.