MICROINJECTION OF THYROTROPIN-RELEASING-HORMONE IN THE PARAVENTRICULAR NUCLEUS OF THE HYPOTHALAMUS STIMULATES GASTRIC CONTRACTILITY

Changes in gastric contractility following microinjection of thyrotrop in-releasing hormone (TRH) into the paraventricular nucleus of the hyp othalamus (PVN) were examined in fasted, urethane-anesthetized rats. G astric contractility was measured with extraluminal force transducers and analysed by computer. Unilateral and bilateral PVN microinjections of TRH (0.5 and 1.0 mu g) significantly increased the force index of gastric contractions from 0 to 60 min postinjection, when compared wit h animals microinjected with 0.1 mu g TRH, 0.1% BSA or TRH (0.5 and 1. 0 mu g TRH) in sites adjacent to the PVN. The gastric force index was also significantly elevated from 61 to 120 min postinjection in rats r eceiving bilateral PVN microinjections of TRH (0.5 and 1.0 mu g) Peak gastric responses occurred within 10-20 min postinjection and represen ted an approximately eight-fold increase over basal values. In the rem aining groups, the force index was not significantly altered from prei njection values. The excitatory action of TRH (1.0 mu g) on gastric co ntractility was completely abolished by subdiaphragmatic vagotomy. The se results suggest that TRH acts within the PVN to stimulate gastric c ontractility via vagal-dependent pathways.