AN IN-VIVO STUDY OF THE EFFECTS OF ISCHEMIA ON UTERINE CONTRACTION, INTRACELLULAR PH AND METABOLITES IN THE RAT

1. There are no data concerning the functional or metabolic effects of hypoxia in, vivo in smooth muscle. We have therefore used P-31-NMR sp ectroscopy and intra-uterine pressure measurements to examine simultan eously, in vivo, the effect of ischaemia on uterine metabolites, intra cellular pH (pH(i)) and force. 2. A 1-2 cm portion of uterus from day 1 postpartum anaesthetized rats was exteriorized and an NMR surface co il placed on it. A balloon catheter in the uterine lumen recorded intr a-uterine pressure changes from the same area. Reversible occluders we re placed around the uterine artery. 3. Occlusion produced a decrease and then abolition of contractions, within 10 min. In four of five ani mals contraction was abolished within 2 min. Upon reperfusion force wa s rapidly restored (1 min), in all preparations. The mean level of for ce was significantly above control (pre-occlusion) 20-30 min after rep erfusion. 4. The NMR data showed a significant fall in [ATP] (28%) and [phosphocreatine] (34%) during occlusion. Inorganic phosphate doubled in concentration during this period. Metabolites recovered slowly upo n reperfusion, taking 20-30 min to return to preocclusion levels. 5. T he mean pH(i) fell from 7.32 to 7.00 upon occlusion and Was rapidly re versed upon reperfusion. The changes in pH(i) closely correlated With the changes in uterine force. Decreases of pH(i) of a similar magnitud e in, vitro have previously been shown to abolish contractions; thus i t is suggested that during ischaemia in vivo the depression of contrac tion is caused by the large fall in pH(i).