Arbaprostil

The purpose of the present study was to investigate the relationship between the effects of 15(R)-15-methylprostaglandin E2 (arbaprostil) on gastric blood flow (GBF) and its protective effects on gastric lesions in rats. The GBF of anesthetized rats was measured by two different methods: Total blood flow into the stomach (total GBF) was determined by means of an ultrasonic pulsed Doppler flow meter; and gastric mucosal blood flow (mucosal GBF) was measured by nonradioactive microspheres. Systemic blood pressure (SBP), heart rate (HR) and gastric vascular resistance (GVR) were recorded simultaneously. Arbaprostil (10-100 micrograms/kg) given i.v. did not affect resting total or mucosal GBF even though it decreased SBP and GVR. Significant improvement of the total and mucosal GBF decreased by indomethacin pretreatment (10 mg/kg, i.v.) was observed by administration of arbaprostil (10-100 micrograms/kg, i.v.) in a dose-dependent manner. Furthermore, i.v.-administration of this agent, in the same dose-range, prevented the formation of gastric lesions induced by indomethacin. The present result suggests that mitigation for the ischemic state of the gastric mucosa may be one of the important mechanisms for the prophylactic and curative effect of arbaprostil on gastric lesions induced by indomethacin.

Gastric acid antisecretory activities of 15(R)-15-methylprostaglandin E2 (arbaprostil) preincubated or not preincubated with 0.9% physiological saline, the pH of which was precisely adjusted to less than 4.30, were examined in pylorus-ligated rats, and compared with those of 15(S)-15-methylprostaglandin E2 (15(S), epimer of arbaprostil). 15(S), unlike arbaprostil without preincubation, when s.c.-administered to rats significantly inhibited gastric acid secretion in a dose-dependent manner (30-300 micrograms/kg). However, arbaprostil preincubated at 37 degrees C for 30 min with 0.9% saline, at pHs of 4.30, 2.75 and 1.20, respectively, showed the following order of pH-dependent antisecretory activities: 1.20 greater than 2.75 greater than 4.30. An increase in 15(S) formation from arbaprostil in a pH-dependent manner was also observed by radioisotopic experiments under the same incubation conditions using [3H]-labeled arbaprostil. The present result suggests that the gastric antisecretory effect of arbaprostil can be mainly explained in terms of the formation of 15(S) after oral administration.