Evidence that intraluminal pressure affects high potassium- and serotonin-induced contractions differently in the bovine middle cerebral artery: an in vitro study.

The effects of changing intraluminal pressure on contractions induced by 70 mM potassium (K+) and 10(-7), 10(-6), and 10(-5) M serotonin (5-HT) were studied in vitro in bovine middle cerebral arteries. Changes in vessel outside diameter in whole-mounted cylindrical sections of artery were detected with a photoelectric infrared device. High K+-or 5-HT (10(-5)M)-induced contractions peaked at 25 mm Hg and were significantly correlated with increasing intraluminal pressure between 25 and 175 mm Hg. Contractions induced with lower concentrations of 5-HT (10(-6), 10(-7) M), norepinephrine, and histamine peaked at 75 mm Hg but were not significantly correlated with rising pressure. Phentolamine (2 X 10(-6) M) added to the extraluminal bath had negligible influence on pressure's ability to affect K+- and 5-HT-induced contractions differently. Reducing bath temperature to 27 degrees C reduced the K+ response at each pressure, but similar temperature changes had little affect on the 5-HT-induced contractions. The K+ response became less sensitive to increasing pressure at low temperatures. Nifedipine (10(-7) M) almost totally eliminated K+-induced contractions, while significantly reducing the responses to all concentrations of 5-HT. The 5-HT responses appeared more sensitive to increasing intraluminal pressure in the presence of nifedipine. Maximum Ca++-induced contractions in the presence of 10(-5) M 5-HT and high K+ occurred at 25 mm Hg, while Ca++-induced contractions and Ca++-induced contractions in the presence of 10(-7) 5-HT or K+ plus 5-HT were maximum at 75 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)