Article date: February 1984
By: H. Karaki, K. Murakami, H. Nakagawa, N. Urakawa in Volume 81, Issue 2, pages 387-392
Nitroglycerine induced biphasic relaxation in the rat aorta, previously contracted by noradrenaline; a rapid decrease in tension was followed by a gradual increase reaching a steady level below the control contractile tension. No initial transient relaxation was induced by nitroglycerine in high K‐stimulated muscle.
The initial transient relaxation, but not the sustained relaxation, was dependent on the concentration of external K; maximum relaxation was observed in the presence of 2.7 mm K solution and only a slight relaxation was observed in 0 mm or 10.8 mm K solution. The initial transient relaxation was also inhibited by ouabain or low Na solution.
On an appropriate increase in the concentration of external K, noradrenaline‐induced contraction was transiently relaxed. Previous application of nitroglycerine potentiated this K‐induced relaxation.
Pretreatment of the muscle with methylene blue, an inhibitor of guanylate cyclase, inhibited both the initial transient and the sustained relaxations induced by nitroglycerine, but not the K‐induced transient relaxation.
It is suggested that the nitroglycerine‐induced initial transient relaxation, but not the sustained relaxation, may be due to a stimulation of an electrogenic Na pump. Both relaxation phases may be mediated by cyclic GMP.
Nitroglycerine induced biphasic relaxation in the rat aorta, previously contracted by noradrenaline; a rapid decrease in tension was followed by a gradual increase reaching a steady level below the control contractile tension. No initial transient relaxation was induced by nitroglycerine in high K‐stimulated muscle.
The initial transient relaxation, but not the sustained relaxation, was dependent on the concentration of external K; maximum relaxation was observed in the presence of 2.7 mm K solution and only a slight relaxation was observed in 0 mm or 10.8 mm K solution. The initial transient relaxation was also inhibited by ouabain or low Na solution.
On an appropriate increase in the concentration of external K, noradrenaline‐induced contraction was transiently relaxed. Previous application of nitroglycerine potentiated this K‐induced relaxation.
Pretreatment of the muscle with methylene blue, an inhibitor of guanylate cyclase, inhibited both the initial transient and the sustained relaxations induced by nitroglycerine, but not the K‐induced transient relaxation.
It is suggested that the nitroglycerine‐induced initial transient relaxation, but not the sustained relaxation, may be due to a stimulation of an electrogenic Na pump. Both relaxation phases may be mediated by cyclic GMP.
DOI: 10.1111/j.1476-5381.1984.tb10090.x
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