| 6151458 |
Morgan PJ, Mordue W: 5-Hydroxytryptamine stimulates fluid secretion in locust malpighian tubules independently of cAMP. Comp Biochem Physiol C. 1984;79(2):305-10.
5-Hydroxytryptamine (5-HT) stimulates fluid secretion by semi-isolated Malpighian tubules of Locusta in a dose-dependent manner. The threshold of stimulation is between 10 (-8) and 10 (-7) M 5-HT; maximal activation occurs at doses greater than 10 (-6) M. Relative to the activation induced by diuretic hormone (storage lobe extracts), 5-HT increases the rate of fluid secretion by only 65%. Phentolamine, the alpha-adrenergic blocker, failed to inhibit either DH or 5-HT stimulated secretion. Diuretic hormone raises the levels of intracellular of cAMP, and activates adenylate cyclase in plasma membrane preparations of Locusta Malpighian tubules. 5-HT (10 (-4) M) has no effect in either assay system. Thus 5-HT can stimulate fluid secretion independently of cAMP. A hypothetical model for hormone stimulated fluid secretion by Locusta Malpighian tubules, involving dual-receptor activation, is proposed. Other biogenic amines, including octopamine, adrenalin, dopamine, synephrine and the formamidine chlordimeform were tested for their ability to stimulate fluid secretion. Only dopamine showed a weakly stimulatory effect. |
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