5-Hydroxytryptamine stimulates fluid secretion in locust malpighian tubules independently of cAMP.
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.
D000818:Animals; D001826:Body Fluids / Q000502:physiology; D002742:Chlorphenamidine / Q000494:pharmacology; D002988:Cloaca / Q000378:metabolism*; D000242:Cyclic AMP / Q000502:physiology*; D004298:Dopamine / Q000494:pharmacology; D006110:Grasshoppers / Q000502:physiology*; D008317:Malpighian Tubules / Q000187:drug effects / Q000378:metabolism*; D009655:Octopamine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology*
D009655:Octopamine; D012701:Serotonin; D000242:Cyclic AMP; D002742:Chlorphenamidine; D004298:Dopamine; D010646:Phentolamine