Effects of octopamine, chlordimeform, and demethylchlordimeform on amine-controlled tick salivary glands isolated from feeding Amblyomma americanum (L.)

The amine-controlled salivary glands of feeding female Amblyomma americanum (L.) ticks were isolated in saline and exposed to dopamine, octopamine, chlordimeform, and demethylchlordimeform. Octopamine stimulated a faster secretory rate than the demethylchlordimeform and dopamine prestimulation was not required. Octopamine was much less potent than dopamine as a stimulant. Chlordimeform (10^-5 M) stimulated little or no secretion following dopamine incubation but it subsequently antagonized the dopamine-stimulated (10^-5 M) response even though the chlordimeform had been removed. It (10^-5 M) did not enhance or antagonize and established maximal dopamine-stimulated response, nor did it significantly alter a near threshold dopamine-stimulated rate. Demethylchlordimeform stimulated secretion at rates 24 to 21% of those for dopamine (10^-7 M) but at concentrations 100- to 10,000-fold that of dopamine, and its action was expressed only after the glands had been prestimulated by dopamine. In the same experiments, the millimolar concentration significantly antagonized dopamine (10^-7 M)-stimulated secretion, but a 10 μM dose had much less of an effect. Gland preincubation with the formamidines was required before the addition of dopamine for antagonism of secretion to occur. Because these formamidines did not enhance dopamine-stimulated secretion or have potent intrinsic effects, it is unlikely that they inhibited gland monoamine oxidase. In conclusion, the relatively high threshold octopamine concentration and the lack of a potent effect by the formamidines show that octopamine receptors are not present in the gland. The formamidines can affect the secretory rate and therefore under certain physiological conditions could alter salivary gland functioning in the feeding tick.