Ion and Water Balance in the Ixodid Tick Dermacentor Andersoni

Abstract

1. An in vitro method is described for stimulating the salivary gland of Dermacentor andersoni to secrete fluid. In vitro glands require the presence of a catecholamine for salivation to occur. Natural haemolymph from salivating ticks does not trigger secretion suggesting that the tick does not produce a ‘salivation hormone’ analogous to the diuretic hormones of certain insects. 2. Piocarpine, glutamate and malate did not stimulate secretion in vitro. Isoproterenol and 5-hydroxytryptamine were relatively weak stimulants (threshold concentrations of approximately 10^-5 M and greater than 10^-4 M respectively). Adrenaline, noradrenaline and dopamine were highly effective stimulants, the threshold concentrations being no more than 10^-5 M. Adrenaline could also elicit a copious secretion in vivo at a final haemocoele concentration of about 2 x 10^-5 M. 3. We postulate that salivation occurs by means of a secretory rather than a filtration-resorption mechanism. Control of fluid secretion is probably neural rather than hormonal, the transmitter substance being a catecholaminergic substance.