Secretory activity in salt glands of birds and turtles: stimulation via cyclic AMP

O2 consumption in tissue slices from the nasal salt gland of the duck and the lachrymal salt gland of Malaclemys is stimulated by methacholine, a stimulation that is inhibited by bumetanide and by ouabain. In addition, the calcium ionophore A23187 mimics the action of methacholine in stimulating this secretion-related O2 consumption in both glands, suggesting a second-messenger role for this ion in the cholinergic response. However, the adenylate cyclase activator, forskolin, and the cyclic AMP analogue, 8-cpt-cAMP, also stimulate ouabain-sensitive and bumetanide-sensitive O2 consumption in both the duck gland and the Malaclemys gland. It is suggested that the mechanism of salt secretion in the Malaclemys lachrymal gland conforms to that previously described for other extrarenal salt-secreting tissues in nonmammalian vertebrates and, as in the bird gland, is subject to a cholinergic regulation potentially acting via changes in intracellular calcium. In addition to this, secretory activity in both the avian and the turtle glands can be stimulated by a previously undisclosed adenylate cyclase-cyclic AMP system. The identity of the primary signal for such a system is not known, nor is the nature of any interrelationship between the two second-messenger systems that have been identified in these glands.