The Labial Gland: A Salt-Secreting Organ of Saturniid Moths

Abstract

1. The labial gland of adult saturniids produces a voluminous liquid at about the time of ecdysis, in response to either confinement of the moth or physostigmine injection. This liquid normally facilitates escape from the cocoon. 2. During secretion the gland accumulates K⁺ and HCO₃^- from the blood, and Rb⁺ if it is available, but excludes rather efficiently Na⁺, Li⁺, Sr²⁺, Ca²⁺, Mg²⁺, phosphate and other small molecular weight components of blood. Cl^- is approximately equally distributed in blood and secretion. 3. The pH of the secretion is approximately 8.5, as compared with 6.5 for blood. 4. The secretion is in osmotic equilibrium with blood, even after alteration of blood osmotic pressure by injection of hypertonic or hypotonic solutions. 5. For both Cl^- and Na⁺ the rate of entry into the secretion is proportional to concentration in blood; i.e. the efficiency of exclusion is characteristic for each ion, within a wide range of blood concentrations. 6. Secretion is accompanied by a potential difference across the secretory cell (ca.+25 mV. lumen positive). Secretion is abolished by dinitrophenol, but not by ouabain or acetazoleimide. 7. The results are best explained in terms of a respiration-mediated active accumulation of blood K⁺, in exchange for H⁺, in the basal region of the cells; this is presumably followed by release of the K⁺ into the lumen, with concomitant reabsorption of H⁺ from the secretion. The alkaline secretion then traps blood CO₂ by converting it to HCO₃^-. Water follows osmotically, and other ions enter passively, at a rate determined by the corresponding permeability of the cells.