Nature and location of the receptors for salt‐gland secretion in the goose

Abstract

1. The nature and location of the receptors which stimulate salt-gland secretion in the goose have been investigated.2. The rapid injection of homologous blood (sufficient to raise the blood volume by 16 and 9%) into the right atrium failed to induce secretion. In contrast, hypertonic sucrose, Na(2)SO(4) and LiCl initiated secretion.3. These results support the theory that osmoreceptors initiate secretion by detecting an increase in plasma tonicity.4. The minimal amount of hypertonic NaCl required to initiate secretion when infusions were made into a carotid artery or into various arteries and veins in the splanchnic region was not less than that required by an I.V. route.5. Cross-circulation and perfusion studies also showed that a raised [NaCl] in the blood perfusing the head was ineffective in evoking secretion and thus that plasma tonicity must be raised elsewhere in the body.6. Secretion in response to salt-loading was abolished or prevented by cutting the vagus nerves or blocking them with local anaesthetic. Stimulation of the cephalic end of the cut vagi in an isolated, perfused decerebrate head induced secretion, indicating that the afferent fibres from the receptors to the C.N.S. lie in the vagus nerves. Cutting the vagi below the heart, however, had no effect on the secretory response.7. Blocking nerves in the crop with local anaesthetic had no effect on secretion induced by salt-loading but when local anaesthetic was injected into the pericardial sac, secretion decreased immediately, stopped, and recovered with a time course similar to that seen after blocking the vagus nerves.8. Section of the vagi in the neck abolished the tachycardia observed in response to the injection of hypertonic NaCl into the right atrium.9. As in other species, stimulation of the ;secretory nerve' induced secretion in anaesthetized or decerebrate geese.10. Hexamethonium given I.V. or applied topically to the ;secretory nerve ganglion' blocked secretion in response to salt-loading or to secretory nerve stimulation.11. It appears that the receptors for salt-gland secretion are located in or near the heart and that afferent fibres from these receptors travel in the vagus nerves to the C.N.S.12. A possible scheme of the secretory reflex which initiates and maintains salt-gland activity is proposed.