AJP - Regulatory, Integrative and Comparative Physiology, Vol 249, Issue 3 348-R354, Copyright © 1985 by American Physiological Society
Atriopeptin stimulation of rectal gland function in Squalus acanthias
R. Solomon, M. Taylor, D. Dorsey, P. Silva and F. H. Epstein
The rectal gland of the shark plays a significant role in the homeostasis
of extracellular volume. Regulation of rectal gland function is under
hormonal control, but the precise identity of the humoral mediator is
unknown. Atriopeptin stimulates rectal gland chloride secretion in vivo.
This stimulation of epithelial transport is accompanied by systemic and
local hemodynamic effects. Atriopeptin also stimulates chloride secretion
by the in vitro perfused rectal gland, an effect that is not accompanied by
hemodynamic changes. Extracts of shark heart, but not muscle, brain,
kidney, or intestine, contain a heat-stable trypsin-sensitive substance
capable of in vitro stimulation of rectal gland chloride secretion.
Electron micrographic analysis reveals multiple neurosecretory-like
granules in atrial cardiocytes that are only rarely seen in ventricular
cardiocytes. By using the in vitro perfused gland as a biologic assay,
serum obtained after extracellular volume expansion reveals the presence of
a rectal gland stimulatory factor that is not present in serum before
expansion. These results are consistent with the hypothesis that
atriopeptin is present in shark cardiocytes and is released during volume
expansion. The atriopeptin stimulates rectal gland chloride secretion,
providing a negative feedback mechanism for the regulation of extracellular
volume.
