AJP - Regulatory, Integrative and Comparative Physiology, Vol 246, Issue 1 63-R66, Copyright © 1984 by American Physiological Society
In vivo effect of volume expansion on rectal gland function. I. Humoral factors
R. Solomon, M. Taylor, J. S. Stoff, P. Silva and F. H. Epstein
The spiny dogfish Squalus acanthias responds to volume expansion by
increasing the rate of chloride secretion by its rectal gland. The response
is elicited by intravascular infusion of either isotonic shark Ringer
solution, a 1 M hypertonic sodium chloride solution, or an isotonic
hyponatremic solution containing equal volumes of shark Ringer solution and
10% mannitol. The effect of volume expansion was evoked in explanted glands
connected to a host fish only by the arterial supply, indicating that the
response is mediated by a humoral factor. The explanted gland responded to
theophylline (2.5 X 10(-3) M) and adenosine 3',5'-cyclic monophosphate (5 X
10(-4) M) by increasing the rate of secretion of chloride by an amount
similar to that induced by volume expansion of the perfusing fish.
Theophylline at concentrations (10(-6) to 5 X 10(-5) M) that are known to
inhibit the effect of adenosine in isolated perfused glands failed to
inhibit the effect of volume expansion on explanted glands. Somatostatin
(4.5 X 10(-6) M), which inhibits the effect of vasoactive intestinal
peptide (VIP) in the isolated perfused gland, completely prevented the
secretory response to volume expansion in explanted glands. Volume
expansion is a major stimulus for chloride secretion by the rectal gland.
The effect is mediated by a humoral factor that appears to be VIP.
