AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 2 439-R446, Copyright © 1993 by American Physiological Society
Neuropeptide Y inhibits chloride secretion in the shark rectal gland
P. Silva, F. H. Epstein, K. J. Karnaky Jr, S. Reichlin and J. N. Forrest Jr
Department of Medicine, New England Deaconess Hospital, Boston 02215.
We studied the effects of the 36-amino acid peptide, neuropeptide Y (NPY),
on salt secretion by the rectal gland of Squalus acanthias. We used three
preparations: whole isolated perfused glands, freshly prepared separated
rectal gland tubules, and confluent monolayers of cultured rectal gland
cells. In perfused glands NPY inhibited secretion stimulated by vasoactive
intestinal peptide (VIP), forskolin, or adenosine 3',5'-cyclic
monophosphate (cAMP) and theophylline. Maximal inhibition of 63 +/- 3.4%
was seen at 3 x 10(-8) M NPY, with half-maximal effect at 3 x 10(-9) M. NPY
did not inhibit the basal activity of rectal gland adenylate cyclase or
that stimulated by VIP. The inhibitory action of NPY was not prevented by
procaine, nifedipine, or diltiazem, suggesting that it was not secondary to
the release of somatostatin or other unknown neurotransmitters from rectal
gland nerves. In confirmation, somatostatin was not detected in the venous
effluent after administration of NPY. NPY also inhibited transport-related
oxygen consumption in separated rectal gland tubules and inhibited
short-circuit current generated by confluent monolayers of primary cultures
of rectal gland cells. The results indicate that NPY inhibits chloride
secretion by a direct action on cells of the shark rectal gland at a site
distal to the generation of cAMP.
