Islet constitutive no synthase. biochemical determination and
regulatory function.
Salehi, Albert, Mats Carlberg, Ragnar Henningson, and Ingmar
Lundquist.
Department of Pharmacology and Department of Zoology, University of
Lund, Lund, Sweden
APStracts 2:0446C, 1995.
Recent immunohistochemical findings, suggested that a constitutive NO
synthase (cNOS) resides in endocrine pancreas. Here we provide direct
biochemical evidence for the presence of cNOS activity in isolated
islets. The regulating influence of this NOS activity for islet
hormone release was also investigated. We observed that cNOS activity
could be quantitated in islet homogenates by monitoring the formation
of L-citrulline from L-arginine using an Amprep CBA cation-exhange
minicolumn prior to derivatization with o-phtaldialdehyde and
subsequent HPLC analysis. The islet NOS was dependent on both Ca2+
and calmodulin and suppressed by the NOS inhibitor NG-nitro-L
-arginine methylester (L-NAME). This effect was enantiomerically
specific. Islet insulin release induced by a mixture of L-arginine
and glucose was enhanced by L-NAME, whereas L-arginine-induced
glucagon release was inhibited. The effect of L-NAME on insulin
release was dose-dependently potentiated by increasing glucose
concentrations, suggesting that glucose is an important regulator of
islet NO production. Complementary in vivo studies showed similar
results; i.e. the insulin secretory response to a mixture of glucose
and L-arginine was extremely enhanced by pretreatment with L-NAME
whereas L-arginine-stimulated glucagon response was suppressed.
Finally, in isolated islets, the intracellular NO donor hydroxylamine
suppressed insulin release and increased glucagon release. In
summary, the islets of Langerhans contain a constitutive,
Ca2+/calmodulin dependent isoform of NOS. Islet NO suppressed insulin
but enhanced glucagon secretion. The data also suggest a negative
feedback by NO on glucose-induced insulin release. The islet NO
system is a novel and important regulatory factor in insulin and
glucagon secretion.
Received 22 June 1995; accepted in final form 6 December 1995.
APS Manuscript Number C365-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 December 95