As this molecule diffuses between cells, it triggers the synthesis of cyclic GMP. Also used by leukocytes to kill bacteria and tumor cells, an overabundance results in shock. It showed that gases could be intercellular messengers when it was found to cause blood vessel dilation, a discovery that led to the 1998 Nobel Prize in physiology.  For ten points, name this driving force behind Viagra, with chemical formula NO.
As this molecule diffuses between cells, it triggers the synthesis of cyclic GMP. Also used by leukocytes to kill bacteria and tumor cells, an overabundance results in shock. It showed that gases could be intercellular messengers when it was found to cause blood vessel dilation, a discovery that led to the 1998 Nobel Prize in physiology.  For ten points, name this driving force behind Viagra, with chemical formula NO.
As this molecule diffuses between cells, it triggers the synthesis of cyclic GMP.
nitric oxide  (do not accept nitrous oxide, which is N2O)