| This thesis reports pre-clinical molecular pharmacology and physiological effects of novel drugs that interact with the histamine H1 G protein-coupled-receptor (GPCR) to stimulate synthesis of catecholamine neurotransmitters that modulate human cardiovascular and respiratory homeostasis, as well as, neuropsychiatric and neurological functions. Preliminary studies showed the novel compound (-)-(1R,3S)-trans-1-phenyl-3-amino-1,2,3,4-tetrahydronapthalene ([-]-trans-PAT) selectively activates histamine H 1 receptors to stimulate tyrosine hydroxylase (TH), rate-limiting in catecholamine neurotransmitter synthesis, in mammalian forebrain. Studies here characterize H1 signaling activity of (-)-trans -PAT and a new PAT-like analog, (+/-)-(5S,7 R/5R,7S)-cis-5-phenyl-7-dimethylamino-benzocycloheptane ([+/-]-cis-PAB).; Results show that while (+/-)-cis-PAB binds to H, receptors with typical competitive kinetics, binding of (-)- trans-PAT is not competitive. Functionally, (+/-)-cis -PAB is a partial agonist at H1 receptors that stimulate phospholipase (PL) C and intracellular formation of inositol triphosphate (IP) and is a competitive antagonist of H1-mediated activation of adenylyl cyclase (AC) and intracellular CAMP formation. Meanwhile, (-)- trans-PAT is a non-competitive antagonist at H1 receptors that activate PLC/IP formation and a full agonist at H1 receptors that activate AC/CAMP formation. The endogenous agonist histamine activates both H1 signaling pathways.; In rodent brain and bovine adrenal cells, H1-mediated stimulation of TH by (-)-trans-PAT, but not by (+/-)- cis-PAB or histamine, is blocked by inhibition of AC. These results indicate the (-)-trans-PAT effect to stimulate TH is mediated solely through H1 activation of AC and generation of cAMP second messenger while the (+/-)-cis-PAB and histamine effect can be mediated by alternative H1 PLC/IP signaling. Subsequent to formation of cAMP or IP, activation of the TH phosphorylating enzyme protein kinase A (PKA) is critical since inhibition of PKA blocks the TH stimulatory effect of all three ligands---this suggests H1 signaling "cross-talk" downstream of second messenger formation since EP is not know to activate PKA.; This research suggests drugs that are functionally selective at GPCRs may demonstrate potent and efficacious pharmacotherapeutic effects with fewer side effects. For example, as most untoward cardiovascular/respiratory H 1-mediated effects proceed via the PLC/IP pathway, PATs that selectively enhance H1-mediated AC/cAMP signaling provide a mechanistic basis for exploiting H1 receptors as pharmacotherapeutic targets to modulate catecholamine synthesis in neuropsychiatric/neurological disorders. |
