Abstract
Mammalian pineal gland receives peptidergic (e.g., vasoactive intestinal peptide [VIP]; peptide histidine isoleucine [PHI]; neuropeptide Y, NPY; substance P, calcitonin gene-related peptide [CGRP], arginine vasopressin [AVP] and oxytocin [OXT]) fibers in addition to sympathetic innervation. The dynamics of cAMP efflux and melatonin (MT) secretion were compared during the infusion of these peptides in our long-term perifusion system. VIP and PHI enhanced both pineal cAMP efflux and MT secretion in a dose-dependent manner (10 nM to 10 microM). However, the potency of PHI was slightly less. The peak of cAMP release always precedes that of MT production. The possible interactions between adrenergic and peptidergic compounds in the regulation of pineal cAMP efflux and MT secretion were also studied. VIP acts on specific peptidergic receptors, since its stimulatory effect could only be reduced by a VIP receptor antagonist. VIP has an additive effect at a lower (100 nM) concentration combined with norepinephrine (NE). NPY (100 nM) can completely block NE-induced MT secretion, but the decrease in cAMP efflux is less. However, NPY does not significantly influence VIP-stimulated cAMP efflux or MT secretion. These data suggest that NE, VIP, and NPY are differently involved in the cAMP and calcium signaling. The other neuropeptides are ineffective.
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