Neuropeptide Y in salivary glands of the rat: origin, release and secretory effects

Abstract

In the parotid gland, double immunostaining showed the perivascular and most of the periductal neuropeptide Y (NPY)-immunoreactive nerve fibres to contain dopamine β-hydroxylase, while the majority of periacinar NPY-fibres contained vasoactive intestinal peptide. Sympathectomy caused a marked depletion of perivascular and periductal NPY-fibres, leaving periacinar NPY-fibres less affected. Following combined sympathectomy and parasympathectomy, only a few NPY-fibres persisted. The parasympathetic auriculo-temporal nerve contributed most (75%) and the cervical sympathetic nerve least (15%) to the parotid gland content of NPY as judged by radioimmunoassay. The sensory neurotoxin capsaicin was without effect on the occurrence and gland content of NPY. Upon long-lasting electrical stimulation of the auriculo-temporal nerve at a high frequency, the gland content of NPY was reduced (by 55%), a depletion thought to indicate release of the peptide from parasympathetic nerve terminals. In vitro, tissues of parotid, submandibular and sublingual glands released concentration-dependently protein (and as to the parotid gland amylase also) in response to NPY; the protein response was largest from sublingual tissue (per unit weight). A concentration-dependent in vitro release of potassium from tissues of parotid and submandibular glands in response to NPY occurred and here, submandibular gland tissue was the most sensitive. Comparisons between the action of some secretagogues (at 10 −6 M) showed NPY to be less effective than vasoactive intestinal peptide and adrenaline, but as effective as bethanechol and substance P, in releasing protein (and amylase) in parotid and submandibular gland tissues; in sublingual gland tissue NPY was less effective than vasoactive intestinal peptide, in the range of adrenaline and more effective than bethanechol and substance P. As to potassium release (at agonist concentration of 10 −6 M) from tissues of parotid and submandibular glands NPY was less effective than substance P and vasoactive intestinal peptide. The fluid response to NPY upon i.v. administration was scanty from parotid and submandibular glands. NPY is likely to play a complementary role in mediating parasympathetic secretory responses in salivary glands of the rat. It seems preferentially involved in the control of protein secretion.