Depletion of secretory granules from the feline parotid gland: action of NANC transmitters per se

Abstract

A parotid acinar degranulation of approximately 60 and 40% was observed in cats under pentobarbitone anaesthesia after a 90-min period of continuous stimulation of the parasympathetic auriculo-temporal nerve at 10 Hz in the absence and presence of atropine, respectively. Atropine completely abolished the large fluid response of the gland to the nerve stimulation. In the non-atropinized cats, bethanechol, infused into the carotid artery at a dose rate evoking a salivary flow similar to that in response to parasympathetic nerve stimulation, caused an acinar degranulation of approximately 25% and acinar vacuolation. Vasoactive intestinal peptide (VIP; 0.5 microgram kg-1 min-1 also infused into the carotid artery for 90 min) caused an acinar degranulation of the same magnitude as the parasympathomimetic drug but the peptide did not give rise to any fluid secretion or vacuole formation. The experiments were performed in the presence of alpha- and beta-adrenoceptor blockers. Thus, in parotid glands of the cat, producing no overt secretion of fluid, non-adrenergic, non-cholinergic (NANC) mechanisms may be at work causing exocytosis of the acinar granules. These mechanisms are also likely to contribute to the secretion of granules in response to parasympathetic nerve activity in the absence of blockade of the classical autonomic receptors.

Effect of the neuropeptides vasoactive intestinal peptide, peptide histidine methionine and substance P on human major salivary gland secretion

“…The appearance of the peptide‐stimulated mucous cells was similar to that in response to carbachol, also previously described in the human submandibular gland (Riva et al , ). Thus, humans belong to those species (rat, cat, dog, ferret, pig, sheep, mink and calf) in which VIP causes the acinar cells of salivary glands to lose secretory granules and to release proteins/glycoproteins, and when administered in vivo , during ongoing secretion, causes the flow rate to accelerate and the salivary protein concentration to increase (Lundberg et al , ; Inoue and Kanno, ; Reid and Heywood, ; Reid and Titchen, ; Bobyock and Chernick, ; Ekström and Tobin, , ; Tobin et al , ; Turner and Camden, ; Ekström et al , ; Culp and Richardson, ; Calvert et al , ; Ekström and Ekström, , ). So far, the rat and the mink are the only species where VIP per se , in addition, has been found to evoke an overt flow of saliva (Ekström et al , ; Tobin and Ekström, ).…”

“…In contrast to VIP, the secretory effect of SP (and its related non‐mammalian tachykinin physalaemin) appears to be limited to a few species, where the output of proteins is accompanied by a lively flow of saliva. The release of proteins in response to VIP and SP is morphologically reflected by the loss of storage granules from the acinar cells (Ekström et al , ; Ekström and Ekström, , ; Del Fiacco et al , ).…”

Purinergic P2X7 Receptors Mediate ATP-induced Saliva Secretion by the Mouse Submandibular Gland

“…The authors concluded that the flow rate was produced by vasoactive intestinal peptide (VIP) release (25), however this seems unlikely since VIP receptor activation is linked to an increase in cAMP, not [Ca 2ϩ ] i . Indeed, Ekstrom et al (26) reported that VIP treatment caused little to no fluid secretion in feline parotid glands. Interestingly, the electrically evoked "atropine-resistant" fluid secretion was ϳ30% of the response prior to muscarinic receptor inhibition in the ferret submandibular gland (3).…”

Non‐adrenergic, non‐cholinergic influences on parotid acinar degranulation in response to stimulation of the parasympathetic innervation in the anaesthetized rat

“…However, the significant (P < 0.05) difference between non-atropinized and atropinized rats subjected to the long-term period of stimulation may nevertheless indicate some loss of granules in the non-atropinized animals during the last 40 min. The observation that the rate of depletion of the parotid gland content of some neuropeptides, including substance P and VIP, in response to stimulation of the parasympathetic innervation is lower in the absence of atropine than in its presence (Tobin et al 1994) may be important in this connection. Positive interactions between agonists may also be important.…”

“…In the rat, exogenous VIP evokes a small flow of parotid saliva (Ekstrom, Mansson & Tobin, 1983), very rich in protein and, in the feline parotid gland, VIP has been shown to release acinar secretory granules (Ekstrom, Asztely, Helander & Tobin, 1994). Concomitantly with the decrease in the glandular content of VIP, there is also a marked decrease in the content of parasympathetic postganglionic substance P. In the rat, substance P evokes a large flow of parotid saliva with a low concentration of protein (Ekstrom & Wahlestedt, 1982;Ekstrom et al 1983;Ekstrom & Olgart, 1986).…”