Distribution and function of muscarinic receptor subtypes in the ovine submandibular gland

Abstract

The effects of muscarinic receptor antagonists on responses to electrical stimulation of the chorda-lingual nerve were determined in pentobarbitone-anesthetized sheep and correlated to the morphology of tissue specimens. Stimulation at 2 Hz continuously, or in bursts of 1 s at 20 Hz every 10 s, for 10 min induced similar submandibular fluid responses (19 +/- 3 vs. 21 +/- 3 microl x min(-1) x g gland(-1)), whereas vasodilatation was greater during stimulation in bursts (-52 +/- 4 vs. -43 +/- 5%; P < 0.01). Continuous stimulation at 8 Hz induced substantially greater responses (66 +/- 9 microl x min(-1) x g gland(-1) and -77 +/- 3%). While atropine (0.5 mg/kg iv) abolished the secretory response at 2 and 20 Hz (1:10 s), a small response persisted at 8 Hz (<5%). The "M1-selective" antagonist pirenzepine (40 microg/kg iv) reduced the fluid response at all frequencies tested (P < 0.05-0.01), most conspicuously at 2 Hz (reduced by 69%). Methoctramine ("M2/M4-selective"; 100 microg/kg iv; n = 5) had no effect on fluid or the vascular responses but increased the protein output at 2 (+90%, P < 0.05) and 8 Hz (+45%, P < 0.05). The immunoblotting showed distinct bands for muscarinic M1, M3, M4, and M5 receptors, and immunohistochemistry showed muscarinic M1 and M3 receptors to occur in the parenchyma. Thus muscarinic M1 receptors contribute to the secretory response to parasympathetic stimulation but have little effect on the vasodilatation in the ovine submandibular gland. Increased transmitter release caused by blockade of neuronal inhibitory receptors of the M4 subtype would explain the increase in protein output.

Muscarinic Receptor Subtypes in the Lower Urinary Tract

“…In spite of a M 3 -selective profile, many anticholinergics are only capable of discriminating the human muscarinic M 3 subtype from the M 1 and M 5 subtypes with an affinity factor of 1-16 [161][162][163][164] . The common side effect of anticholinergic therapy against overactive bladder is a dry mouth [149,165] , and, since muscarinic M 1 receptors exert secretory effects, muscarinic M 3 receptor-selective antagonists would tentatively result in fewer incidences of this adverse effect [150,166,167] .…”

Activation of transient receptor potential vanilloid subtype 1 increases secretion of the hypofunctional, transplanted submandibular gland

“…Blood flow is one of the most important factors affecting the secretion of the submandibular gland (33,34). We measured the glandular blood flow of transplanted submandibular glands before and after capsaicin treatment.…”

Characterization of Prejunctional Muscarinic Receptors: Effects on the Release of VIP and Functional Responses and Receptor Expression in the Ovine Submandibular Gland

“…Anaesthesia was induced and maintained with sodium pentobarbitone (Sagatal, Rhône Mérieux Ltd., Harlow, UK; 15–30 mg kg −1 IV (via a catheter in the femoral vein) and then 0.1–0.3 mg min −1  kg −1 IV (adjusted to maintain a stable blood pressure)). Surgery was performed as been described previously [1]. In short, the trachea was intubated, and the ipsilateral ascending cervical sympathetic nerve was cut.…”

“…The fluid secretory response of the ovine submandibular gland to acetylcholine is exerted via both muscarinic M1 and M3 receptors, while M5 receptors also seem to participate in the cholinergic vasodilator response [1]. However, in the parasympathetic glandular neurons, the neuropeptide vasoactive intestinal peptide (VIP) may be colocalised with acetylcholine [2].…”

“…The crosstalk between the two transmitter substances occurs at prejunctional level also [6, 16, 17]. In the ovine submandibular gland, intravenous injections of the “M2/4”-selective antagonist methoctramine significantly increased the parasympathetic nerve-evoked secretion of protein [1]. Also, unselective muscarinic receptor blockade of prejunctional receptors has been shown in a number of species to increase VIPergic responses together with the release of VIP upon electrical stimulation of the parasympathetic glandular innervation [6, 18, 19].…”