Vasoactive intestinal peptide and cholinergic neurotransmission in the ciliary muscle.
(65/69)The effects of vasoactive intestinal peptide (VIP) on mechanical activity and electrical stimulation of the bovine ciliary muscle in vitro were compared. The generated contractions were enhanced by application of eserine and were abolished completely in the presence of atropine. VIP (10(-8)-10(-6) M) enhanced the response to electrical stimulation, while the contractile amplitude of the ciliary muscle to exogenous carbachol was not altered significantly by application of 10(-7)-10(-6) M VIP. The exogenous VIP had no direct effect on the muscle. As these data indicate that VIP exerts its stimulant effect, prejunctionally, ie, on the nerve terminals, this peptide probably contributes to the control of accommodation as a modulator of cholinergic neurotransmission between short ciliary nerves and the ciliary muscle. (+info)
New methods used to investigate the control of mucus secretion and ion transport in airways.
(66/69)Our group developed two in vivo methods to study secretions from submucosal glands in exposed tracheal epithelium. (1) The exposed mucosal surface was coated with powdered tantalum; accumulated secretions produced elevations (hillocks) in the tantalum layer under which the duct openings were located. The rate of formation of the hillocks was observed through a dissecting microscope, and recorded by television on a video tape recorder. (2) Micropipets were used to collect timed samples from individual gland duct openings. With these techniques, the innervation of the submucosal glands and the autonomic regulation of their secretions were studied. We studied the control of ion movement across tracheal epithelium because active ion transport forms local osmotic gradients across epithelia which could regulate transepithelial water movement. We mounted pieces of the posterior wall of dog trachea in Ussing-type chambers and measured unidirectional fluxes of Cl- and Na+ under short-circuit conditions with 36Cl and 24Na. We found active transport of Cl- toward the lumen and Na+ toward the submucosa. With this technique we investigated the effect of parasympathomimetic drugs on ion movement. With a new in vitro method we studied output of 35S bound to sulfated mucins and movement of ions in cat trachea. We mounted pieces of anterior tracheal wall in Ussing-type chambers, added sodium 35S-sulfate to the submucosal side and monitored secretion of bound 35S in samples from the luminal side after dialysis. The unidirectional fluxes of Cl- and Na+ were measured with 36Cl and 22Na. With this method we examined the effect of alpha-adrenergic and beta-adrenergic agonists on mucin secretion and ion movement. Also with this preparation we studied the relationship between the permeability of the paracellular pathway to 14C-sucrose and the pattern of tight junction strands. (+info)
Microinjection of dynorphin into the supraoptic and paraventricular nuclei produces antidiuretic effects through vasopressin release.
(67/69)The mechanisms for the antidiuretic effects of dynorphin (DYN), an endogenous kappa-agonist, microinjected into the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei were investigated. DYN decreased the urine outflow rate dose-dependently from 5 to 20 nmol in the SON and PVN, and it increased vasopressin release. Microinjection of des-Tyr-DYN (a non-opioid peptide) into the SON produced antidiuretic effects with similar potency to that of the DYN-induced effects. However, in the PVN, the effects of des-Tyr-DYN were very markedly weaker than those of DYN. The DYN-induced antidiureses in the SON were partially inhibited by phenoxybenzamine, timolol and atropine, but not by naloxone. Those in the PVN were partially inhibited by naloxone, timolol and atropine, but not by phenoxybenzamine. Synthetic specific kappa-agonists, U50, 488H and Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-Pro- Arg-Leu-Arg-Gly 5-aminopentylamide (DAKLI), microinjected into the PVN also produced antidiuretic effects in a dose-dependent manner. The order of antidiuretic potency was DAKLI > DYN > U50,488H, which was the same as that of kappa-receptor binding affinity. The DAKLI-induced antidiureses in the PVN were not inhibited by naloxone. These results suggested that DYN caused antidiureses by vasopressin release, through adrenergic and cholinergic mechanisms in the SON and PVN. Only the DYN-induced effects in the PVN were mediated, at least partially, through opioid receptors, perhaps the kappa-subtype. (+info)
Surgical procedure for the cure of atrioventricular junctional ("AV node") reentrant tachycardia: anatomic and electrophysiologic effects of dissection of the anterior atrionodal connections in a canine model.
(68/69)OBJECTIVES: This study was undertaken to examine the electrophysiologic and anatomic effects of a surgical procedure that cures the anterior (common) type of atrioventricular (AV) junctional reentrant tachycardia. BACKGROUND: The procedure was designed to interrupt the reentrant circuit at the point of earliest atrial activation during AV junctional reentrant tachycardia, the anterior atrionodal connections. METHODS: Atrioventricular node function and the sequence of electrical excitation of Koch's triangle were examined in 18 dogs. Excitation of Koch's triangle was mapped using a 60-channel mapping system. Surgical dissection was performed in 10 dogs and a sham procedure in 8. After 28 to 35 days, AV node function and the atrial excitation pattern were reassessed. The AV junction was examined using light microscopy. RESULTS: Some degree of AV node damage was visible in all dogs in the dissection group, but it was minor in 40% of cases. The anterior part of the AV node was disconnected from the anterior atrionodal connections in all cases. Anterograde AV node function was mildly impaired. The median AH interval was increased (62 vs. 76 ms [interquartile ranges 48 to 72 and 64 to 104, respectively], p = 0.05), and the AV Wenckebach cycle length was increased (210 vs. 245 ms [interquartile ranges 200 to 230 and 210 to 260, respectively], p = 0.02). The degree of impairment of conduction was directly proportional to the length of dissection (p < 0.05) but not to the degree of damage to the AV node. Ventriculoatrial (VA) conduction was destroyed in 50% of dogs undergoing dissection but in none of those with a sham operation (p < 0.04). The AV node remained responsive to autonomic blocking drugs, and atrial mapping during ventricular pacing revealed that the site of exit from the AV node had been altered. CONCLUSIONS: The atrionodal connections closest to the His bundle are the preferred route of conduction through the AV node during normal AV or VA conduction. Destruction of these connections modifies AV node conduction. The surgical procedure selectively interrupts these connections, and this interruption is likely to be the mechanism of cure. (+info)
Nitric oxide in the control of submandibular gland function in the anaesthetized ferret.
(69/69)Stimulation of parasympathetic innervation of the submandibular gland (2 or 20 Hz continuously or 20 Hz for 1 s at 10 s intervals), in the ferret, produced secretion of fluid and protein and a fall in vascular resistance. The responses following the administration of N omega-nitro-L-arginine methyl ester (L-NAME; 2 mmol kg-1 i.a.) to block the synthesis of nitric oxide (NO) were reduced, and the persisting responses were abolished (at 2 Hz continuously and 20 Hz intermittently) or further reduced (at 20 Hz continuously) by the additional administration of atropine. The output of vasoactive intestinal peptide (VIP) from the gland was not affected. Neither the secretory nor the vascular response to intra-arterial infusions of acetylcholine (1.25 nmol kg-1) was affected by L-NAME, whereas the vascular responses to both VIP (10 pmol kg-1) and pituitary adenylate cyclase-activating peptide (1-38) (PACAP) (0.5 pmol kg-1) were reduced thereby. Neither peptide evoked a fluid secretion per se. However, when infused during parasympathetic stimulation of saliva secretion, VIP increased both flow rate and the output of protein. These effects of VIP were abolished by L-NAME. The experiments were performed in the presence of sodium nitroprusside at doses (4-8 nmol min-1 kg-1 i.v.) aimed to counterbalance the systemic effects of L-NAME. The results show that, in the ferret, parasympathetic nerve activity increases submandibular blood flow, and elicits the flow of saliva and output of protein by mechanisms that involve in situ generation of NO, upon which the effects of VIP and PACAP but not acetylcholine are largely dependent. (+info)