Extrinsic innervation of the canine superior vena cava, pulmonary, portal and renal veins

Some embryological aspects of cholinergic innervation in the cardiovascular system--a close association with the subintestinal circulatory channel

A series of our studies on the dog venous system revealed that cholinergic excitatory innervation was localized in a group of veins: the portal, mesenteric, and hepatic veins and the middle segment of the inferior vena cava. Our studies on pharmacological responsiveness of dog veins also revealed that they could be divided into two groups: the visceral and somatic parts, and the cholinergic excitatory innervation localized to the visceral part. Considering these results and some relevant literature, a hypothesis is proposed on the classification of muscles of the cardiovascular system and some embryological aspects of the parasympathetic cholinergic innervation in the circulatory system are discussed. The embryonic circulatory system of vertebrates can be divided into two parts: somatic and visceral. The body of an embryo is regarded as a double tube and vessels of the visceral part and the heart belong to the inner tube. The muscle of these vessels and the heart are derived from visceral mesoderm, either the coelomic epithelium or mesenchymal cells, in common with muscle of the digestive tube; and thus the parasympathetic cholinergic nerves innervating the muscle of the digestive tube also distribute to these vessels and the heart. The heart and vascular muscles in the visceral part are structures developed early in the course of evolution in invertebrates. Their primary function is to propel the body fluid, and the chief structure containing them is the subintestinal circulatory channel (ventral aorta - heart - subintestinal vein). They exhibit spontaneous, rhythmic activity, showing characteristics of a single unit muscle, and receive parasympathetic cholinergic innervation. On the other hand, the vascular muscles in the somatic part are endothelium-associated muscles developed anew in the vertebrate; do not contract spontaneously, being classified as a multiunit muscle; and lack parasympathetic cholinergic innervation.

Mediation by the same muscarinic receptor subtype of phasic and tonic contractile activities in the rat isolated portal vein

1. The effects of several agonists on the phasic and tonic contractile responses to muscarinic receptor stimulation have been investigated in the rat portal vein in vitro. 2. Neither chemical denervation with 6-hydroxydopamine nor the presence of the alpha 1-adrenoceptor antagonist, prazosin, influenced the spontaneous or the stimulated myogenic activity of the portal vein. 3. Indomethacin and NG-nitro-L-arginine were used to investigate the influence of vasoactive factors in this preparation. They slightly increased the frequency and the amplitude of the spontaneous myogenic activity of the portal vein, respectively. NG-nitro-L-arginine but not indomethacin enhanced the maximal phasic response to carbachol. Both indomethacin and NG-nitro-L-arginine failed to influence the tonic response to carbachol. 4. Muscarinic agonists increased phasic activity according to the rank order of potency: acetylcholine > muscarine > methacholine > carbachol > aceclidine > bethanechol. These effects were superimposed on a sustained contracture at higher concentrations. Oxotremorine was more potent than arecoline in increasing the mechanical phasic activity, without inducing a sustained contracture. Pilocarpine and McN A343 were weak agonists, producing submaximal effects only on phasic activity. 5. The muscarinic antagonists AF-DX116, 4-diphenylacetoxy-N-methylpiperidine (4-DAMP), P-fluorohexahydrosiladiphenidol (pFHHSiD) and pirenzepine antagonized the phasic and tonic mechanical responses to carbachol. Although the tonic contracture was slightly more sensitive to all antagonists studied, the rank order of potency: 4-DAMP > pFHHSiD > pirenzepine > AF-DX 116 was the same for both types of responses, which is indicative of a M3-receptor subtype. 6. The tonic contractile response of the rat portal vein to carbachol was more susceptible to partial receptor inactivation with propylbenzilylcholine mustard than the phasic contractile response. The dissociation constants (KA) obtained from an analysis according to Furchgott & Bursztyn (1967) were found to be 4.32 +/- 0.31 1AM for the phasic and 3.56 +/- 0.21 1AM for the tonic type of carbachol-induced response, respectively. Since the EC50-values for both carbachol-induced effects were different (phasic0.232 +/- 0.02 1AM; tonic 2.75 +/- 0.1 1AM) the phasic type of response appears to involve a large receptor reserve.

Central vasomotor control of the rabbit portal vein

Contractile responses of the portal vein of the anesthetized rabbit were measured quantitatively by plethysmography during transmural electrical field stimulation (TES, 0.8 ms and 15 V) and during the cerebral ischemic pressor response at various volemic states. To evoke the cerebral ischemic response, the route of blood supply to the brain was surgically restricted to the right internal carotid artery, the artery was then compressed in a stepwise fashion by a micrometer device. The maximum contractile response of the portal vein segment that could be evoked by cerebral ischemia corresponded in magnitude to that produced by TES of 10-11 Hz. The contractile response began when the internal carotid blood flow was reduced to 4 ml/min from its normal value of 13.8 +/- 1.2 (mean +/- SE) ml/min and reached a maximum at 0 ml/min. The maximum contractile response was an increase of 26% from control value under normovolemic condition, 20% after hemorrhage and 31% after volume loading. It was estimated that the contractile response in normovolemia was 95% neurogenic, the rest was thought to be of humoral origin.