Presynaptic alpha-receptor control of adrenergic transmitter release in blood vessels

The presynaptic alpha-adrenergic receptor control of transmitter release in vascular tissues is discussed. A model of adrenergic innervation of the vascular bed is proposed based on ultrastructural and histochemical evidence. Evidence is presented to support the concept of intermittent or periodic release of norepinephrine (NE) from the varicosity. Intermittency combined with a mechanism such as presynaptic control to ensure spatial distribution of release sites, along with a slow effector response and recovery, results in a smooth, generalized change in tone and an overall economy of transmitter. The effective concentration of NE around the presynaptic membrane is maintained for considerably less than 0.1 s. It is argued that the transient presence of transmitter in the synapse combined with intermittency of release does not favor accumulation of transmitter at the cleft at physiological frequencies or desensitization of presynaptic receptors. In addition, intermittency provides an explanation for why exogenous NE is more effective presynaptically in influencing release than endogenous NE. The importance of cleft width in presynaptic control of transmitter release, the possible complications caused by facilitation, and resolution of some apparent problems with the presynaptic hypothesis are also discussed.     

Alpha 1 adrenergic receptor control of renal blood vessels during aging

Aging humans and rats have a reduced renal vascular constriction response to stress, change in posture, or exercise. In this study, renal interlobar arteries from 9- (intermediate age) to 15-month-old (aging) male Wistar rats constricted less to alpha-adrenergic agonists than those of 4-month-old (young adult) rats. The reduced contraction to A61603 (alpha 1 A agonist) was similar to that to norepinephrine and phenylephrine. Therefore, it appears that the reduction in constriction is primarily related to alpha 1 A receptor stimulation. GeneChip microarray hybridization analysis of the interlobar arteries with the RAE 230A GeneChip indicated that there were no significant differences in gene expression for alpha 1 A/C, 1B, or 1D receptors between 4-month-old (young adult) and 1-year-old (aging) male Wistar rats. Competitive binding experiments (prazosin) revealed that maximal binding (Bmax, fmol/mg protein) of the alpha 1 receptors of interlobar arteries was reduced 25% by 10 months of age and 50% by 18+ months of age. Alpha 1 receptor-induced arterial constriction and prazosin binding were both down-regulated. The loss of receptor-initiated constriction likely includes down-regulation of maximum agonist binding by alpha 1 adrenergic receptors.     

Quantitative analysis of the density and pattern of adrenergic innervation of blood vessels

Summary Automated quantitative image analysis (QIAF) was used to measure and compare the adrenergic nerve plexuses of 4 blood vessels from the guinea pig, demonstrated by glyoxylic acid fluorescence (GAF). The results showed considerable quantitative variation of plexus density, size of bundles, and numbers of varicosities. A range of alternative procedural and anatomical sources of variability were investigated and assessed. The carotid artery was found to have a dense plexus with more nerves than that of the mesenteric artery; the mesenteric vein and abdominal aorta had sparse plexuses. The carotid artery plexus, despite the density of its nerves, possessed only half the number of varicosities of the mesenteric artery plexus. This sparse varicosity population was shown to have a similar density to the varicosities demonstrated by QIAF in the scattered nerves of the mesenteric vein and abdominal aorta. QIAF confirmed visual estimates of adrenergic plexus density, and was able to demonstrate less obvious differences of nerve density and size, and varicosity populations, between the different plexuses studied. The method is applicable to stretch preparations and transverse sections of many adrenergically innervated tissues.     

A note on the mathematical theory of vibrations of walls of blood vessels

Periodic vibrations of the walls of a distensible elastic tube through which a fluid is flowing are studied by the method used by Lord Rayleigh in his theory of vibrations of jets. The results are found to conform with those obtaine previously by a more general but approximate method.     

Three dimensional observation of the nerve fibers along the cerebral blood vessels

Three dimensional observation of the nerve fibers along the cerebral blood vessels was investigated by scanning electron microscopy. Electron probe X-ray microanalysis was also performed in the cerebral blood vessels treated with peroxidase-antiperoxidase immunohistochemistry intensified by nickel ammonium sulfate. Nerve fibers (2-8 microns in diameter) formed a plexus on the outer surface of the adventitia. After branching, the nerve fibers penetrated the blood vessel adventitia. Substance P-immunoreactive nerve fibers showed a meshwork pattern in the outer layer of the adventitia, and vasoactive intestinal polypeptide (VIP)-immunoreactive nerve fibers revealed a spiral running pattern in the inner layer of the adventitia. Taken together with previous studies, these findings suggest that substance P nerve fibers in the cerebral arteries may not be related to arterial dilatation or constriction, but VIP nerve fibers may be vasodilative.     

Three dimensional observation of the nerve fibers along the cerebral blood vessels

Summary Three dimensional observation of the nerve fibers along the cerebral blood vessels was investigated by scanning electron microscopy. Electron probe X-ray microanalysis was also performed in the cerebral blood vessels treated with peroxidase-antiperoxidase immunohistochemistry intensified by nickel ammonium sulfate.Nerve fibers (2–8 m in diameter) formed a plexus on the outer surface of the adventitia. After branching, the nerve fibers penetrated the blood vessel adventitia. Substance P-immunoreactive nerve fibers showed a meshwork pattern in the outer layer of the adventitia, and vasoactive intestinal polypeptide (VIP)-immunoreactive nerve fibers revealed a spiral running pattern in the inner layer of the adventitia. Taken together with previous studies, these findings suggest that substance P nerve fibers in the cerebral arteries may not be related to arterial dilatation or constriction, but VIP nerve fibers may be vasodilative.     

Spiral arrangement of muscular elements in the walls of blood vessels and their role in hemodynamics

The article claims that contractions of the cardiac left ventricle produce a whirling (turbulent) movement of blood that is maintained in the aorta. In the walls of large and small arteries, as well as in the arteriolar walls, myocytes have a spiral arrangement. Their contraction maintains the turbulent blood stream in the vessels with a small diameter, in spite of the fact that the Reinolds' number for them is rather small. The author considers that while making a mathematical analysis of the blood flowing in the arteries, it is necessary to take into account that the walls of the arterial vessels actively influence the blood stream.     

Prostacyclin producing activity of human umbilical blood vessels in adrenergic innervated and non-innervated portions

The present experiment was performed in order to clarify the significance of prostacyclin (PGI2) in the regulation of human umbilical blood flow. Distribution of adrenergic nerve fibers in umbilical cord was examined by means of a modification of the glyoxylic acid fluorescence histochemical technique. PGI2 producing activity in various portions of umbilical blood vessels was measured by platelet bioassay. Adrenergic nerve fibers were observed only in the region surrounding umbilical arteries at the fetal end of the cord. PGI2 producing activity of umbilical arteries was significantly lower in the innervated region than in the non-innervated region. There were no significant regional differences in umbilical vein which has no adrenergic innervation. The relationship between vascular PGI2 producing activity and adrenergic innervation, and the significance of PGI2 in the regulation of human umbilical blood flow are discussed.     

Ultrastructural immunolocalization of elastic fibers in rat blood vessels using the protein A-gold technique

Identification of elastic fibers at the ultrastructural level is accomplished by a post-embedding immunohistochemical technique using the protein A-colloidal gold method. Antisera against elastins from human dermis and rat aorta have been characterized by radioimmunoassay and then applied to thin sections of rat blood vessels. Two fixative solutions and two embedding media have been tested. Both antibodies bind to elastic fibers of normal arteries and veins, indicating crossreactions among organs and species. The high sensitivity of this method is demonstrated by its application to the detection of neo-elastogenesis in the intimal thickening of aortic grafts.     

Distribution of catecholamine-containing nerve cells in the walls of the major vessels of the lamprey, Lampetra fluviatilis

Using histochemical fluorescence technique, two types of adrenergic nervous cells, i.e. small with intense fluorescence and large with weak fluorescence, have been detected in tissues and walls of the main blood vessels in the lamprey Lampetra fluviatilis. The first type of cells is distributed along the whole vascular net concentrating mainly in branching nodes. The second type of cells was found only in the adventitial layer of the dorsal aorta and intestinal artery. Adrenergic nervous cells are also present in the walls of the main veins. Possibility of presence of catecholamines of different nature in the bodies of the nerve cells is discussed.     

Method of combined detection of nerve fibers and blood vessels in nerve trunks]

A new method for investigation of neuro-vasal relationships in nerve conductors is proposed based on a combination of the fine injecting of their blood vessels and staining the nerve fibres. The vessels are injected with the chloroform emulsion of finely ground Paris blue (5-10 g per 100 g of solvent). Pieces of nerves 0,5 cm thick are fixed in 12% neutral formalin for 3 days, kept in a dark vessel in Weigert's mortant for 5 days, dehydrated and imbedded in paraffin. Thin slices 4-5 micronkm thick are stained in hematoxylin after N. N. Kulchitski, differentiated for 2-12 h in the mixture containing 1% solution of potassium ferricyanide and saturated solution of lithium carbonate (1:10) and after passing through alcohols of increasing concentration and xylene imbedded in balsam. In the preparations the fibres of different caliber are stained grey and the vessels are stained blue.