The Chemical Transmission of Vasoconstrictor Impulses to the Hind Limbs and the Splanchnic Region of the Cat

Sympathetic and Sensory-Motor Nerves in Peripheral Small Arteries

Small arteries, which play important roles in controlling blood flow, blood pressure, and capillary pressure, are under nervous influence. Their innervation is predominantly sympathetic and sensory motor in nature, and while some arteries are densely innervated, others are only sparsely so. Innervation of small arteries is a key mechanism in regulating vascular resistance. In the second half of the previous century, the physiology and pharmacology of this innervation were very actively investigated. In the past 10-20 yr, the activity in this field was more limited. With this review we highlight what has been learned during recent years with respect to development of small arteries and their innervation, some aspects of excitation-release coupling, interaction between sympathetic and sensory-motor nerves, cross talk between endothelium and vascular nerves, and some aspects of their role in vascular inflammation and hypertension. We also highlight what remains to be investigated to further increase our understanding of this fundamental aspect of vascular physiology.

Pharmacological Actions of Hemlock (Conium Maculatum) Alkaloids

The actions of three hemlock alkaloids—coniine, N-methylconiine and α-coniceine—have been examined on isolated tissues, on anaesthetised cats and hens and on conscious mice and young chicks. The most pronounced action of the alkaloids was to block spinal reflexes by an action exerted in the spinal cord. Their peripheral actions on autonomically innervated structures were mainly a consequence of an initial stimulant and a secondary depressant action on autonomic ganglia. Large doses of the alkaloids stimulated skeletal muscle and subsequently caused neuromuscular block. This blocking action differed in many respects from that produced by decamethonium or tubocurarine.

Neuropeptide Y Y1 receptors in vascular pharmacology

The existence of neurogenic mediator candidates apart from noradrenaline and acetylcholine involved in the control of vascular tone has attracted enormous attention during the past few decades. One such mediator is neuropeptide Y (NPY), which is co-localized with noradrenaline in sympathetic perivascular nerves. Stimulation of sympathetic nerves in vitro and in vivo causes non-adrenergic vasoconstriction which can be blocked by experimental manipulations that inhibit NPY mechanisms. Thus, the vasopressor response to stimulation of sympathetic nerves can be attenuated by chemical or surgical sympathectomy, treatment with reserpine or other pharmacological agents, and tachyphylaxis to NPY or by NPY antagonists. The NPY field was long plagued by a lack of specific antagonists, but with the recently developed, selective, non-peptide and stable NPY antagonists it has now become possible to study subtypes of this receptor family. For instance, it has become clear that the NPY Y1 receptor mediates most of the direct peripheral effects of NPY on vascular tone. These antagonists promise to stimulate NPY research and will likely unravel the true significance of NPY in cardiovascular control under physiological conditions as well as in pathophysiological states.

Increase in skeletal muscle performance during emotional stress in man

An emotional stress arising as a result of intense mental arithmetic causes (in most subjects) an increase in blood flow through resting forearm muscle by an average of 85%. Combination of voluntary sustained handgrip contraction with mental arithmetic has shown that the duration of contraction increases by an average of 46%. This effect appears only in subjects who display an increase in blood flow as a result of mental arithmetic. A rise in muscle performance is also observed during mental arithmetic when contraction of forearm muscle is caused by direct stimulation of the motor nerve in the upper arm. Intra-arterial injection of atropine sharply reduces both the increase in blood flow through the resting muscle and the increase in muscle performance associated with mental arithmetic. Control performance (without mental arithmetic) is not altered by administration of atropine. Analysis of blood flow during muscle contraction leads to the conclusion that an increase in muscle performance during emotional stress is not dependent on an increase in muscle blood flow. The data suggest that during emotional stress the sympathetic nervous system causes metabolic changes in skeletal muscles that lead to an increase in muscle performance when oxygen deficiency exists.

Biosynthesis of epinephrine and norepinephrine by sympathetic nerves and ganglia

It is generally believed by the neurophysiologists that the sympathetic neurohormone is norepinephrine and not epinephrine as originally supposed. This concept of norepinephrine as the sympathetic neurohormone has evolved from much impressive circumstantial evidence; however, it has not been demonstrated that the biosynthesis of norepinephrine takes place in the sympathetic nerves and ganglia. This paper shows, through the use of labeled precursors, that the sympathetic nerves and ganglia synthesize norepinephrine in a systematic sequence from tyrosine and that this synthesis apparently terminates with norepinephrine rather than progressing to the formation of epinephrine.