Our aim was to study the presence of noradrenergic nerves and to characterize the a-adrenergic receptors involved in the contractions to electrical field stimulation and to a-adrenergic agonists of the horse penile deep dorsal vein. Noradrenergic fibres were visualized by immunohistochemistry using an antibody against dopamine-beta-hydroxylase (DBH). For functional studies, the responses of the venous rings to electrical field stimulation and to a-adrenergic agonists (noradrenaline, phenylephrine and BHT 920) were studied in the absence and the presence of noradrenergic transmission-and neuronal sodium channel-blockers (guanethidine and tetrodotoxin, respectively) and of a 1 -and a 2 -adrenergic antagonists (prazosin and rauwolscine, respectively). DBHimmunoreactive fibres were present in the adventitia and in the media layer of the venous rings. Electrical field stimulation (0.5-32 Hz) caused frequency-dependent contractions that were abolished by guanethidine (10 À6 M) and tetrodotoxin (10 À6 M) and reduced by prazosin (10 À9 -10 À7 M) and rauwolscine (3 Â 10 À8 -3 Â 10 À7 M). Noradrenaline, phenylephrine and BHT 920 induced equipotent contractions of the rings. Prazosin and rauwolscine competitively antagonized the contractions to phenylephrine and BHT 920, respectively. In conclusion, DBH-immunoreactive nerve fibres are present in the horse penile dorsal vein. Both transmural nerve stimulation and a-adrenergic agonists induce contraction of the venous rings through a heterogeneous population of a 1 -and a 2 -adrenoceptors.
In 1921, Otto Loewi published an experimental study that gave rise to the birth of the chemical theory of nerve transmission, according to which, the nerve current causes, at the end of nerve fibers, the release of a chemical substance called a neurotransmitter. For his discoveries related to the chemical neurotransmission of nerve impulses, Loewi received the Nobel Prize in Physiology or Medicine in 1936.
Urinary incontinence represents a serious social, medical and economic problem, which suffers a progressive increase, due to the increase in life expectancy that social, health and cultural advances have achieved. It is estimated that in the world there are approximately two hundred million people in urinary incontinence with a great economic impact of great importance that can exceed the coverage forecasts of the different systems of health care services. Our group from the Department of Physiology of the UCM has been studying the physiology of the lower urinary tract (LUT) for several years in order to determine the neurotransmitters and receptors that regulate these structures. This greater knowledge of the Physiology and Pathophysiology of the LUT has allowed these dysfunctions to be corrected with pharmacological methods compared to the traditional alternative of surgery. Keywords: micturition; urinary incontinence; chemical neurotransmission; neurotransmitters; receptors
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