SOME OBSERVATIONS ON THE PHARMACOLOGY OF ALPHA-METHYLDOPA

alpha-Methyldopa in high concentrations impaired the responses of rabbit isolated ileum and guinea-pig isolated vas deferens to stimulation of the sympathetic nerves and to noradrenaline, but these preparations taken from animals previously treated with alpha-methyldopa showed no sign of impairment. Contractions of the cat nictitating membrane were reduced but not abolished by alpha-methyldopa. In cats, dogs and rats, pressor responses to noradrenaline were usually slightly increased by alpha-methyldopa. Pressor responses to tyramine were not affected consistently. alpha-Methyldopa, alpha-methyldopamine and alpha-methylnoradrenaline behaved like dopa, dopamine and noradrenaline respectively in restoring the responses of tissues from reserpine-treated animals to stimulation of the sympathetic nerves to the rabbit ileum, the guinea-pig vas deferens and the cat nictitating membrane and in restoring responses to tyramine of the cat blood pressure and nictitating membrane, and the rat blood pressure. The potency of alpha-methylnoradrenaline relative to noradrenaline ranged from one-half to one-ninth on various preparations. The results are discussed in relation to the antihypertensive action of alpha-methyldopa.

Contraindications to vasoconstrictors in dentistry: Part III. Pharmacologic interactions

This article discusses the relative contraindications to the use of vasoconstrictor in patients currently medicated with tricyclic antidepressants, monoamine oxidase inhibitors, phenothiazines and beta-blockers. It reviews drug interactions and emphasizes potential detrimental systemic effects that epinephrine contained in local anesthetics can have when administered concomitantly with these drugs. Finally, special considerations are expressed concerning patients who abuse illicit drugs such as cocaine.

Platelet alpha 2-adrenergic receptor responsiveness is increased in elderly men but not in elderly women

We ascertained platelet alpha 2-adrenergic receptor responsiveness in healthy young and elderly men and women by determining the minimum concentration of methylnorepinephrine, a selective alpha 2-adrenergic receptor agonist, required to initiate the primary and secondary aggregation response in platelet-rich plasma. We observed that platelets from elderly men required a smaller concentration of methylnorepinephrine to stimulate primary aggregation than did platelets obtained from young men. However, the concentration of alpha 2-adrenergic receptor agonist to trigger the secondary aggregation response did not vary with age. There was no difference in the responsiveness of platelets from young and elderly women for either the primary or secondary aggregation response. We conclude that platelet alpha 2-adrenergic receptor responsiveness is increased with age rather than decreased, as predicted from some studies of the density of platelet alpha 2-adrenergic receptors and their coupling to adenylyl cyclase. Furthermore, the increase in alpha 2-adrenergic receptor responsiveness is gender specific.

Contraindications to vasoconstrictors in dentistry: Part I. Cardiovascular diseases

This article reviews the main contraindications of vasoconstrictors in cardiac patients, notably unstable angina, recent myocardial infarction, recent coronary artery bypass surgery, refractory arrhythmias, untreated or uncontrolled hypertension, and untreated or uncontrolled congestive heart failure. Extensive survey of the literature has been completed, giving specific guidelines for a rational use of vasoconstrictors in this category of medically compromised patients.

An evaluation of 4% prilocaine with 1:200,000 epinephrine and 2% mepivacaine with 1:20,000 levonordefrin compared with 2% lidocaine with:100,000 epinephrine for inferior alveolar nerve block

The purpose of this study was to measure the degree of anesthesia obtained with 4% prilocaine with 1:200,000 epinephrine and 2% mepivacaine with 1:20,000 levonordefrin compared with 2% lidocaine with 1:100,000 epinephrine for inferior alveolar nerve block. Using a repeated measures design, 30 subjects randomly received an inferior alveolar injection using masked cartridges of each solution at three successive appointments. The first molar, first premolar, lateral incisor, and contralateral canine (control) were blindly tested with an Analytic Technology pulp tester at 3-min cycles for 50 min. Anesthetic success was defined as no subject response to the maximum output of the pulp tester (80 reading) within 16 min and maintenance of this reading for the remainder of the testing period.Although subjects felt numb subjectively, anesthetic success as defined here occurred in 46% to 57% of the molars, in 50% to 57% of the premolars, and in 21% to 36% of the lateral incisors. No statistically significant differences in onset, success, failure, or incidence were found among the solutions. We conclude that the three preparations are equivalent for inferior alveolar nerve block of 50-min duration.

Prefrontal cortex: dense dopaminergic input in the newborn rat

Using a recently introduced modification of the aluminum-formaldehyde histofluorescence method, in combination with exogeneous administration of alpha-methylnoradrenaline and biochemical analyses, a remarkably advanced development of the dopaminergic and noradrenergic afferent to the frontal lobe has been demonstrated in neonatal rat. At birth, the density and general distributional pattern of the catecholamine innervation was similar to that found in the fully developed prefrontal cortex. The previously not recognized, early and extensive maturation of the mesocortical dopamine projection suggests a functional role of dopamine already in the early postnatal period.

Characterization of the monoaminergic innervation of immature rat neocortex: a histofluorescence analysis

In the neocortex of 6-day-old rat, abundant axon terminals which exhibit specific catecholamine fluorescence are found in all regions and throughout all cortical layers. The overall density of axons in 6-day-old cortex is similar to the density in the adult cortex. In immature cortex, there are two distinct fluorescent plexuses, both presumably noradrenergic, one in the molecular layer and another in the lower half of the cortex. The superficial plexus is composed primarily of horizontal fibers, and the deep plexus of a dense feltwork of obliquely oriented fibers suggestive of a terminal field. The cortical plate itself is traversed by a few vertical processes. Following lesions of the midbrain tegmentum no fluorescent axons are seen in cortex, providing evidence that the fluorescent axons in cortex arise from brain stem neurons. The deep and superficial plexuses can be differentially visualized depending on the histochemical techniques employed and on pharmacological treatment, such as loading with a monoamine congener. Both deep and superficial axons are shown to contain endogenous catecholamines but those fibers in the deep plexus are filled to far less than their maximum capacity. The pharmaco-histochemical differences between axons in the two plexuses suggest that there may exist two distinct catecholaminergic projections to lateral neocortex. The demonstration of an extensive cortical monoamine innervation early in ontogeny supports the possibility that monoamine neurons play an important role in information processing and/or developmental interactions in the immature brain.

A catecholaminergic neuron connecting the first two optic neuropiles (lamina ganglionaris and medulla externa) of the crayfish pacifastacus leniusculus

The crustacean optic neuropiles, the lamina ganglionaris and especially the medulla externa, show a specific pattern of green fluorescence with the fluorescence histochemical method of Falck-Hillarp. Normally, only the terminals and the cell bodies fluoresce, but in reserpine-treated animals exogenous catecholamines are taken up by the whole adrenergic neuron and are thus visualized as a whole. Incubating crayfish optic neuropiles in dopamine or alpha-methylnoradrenaline after reserpine treatment demonstrated a tangential neuron connecting the lamina and the medulla externa. The morphology of this tangential neuron differs from the two types of tangential neurons, Tan1 and Tan2, previously characterized with Golgi techniques. The catecholaminergic neuron thus constitutes, a third tangential neuron type.

Adrenergic innervation of the mouse heart revealed at an early stage using alpha-methylnoradrenaline

The development of noradrenergic innervation was studied in the mouse heart using fluorescence histochemistry. Following incubation of hearts with alpha-methylnoradrenaline fluorescent nerve fibres were seen as early as 13 days in utero. It is suggested that the neuronal uptake mechanism for noradrenaline is functional at an early stage.