Critical review: nicotine for the fetus, the infant and the adolescent?

The recent expansion of Nicotine Replacement Therapy to pregnant women and children ignores the fact that nicotine impairs, disrupts, duplicates and/or interacts with essential physiological functions and is involved in tobacco-related carcinogenesis. The main concerns in the present context are its fetotoxicity and neuroteratogenicity that can cause cognitive, affective and behavioral disorders in children born to mothers exposed to nicotine during pregnancy, and the detrimental effects of nicotine on the growing organism. Hence, the use of nicotine, whose efficacy in treating nicotine addiction is controversial even in adults, must be strictly avoided in pregnancy, breastfeeding, childhood and adolescence.

The importance of sensory nerve endings as sites of drug action

The role that sensory nerve endings can play in drug action and the strategy used for its experimental analysis and proof is first exemplified by three effects of nicotine which are seen when the lowest effective doses of the drug are given intravenously in the cat: (1) a vasopressor effect due to arterial chemoreceptor stimulation; (2) a triad of bradycardia, hypotension and apnea, and (3) a depressant effect upon somatic motor activity, both of which are traced to vagal afferent endings in the pulmonary circulation. While receptors in the lung are responsible at least for the initial phase of the reflex responses listed in (2) and (3), sensory endings in heart, aorta, and carotid sinus region may be recruited into action as the drug reaches them. Several of these reflex effects can also be elicited by other sensory stimulant agents such as phenyldiguanide, 5-hydroxytryptamine, and veratrum alkaloids. In the second part, a general outline is given of what may be classified as 'Afferent Pharmacology', dealing with drug action upon sensory receptors and with the resulting remote drug effects. The action upon sensory receptors can either be a direct one ('primary' drug effect) consisting of stimulation, sensitization, desensitization, depression or combinations thereof, or an indirect ('secondary') effect brought about by a variety of drug-induced changes in the tissues surrounding the receptors. Depending on the nature of the primary or secondary action, the remote drug effect can be either an initiation, modification or impairment of those reflexes which have their origin in the sensory endings acted upon. Indeed, the grossly observable pharmacological actions of 'afferent drugs' are generally those relating to the reflex response. To avoid blurring of the boundaries of afferent pharmacology, drugs acting on central synapses of reflex pathways, or on the elaborate efferent control system of afferent input, are not included. A discussion follows of the topics of investigation, the influence of experimental conditions and anesthesia, various approaches and methods, the physiological and pharmacological importance of inquiry in this area, and some of the therapeutic aspects. Finally, brief mention is made of certain features and problems which appear to be characteristic of afferent pharmacology.

Nicotine-induced reflex depression of alpha motoneuron activity in the absence of fusimotor-spindle feedback

The effects of nicotine on the stretch reflex and on electrically induced monosynaptic and cutaneous polysynaptic reflex responses at a lumbosacral level were studied in lightly anesthetized (chloralose-urethane) cats in which the regional fusimotor-spindle loops had been interrupted by ventral rhizotomy. Doses of 15-40 mug/kg injected into the superior vena cava or the right atrium produced depression of the reflex responses in extensor and flexor alpha motoneurons after latent periods of 1-3 sec, while gamma activity was initially accelerated. The early phase of this alpha depression was abolished by bilateral vagotomy. Sebacylcholine (a nicotinic agent) and acetylcholine also caused depression of evoked alpha activity in the absence of spindle feedback. It is concluded that nicotine activates a viscerosomatic reflex by exciting sensory receptors in the cardiopulmonary region and that alpha motor depression results independent of the changes in gamma activity. However, alpha depression with delayed onset can still be elicited by nicotine after vagotomy and Renshaw blockade, and this effect is also duplicated by sebacylcholine and abolished by hexamethonium. In the doses used, spindle or skin afferents were not excited by nicotine. Thus, two more mechanisms are described by which nicotine can depress alpha activity. Both are reflex in nature, one implicating vagal, the other nonvagal peripheral receptors.

Hazards smokers impose

Tobacco smoke is the single most important source of exposure for the nonsmoking population to harmful air pollution. Uptake, biological reaction, and associated pathology document the potential for serious health consequences, raise ethical and legal questions, and demand comprehensive legislative action.