Effects of chronic nicotine administration and age on various neurotransmitters and associated enzymes in male Fischer-344 rats

Relationship of Urinary Serotonin Excretion to Cigarette Smoking and Respiratory Symptoms

The relationship of 2-h urinary excretion of serotonin and 5-hydroxyindoleacetic acid (5-HIAA) to cigarette smoking and respiratory symptoms was examined among 631 male participants in the Normative Aging Study (age range, 44 to 85 years). The amount of serotonin excreted in urine was inversely related to age (p less than 0.001). Mean 2-h excretion of serotonin varied from 8.01 micrograms for men 40 to 49 years of age to 5.84 micrograms for those 70 years of age or over. No clear relationship was evident between the amount of 5-HIAA excreted in urine and age. After adjustment for age, current smokers were found to excrete more serotonin (p less than 0.001) and 5-HIAA (p = 0.001) than never smokers. Former smokers did not differ significantly from never smokers in these respects. After adjustment for age and smoking status in a multivariate model, chronic cough was a significant predictor of serotonin excretion (p = 0.005); chronic cough was less predictive of 5-HIAA excretion (p = 0.07). Other respiratory symptoms were unrelated to urinary excretion of serotonin and 5-HIAA. The mechanisms underlying the observed relationships of urinary serotonin and 5-HIAA excretion to smoking and to chronic cough and their potential relevance to chronic bronchitis remain to be determined.

Effects of age on the adrenergic cardiac neuroeffector junction

Although it is clear that adrenergic nervous system control of cardiac function decreases with age and that the effector organ fails to adjust to this decreased control, it is not completely evident which of the many mechanisms operant at the adrenergic-cardiac neuroeffector junction contribute to this state. Prejunctionally, it appears that norepinephrine content decreases with age and that adrenergic axonal degeneration occurs. Also, evidence is available to suggest that modulation by prejunctional alpha adrenergic receptors of norepinephrine release is altered with increasing age, as is neuronal uptake of norepinephrine. Postjunctionally, it appears that beta-adrenergic receptor sensitivity to agonists undergoes age-related alterations, and possibly post receptor mechanisms involved in receptor-response coupling. Other mechanisms, such as those involved in transmitter uptake into extraneuronal sites, adrenergic neuronal responsiveness to stimulation, transmitter release and turnover, calcium and prejunctional receptor modulation of transmitter release, postjunctional receptor development of supersensitivity or subsensitivity, need further elucidation in order to have an understanding of the factors that contribute to the breakdown of homeostatic mechanisms that regulate the heart.

Pharmacokinetics of nicotine in rats after multiple-cigarette smoke exposure

The pharmacokinetics of nicotine and its major metabolites was evaluated in male rats after multiple-cigarette smoke exposure. A smoke-exposure apparatus was used to deliver cigarette smoke to the exposure chamber. The rats were exposed to smoke from a single cigarette every 8 hr for 14 days and to the smoke of a cigarette spiked with radiolabeled nicotine on the 15th day. Blood and urine samples were collected at timed intervals during the 10-min smoke-exposure period of the last cigarette and up to 48 hr thereafter. Nicotine, cotinine, and other polar metabolites were separated by thin-layer chromatography and quantified by liquid scintillation counting. The data were analyzed by computer fitting, and the derived pharmacokinetic parameters were compared to those observed after a single iv injection of nicotine and after a single-cigarette smoke exposure. The results indicated that the amount of nicotine absorbed from multiple-cigarette smoke was approximately 10-fold greater than that absorbed from a single cigarette. Also, unlike the single-cigarette smoke exposure experiment, nicotine plasma levels did not decay monotonically but increased after the 5th hr, and high plasma concentrations persisted for 30 hr. The rate and extent of the formation of cotinine, the major metabolite of nicotine, were decreased as compared with their values following a single-cigarette smoke exposure. It was concluded that nicotine or a constituent of tobacco smoke inhibits the formation of cotinine and may affect the biotransformation of other metabolites. Urinary excretion tended to support the conclusions that the pharmacokinetic parameters of nicotine and its metabolites were altered upon multiple as compared to single dose exposure.

Changes in the biochemistry of the rat heart with increasing age

Effects of increasing age on biochemical parameters of rat hearts have been summarized, as far as possible, in a descriptive, qualitative manner. Where available, the strain, age, and sex of rats have been included. Due to a lack of uniformity in expressing chemical components and enzyme activities found in rat hearts, it is inappropriate in a review of this type to advance hypotheses regarding the nature of biochemical changes that may be contributing to or be the results of aging processes.