A simple model to characterize sympathetic and parasympathetic effects on heart rate (R) was tested during rest in 10 nonathletes and 8 world-class oarsmen. The model states that R = mnR0, where R0 is the intrinsic cardiac rate, and m and n depend only on sympathetic and parasympathetic activity, respectively. The multipliers, m and n, were determined by dual pharmacological blockade in two sessions under similar conditions, but in one session propranolol and in the other atropine was given first. In agreement with the model, when corrections were made for atropine-induced blood pressure changes, m and n did not depend on which blocking agent was administered first. In athletes the control heart rate [55 +/- 3.3 (SD) beats/min] and R0 (81 +/- 8.3 beats/min) were lower than in nonathletes (62 +/- 6.0, P less than 0.01 and 102 +/- 11, P less than 0.001, respectively). The sympathetic multiplier, m, was similar (1.18 +/- 0.06 vs. 1.20 +/- 0.05, P greater than 0.4) in the two groups, but n, the parasympathetic multiplier, was closer to 1 in the athletes (0.57 +/- 0.03 vs. 0.51 +/- 0.05, P less than 0.01). We conclude that the model is suitable for the quantitative study of sympathetic/parasympathetic heart rate control in humans, and that the lower resting heart rate in oarsmen is solely due to a reduction in intrinsic cardiac rate, and not to an increase in parasympathetic tone.
1. The properties of beta-adrenoceptors mediating vascular relaxation in rat isolated carotid artery were investigated. Ring segments of arteries were preconstricted with the thromboxane A2 receptor agonist U-46619 and relaxation to beta-adrenoceptor agonists determined. 2. Isoprenaline produced a concentration-dependent relaxation of U-44619-constricted arteries. The concentration-response curve (CRC) to isoprenaline was shifted to the right by propranolol (1 microM) although the shift was less (105 fold; pA2, 8.02) than would be expected for an effect of isoprenaline at classical beta-adrenoceptors (300-1000 fold; pA2, 8.5-9). L-NAME (100 microM) significantly reduced responses to isoprenaline, lowering the slope of the CRC and reducing the maximum response. 3. The selective beta3-adrenoceptor agonists, BRL 37344 and ZD2079, also produced concentration-dependent relaxation of the arteries. L-NAME (100 microM) shifted the BRL 37344 CRC to the right 15 fold with no reduction in the slope or maximum response. L-NAME (100 microM) had no significant effect on the ZD2079 CRC. 4. In conclusion, relaxation to isoprenaline in rat carotid artery is inhibited by propranolol in a manner suggesting a mixed population of classical (beta1-/beta2-) and atypical (beta3-) adrenoceptors. The presence of beta3-adrenoceptors was confirmed by the relaxant effects of the selective beta3-adrenoceptor agonists BRL 37344 and ZD2079. L-NAME attenuated responses to both isoprenaline and the beta3-adrenoceptor agonist BRL 37344, suggesting a role for endothelial release of nitric oxide in beta-adrenoceptor mediated relaxation. However, the relaxant effect of BRL 37344 was attenuated by L-NAME to a lesser extent than that of isoprenaline. In addition, L-NAME had no effect on relaxation induced by ZD2079. These results suggest that there may be a differential contribution of endothelium to classical beta-and beta3-adrenoceptor-mediated effects, with endothelium contributing less to beta3-adrenoceptor-mediated relaxation.
Described as the greatest health crisis to face mankind in the modern era, the threat of HIV and AIDS in the workforce provides important challenges for consumer businesses that seek to balance divergent public opinions with the need to provide adequately for the health care requirements of their workforce. This research, based upon a survey that included 42 of the UK's largest retailers, identifies the many issues surrounding the development of a credible business response to this health issue. The research findings suggest that many retailers have taken cognisance of customer feeling in their development of policies in this area and that in some instances the development of HWAIDS policies in respect of staff has had more to do with politically correct posturizing than a commitment to the welfare of staff.
Examines UK retailers' attitudes towards employee welfare in general, and the development and implementation of policies in respect of staff with HIV/AIDS in particular. From the research results, provides a valuable insight into retailer motivation in respect of staff welfare provision and the methods adopted by retailers in the development of welfare policy; identifies the need to ensure that a credible support strategy exists in order that welfare policies, such as those related to HIV/AIDS, can be implemented effectively. Indicates that the management of HIV/AIDS within the retail sector is complicated further by the threat of criminal attack on retail staff and the potential for negative consumer reaction to policy decisions, and concludes by suggesting that the development of a considered response to HIV/AIDS is one which UK retailers cannot afford to ignore.
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