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In addition, cerebrovascular CO2 reactivity is unchanged with increasing age in men (Kastrup et al. 1998). Although cerebrovascular CO2 reactivity has been shown to decline significantly with age in women, in the present study women subjects were [http://www.selleckchem.com/products/pd-1-pd-l1-inhibitor-2.html learn more] only four of twelve. Thus, on balance the observed differences in CCP associated with either ageing or exercise do not seem to be related to changes in the arterial partial pressure of CO2. An alternative explanation for the greater exercise-induced CCP response in older subjects is the greater pressor response to exercise observed in this group. Changes in CCP during exercise have previously been shown to be unrelated to increases in arterial blood pressure in young individuals (Ogoh et al. 2010), and likewise in the present study the CCP and MAP responses to leg cycling were not significantly related in the young subjects. However, in contrast, exercise-induced increases in MAP and CCP [http://www.selleckchem.com/products/cobimetinib-gdc-0973-rg7420.html Cobimetinib] were found to be significantly related in older individuals. In addition, in the older subjects the increases in MAP and CCP from rest were greater than in younger subjects during both the low- and the moderate-intensity steady-state cycling bouts, while MCA Vmean responses were similar. Animal investigations have provided strong evidence to suggest that cerebral vasoconstriction protects cerebral vessels during severe hypertension (Bill & Linder, 1976; [http://en.wikipedia.org/wiki/ALG1 ALG1] Heistad et al. 1978). Thus, it is plausible that the greater increases in CCP we observed in older subjects served to protect the blood�Cbrain barrier from the higher blood pressure responses evoked by dynamic exercise in this group. However, it should be noted that an exaggerated increase in cerebral vascular tone may limit increases in cerebral blood flow during exercise, thus potentially limiting cerebral oxygen delivery and precipitating the development of fatigue during vigorous or prolonged exercise in the elderly (Hashimoto et al. 1999). Additional studies are warranted. In addition, the greater CCP during exercise may have implications during the immediate postexercise period when MAP is low (i.e. postexercise hypotension), when a high cerebral vascular tone may contribute to a reduced control of cerebral blood flow and even syncope in older individuals (Murrell et al. 2009). Age-related increases in peripheral vascular tone, either at rest or during exercise, have been associated with exaggerated sympathetic nerve activity (Sundl?f & Wallin, 1978; Ng et al. 1993; Davy et al. 1998) and blunted vasodilator responsiveness (Taddei et al. 2001). In addition, the metabolic modulation of sympathetic vasoconstrictor tone has been shown to be impaired in the vascular beds in contracting muscle of elderly individuals (Fadel et al. 2004; Dinenno et al. 2005).