TY - JOUR
T1 - Heat acclimation and hypohydration in aged rats
T2 - The involvement of adrenergic pathways in thermal-induced vasomotor responses in the portal circulation
AU - Shochina, Mara
AU - Haddad, Walid
AU - Meiri, Uri
AU - Horowitz, Michal
PY - 1996/10
Y1 - 1996/10
N2 - 1. The beneficial effects of heat acclimation on thermal induced vasomotor responses of hypohydrated aged rats were assessed by measuring the isometric tension of aortic and portal rings of old and young rats under heat acclimation and hypohydration in response to α-adrenergic (α-AR) and β- adrenergic (β-AR) stimulation (phenylephrine 10-9-10-2 mM and isoprenaline 10-9-10-4 respectively). In parallel, portal blood flow (PBF), which drains the splanchnic vasculature, was measured in conscious rats, before and during heat stress (42°C). 2. In the aorta, heat acclimation augmented phenylephrine (α-AR) induced tension, to a great extent in the older rats. Hypohydration increased α-AR sensitivity in all experimental groups. Acclimation and aging brought about decreased responsiveness in isoprenaline induced relaxation (β-AR) in both the aorta and the portal vein. Hypohydration increased β-AR responsiveness in the portal vein of OR, acclimated and acclimated-hypohydrated rats. 3. Normothermic euhydrated resting PBF was similar for young and old rats. Hypohydration decreased resting PBF. Upon heat stress, thermal induced vasoconstriction in hypohydrated YR and OR occurred earlier than in the euhydrated groups and was more pronounced. The latter responses were attenuated in the old rats. 4. Taken together, these results imply that chronic environmental stressors such as heat acclimation and hypohydration produce selective alterations in AR responsiveness of the vasculature in both young and old rats. Consequently, thermoregulatory vasomotor mediated mechanisms, as exhibited in this study in PBF, may differ in their responsiveness in these two age groups.
AB - 1. The beneficial effects of heat acclimation on thermal induced vasomotor responses of hypohydrated aged rats were assessed by measuring the isometric tension of aortic and portal rings of old and young rats under heat acclimation and hypohydration in response to α-adrenergic (α-AR) and β- adrenergic (β-AR) stimulation (phenylephrine 10-9-10-2 mM and isoprenaline 10-9-10-4 respectively). In parallel, portal blood flow (PBF), which drains the splanchnic vasculature, was measured in conscious rats, before and during heat stress (42°C). 2. In the aorta, heat acclimation augmented phenylephrine (α-AR) induced tension, to a great extent in the older rats. Hypohydration increased α-AR sensitivity in all experimental groups. Acclimation and aging brought about decreased responsiveness in isoprenaline induced relaxation (β-AR) in both the aorta and the portal vein. Hypohydration increased β-AR responsiveness in the portal vein of OR, acclimated and acclimated-hypohydrated rats. 3. Normothermic euhydrated resting PBF was similar for young and old rats. Hypohydration decreased resting PBF. Upon heat stress, thermal induced vasoconstriction in hypohydrated YR and OR occurred earlier than in the euhydrated groups and was more pronounced. The latter responses were attenuated in the old rats. 4. Taken together, these results imply that chronic environmental stressors such as heat acclimation and hypohydration produce selective alterations in AR responsiveness of the vasculature in both young and old rats. Consequently, thermoregulatory vasomotor mediated mechanisms, as exhibited in this study in PBF, may differ in their responsiveness in these two age groups.
UR - http://www.scopus.com/inward/record.url?scp=0030268343&partnerID=8YFLogxK
U2 - 10.1016/S0306-4565(96)00012-5
DO - 10.1016/S0306-4565(96)00012-5
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AN - SCOPUS:0030268343
SN - 0306-4565
VL - 21
SP - 289
EP - 295
JO - Journal of Thermal Biology
JF - Journal of Thermal Biology
IS - 5-6
ER -