Interaction With Age And Temperature Of The Responses To a-Adrenergic Receptor Agonists And Antagonists In The Rabbit And Guinea-pig Aortas

In this in vitro study, the effects of maturation and hypothermia on the contractile responses to phenylephrine (PHE) and clonidine (CLO) and on the inhibition of these responses by prazosin (PRA) or yohimbine (YOH) on young (2-3 months old) and mature (11-12 months old) rab-bit and guinea-pig aortas have been in-vestigated. The cumulative addition of PHE and CLO were dose-dependently contracted these tissues and the dose-dependent relaxations were obtained with the cumulative addition of PRA or YOH on maximum contractions. At 37 °C. as the pa2 values of PHE and CLO were significantly greater in the aortas from mature rabbits and guinea-pigs than from young groups, no age-related changes in the IC50 and 11/2 values of PRA and YOH were detected in both aortas. At 28 °C, the pD2 values of agonists, and the IC50 and t11, values of antagonists were significantly lower than of 37 °C. Furthermore, at 37 °C, as its expected, the values for PRA against PHE were significantly greater than the values obtained with YOH against CLO on aortas from mature rabbits and guinea-pigs. In conclusion, as it's seen in many other tissues, in in vitro conditions on rabbit and guinea-pig aortas. the responses to a-adrenergic receptor agonists were altered with age and temperature although the responses to antagonists were altered with the temperature only.