Segments of thoracic aorta (DTA), tail artery (TA), and mesenteric artery branches (MAB) were obtained from male Fischer 344 rats at ages of 1, 2, 6, 12, 24, and 30 mo and were used to determine the effects of aging on agonist-activated 86Rb (and 42K) efflux. At all three arterial sites, basal efflux decreased during development (1-6 mo), but no further changes were observed with aging (6-30 mo). The initial efflux response to 10 microM norepinephrine (NE) in the presence of 1 microM propranolol exhibited either no change (DTA) or an increase (TA and MAB) during development (1-6 mo), but all three sites showed a large decrease during aging (6-30 mo). Changes in the steady-state response to NE paralleled changes in the basal efflux at all ages and arterial sites. The initial efflux response to 75 mM K+-physiological salt solution (PSS) for the DTA in the presence of 1 microM phentolamine and 1 microM propranolol decreased during development followed by an increase during aging, whereas for the TA and MAB, there were no significant changes with age. The steady-state efflux response to K+ decreased during development at all three sites but was increased only for the DTA during aging. The steady-state efflux response to K+ was not altered for the TA and MAB during aging. Efflux responses using 42K were qualitatively similar, but rate constants were quantitatively larger than those with 86Rb at all three arterial sites and at all ages.(ABSTRACT TRUNCATED AT 250 WORDS)
DELAY DISCOUNTING IN LEWIS AND FISCHER 344 RATS: STEADY-STATE AND RAPID-DETERMINATION ADJUSTING-AMOUNT PROCEDURES
