Studies of the penetration of the blood brain barrier by atrial natriuretic factor

The atrial natriuretic factors (ANF) have been detected in various areas of the brain. To determine whether circulating blood borne ANF could contribute to the ANF content in the central nervous systems we examined the ability of ANF-99-126 or ANF-102-126 to penetrate the blood brain barrier. Carotid artery injections of 3H] inulin with 125I] ANF in anesthetized rabbits resulted in a comparably minimal brain uptake index (BUI) for each labeled substance as measured in cerebral cortex extracts. Injection of 3H] HOH and 125I] ANF resulted in a mean BUI in cortex of 4.9 +/- .6 (SEM)% for ANF relative to triated water; this low uptake was not significantly saturable. The BUI ratio for ANF/HOH in olfactory bulb was somewhat higher though still low, at 7.0 +/- 9%, possibly reflecting the high density of ANF receptors in this structure. Infusion of 125I] ANF into the carotid artery of anesthetized rabbits resulted in little radioactivity being detected in the cerebrospinal fluid. Infusion of unlabeled ANF, which raised plasma levels as high as 26.3 ng/ml, resulted in little change in CSF levels. Our results demonstrate that the uptake of ANF into the brain is minimal and supports the idea that local synthesis of ANF predominantly accounts for the brain pool of this peptide.