Circulating atrial natriuretic factor activates vagal afferent inputs to paraventriculo-spinal neurones in the rat.

In urethane-anaesthetised, paralysed and artificially ventilated rats (300-350 g b.wt.), i.v. bolus injection of 3-5 micrograms atrial natriuretic factor (ANF) inhibited the activity of 5/8 (62.5%) antidromically identified spinally projecting neurones in the parvocellular portion of the hypothalamic paraventricular nucleus for periods of 6-40 min, mean 24 min. In contrast a much lower dose of ANF (250 ng) evoked a strong excitatory response in 37.5% of cells tested and either a weak inhibition or no effect on the remainder. Both inhibitory and excitatory effects were absent in bilaterally vagotomised animals. The results are discussed in relation to the role of circulating ANF in activating vagal afferent inputs to the paraventricular nucleus during volume loading.