Analysis of the inhibition of the ACTH release by hypothalamic implants of atropine

The effect of anterior hypothalamic atropine implants on the secretion of corticotrophin in the rat, as indicated by the corticosteroid production by adrenal glands incubated in vitro and/or by the plasma corticosterone concentration, was studied. It was found that atropine implants markedly inhibit the adrenocortical responses evoked by all the stress stimuli tested, except for that to a CRF preparation. The onset of the blockade was very fast; the duration of the inhibition lasted for about 2 hr. Smaller amounts of atropine (2 x 15 μg) were also effective when implanted bilaterally into the anterior hypothalamic region. It is concluded that cholinergic synapses in the hypothalamus may be involved in the activation of the pituitary adrenal system after stressful stimuli.