Dual Excitatory and Inhibitory Effects of Stimulation of Intrinsic Innervation of the Anterior Pituitary on Adrenocorticotropic Hormone Release in the Rat

Abstract

The gland cells of the mammalian anterior pituitary are innervated by substantial amounts of nerve fibres, and there is evidence that the nerve fibres are functionally active. In the rat, the nerve fibres make typical excitatory synapses with corticotropes. The physiological significance of this synaptic relationship was investigated in the present study. The anterior pituitary of the rat was sliced and stimulated with electrical field in a chamber. The perfusate was continuously collected and immunoradioassayed for adrenocorticotropic hormone (ACTH). When the gland slices were stimulated at a high frequency of 10 Hz, there was a significant inhibition of ACTH secretion. Stimulation at a low frequency of 2 Hz resulted in a quick and transient excitation of ACTH release. The results indicate that stimulation of the nerve fibres in the anterior pituitary has dual excitatory and inhibitory effects on ACTH secretion.

Excitatory and inhibitory effects of prolactin release activated by nerve stimulation in rat anterior pituitary

“…Reports of Gao LZ et al have strongly implied the existence of direct neural regulation on ACTH release [22,23]. The present study indicates that EFS of the nerve fibers in the anterior pituitary of the rat have excitatory and inhibitory effects on prolactin secretion.…”

“…Although the release of prolactin occurred as quickly as in the case of ACTH, it followed a much gentler slope and lasted longer. When stimulated for 10 min, the enhancing effect on prolactin release lasted for as long as 30 min, whereas for ACTH, there was only sharp peak of release even though the stimulation continued for 10 min [22]. The reason of this difference remains to be elucidated.…”

“…Based on our previous experience [22], square waves of 0.5 ms and 20 mA were used. 2 Hz and 10 Hz were selected for low and high frequency, respectively, which may induce different transmitter releasing [20,21].…”

“…Our subsequent study indeed proved that when the nerve fibers in the anterior pituitary were stimulated at a low frequency of 2 Hz, which is known to induce release of classical transmitters from the small clear synaptic vesicles [20,21], there appeared an almost immediate surge of ACTH release of two minutes (min). However, when stimulated at 10 Hz, a frequency acknowledged to induce exocytosis of the large dense-core synaptic vesicles, which contain mainly neuropeptides [20,21]; there appeared a slower and longer gentle curve of ACTH inhibition [22,23]. …”