Abstract
The anterior pituitary is an endocrine interface between the brain and peripheral organs. This gland secretes hormones periodically, under the control of hypothalamic factors episodically released into the portal blood vessels of medium eminence. However, the hypothalamic influence does not fully explain the harmonisation of secretory activities of the distinct endocrine cell types scattered throughout the tissue. This indicates that a large-scale communication system exists within the anterior pituitary. We provide evidence for a new intrapituitary communication system by which information is rapidly transferred via the network of non-endocrine folliculostellate (FS) cells. In acute rat pituitary slices, preparation that keeps intact the tissue architecture, we discovered the hitherto unknown membrane excitability of FS cells. Excitability is one of the means to trigger long-range calcium waves in FS cells, which propagate to other FS cells by signaling through gap-junctions and can relay information between opposite regions of the gland. We also studied the in situ release by FS cells of interleukin-6, a cytokine known to stimulate the release of all pituitary hormones. PACAP stimulated IL-6 release from acute pituitary slices, most likely by acting at the IL-6 gene level. Strikingly, alteration of gap junction coupling alter the pattern of PACAP-induced IL-6 release. Because FS cells respond to central and peripheral stimuli and dialogue with endocrine cells, the form of large-scale intrapituitary communication described here may provide an efficient mechanism that orchestrates anterior pituitary functioning in response to physiological needs.