Fig. 28.Schematic representation of the interactions between somatostatin (SRIH)-producing neurons in the hypothalamic periventricular nucleus (Pev) and growth hormone releasing hormone (GHRH)-producing neurons in the arcuate nucleus. Note that in addition to projections to the external zone of the median eminence, these neurons may also have reciprocal connections. Ghrelin (GHR) may also influence GH secretion by acting directly on somatotrophs or through stimulatory effects on GHRH neurons. AP = anterior pituitary, GH = growth hormone, IGF = insulin-like growth factor, ME = median eminence, PP = posterior pituitary. R-SRIH and R-GHRH correspond to receptors for the respective peptides. (Adapted from Epelbaum J: Intrahypothalamic neurohormonal interactions in the control of growth hormone secretion. Functional Anatomy of the Neuroendocrine Hypothalamus, Wiley, Chichester, 1992; pp 54-68.)