ABSTRACT
The release of MSH from the pars intermedia or the anterior pituitary is controlled by MSH-releasing hormone (MRH), MSH release-inhibiting hormone (MRIH), and dopamine (Ch. 7). The ring structure of oxytocin, which is produced by paraventricular nuclei in the hypothalamus and stored in the neurohypophysis, may be the source of MRH, and the tripeptide side chain the source of MRIH (Part D). There does not appear to be any direct feedback effect on MSH release from target tissues, since stimulation of melanocytes by -MSH does not release any possible feedback candidates into the circulation. Perhaps the strong two-or three-way control of MSH release by the hypothalamus precludes a biologic requirement for target tissue negative feedback.
