Mammalian FMRF-NH2-like peptide in rat pituitary: decrease by osmotic stimulus.

Previous studies with the Brattleboro rat suggested a possible interaction at the pituitary level between AVP and the neuropeptide, F-8-F-NH2. In order to test this hypothesis, we studied the effect of various osmotic stimuli on neurohypophyseal F-8-F-NH2. In rats drinking 2% NaCl solution for two days, neural lobe AVP and F-8-F-NH2 levels were equally reduced by 87%. After maximal depletion, pituitary levels of F-8-F-NH2 and AVP rebounded in parallel when normal drinking water was reintroduced. Pituitary stalk transection depleted neurohypophyseal F-8-F-NH2. The results of this study suggest that neurohypophyseal F-8-F-NH2 originates from the hypothalamus and, furthermore, is coreleased along with AVP in response to hyperosmotic stimuli.