α-MSH and MIF-I effects on catecholamine levels and synthesis in various rat brain areas

Attempts were made to find a biochemical correlate with previously observed behavioral alterations after administration of α-melanocyte-stimulating hormone (MSH) and MSH release-inhibiting factor (MIF-I). Brains of intact and hypophysectomized (hypox) rats were analyzed for endogenous catecholamine levels and the disappearance rate of endogenous norepinephrine (NE) after treatment with the tyrosine hydroxylase inhibitor α-methyl-para-tyrosine (AMPT). The studies undertaken show the following: (1) After the injection of MSH (100 μg/kg IP daily × 3) and AMPT, samples in different groups of intact and hypox rats were taken at 0, 1, 2, 4 and 6 hrs in 7 different brain areas. In the mid-brain area for the intact group of rats, the rate of disappearance of NE was faster and for the hypox rats it was slower than the rate for control rats not treated with the peptides. NE levels in the same area at time 0 were 11 percent lower than controls in hypox rats and unchanged in unoperated animals. (2) After the injection of MIF-I (20 mg/kg IP daily ×3) in similar experiments as with MSH, a reduced rate ( p