The failure of L-prolyl-L-leucylglycinamide to inhibit the release of α-melanocyte-stimulating hormone in the rat

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Abstract
The effect of L-prolyl-L-leucylglycinamide (PLG) on the release of melanocyte-stimulating hormone (melanotropin, MSH) from the rat pituitary gland was studied both in vitro and in vivo. Superfusion of neurointermediate lobes with medium containing PLG or PLG-acetate (dose range 1-1000 ng/ml) did not affect the spontaneous release of MSH as determined by radioimmunoassay or by bioassay. Also during static incubations of rat hemipituitaries, PLG (6.6-50 ng/ml) was without effect on .alpha.-MSH release. PLG administration (1-250 ng i.v.) to intact male and female rats and rats bearing lesions in the medio-basal hypothalamus did not induce a fall in serum .alpha.-MSH levels. PLG apparently does not affect the release of .alpha.-MSH from the rat intermediate lobe. It is unlikely that PLG mediates the inhibitory influence of the CNS on MSH release.