No abstract

A modification of our previous radioimmunoassay (RIA) for α-melanocyte-stimulating hormone (α-MSH) is described that permits the measurement of circulating levels in the rat without the need for an extraction procedure. Using this method, serum and neurointermediate lobe () immunoreactive α-MSH levels were measured in rats after administration of haloperidol, 2-bromo α-ergocryptine (CB 154), and α-methyl-p-tyrosine (α-MPT). Haloperidol caused a rapid increase, α-MPT a slow increase, and CB 154 a rapid decrease in serum α-MSH. At the time intervals studied none of the drugs had any significant effect on α-MSH content. It was concluded from the results of the above drug treatments that modulation of dopaminergic neurotransmission both pre- and postsynaptically produces changes in serum immunoreactive α-MSH levels. This supports the suggestion that circulating α-MSH in the rat is under an inhibitory control by a catecholaminergic system.

No abstract

A sensitive and specific radioimmunoassay for alpha-melanocyte-stimulating hormone (alpha-MSH) was developed. Extracts of the neurointermediate lobe of the rat produced displacement curves which were parallel to those obtained with synthetic alpha-MSH. The mean immunoreactive alpha-MSH concentration in neurointermediate lobes from normal adult rats was 2768 +/- 200 (S.E.M.) ng/lobe. This accounted for approximately 78% of the MSH activity of the neurointermediate lobe as measured by bioassay. Much lower levels of immunoreactive alpha-MSH were found in the anterior lobe of the rat. Extracts of rat serum and plasma also contained immunoreactive alpha-MSH and the mean level was found to be 237 +/- 20 pg/ml. This was slightly lower than the level measured in rat plasma by bioassay. Increased levels of alpha-MSH were found in plasma of rats 1 and 3 h after a single injection of trifluoperazine and after 1-5 min of ether anaesthesia. These changes were reflected by decreases in the alpha-MSH content of the neurointermediate lobe.