Diurnal variation in the release of alpha-MSH from rat hypothalamus and pituitary.
Release of alpha-MSH from rat hypothalamic slices was characterized with respect to ionic requirements and possible diurnal variations using a sensitive radioimmunoassay. Addition of 47 mM KCl to the superfusion medium resulted in a twofold increase in alpha-MSH functions as a neurotransmitter or neuromodulator in the hypothalamus. Both spontaneous and potassium-induced alpha-MSH release compared to spontaneous release. Removal of calcium from the superfusion medium abolished the potassium-evoked release of alpha-MSH. This supports the concept that alpha-MSH release were related to diurnal variation. Marked release from the slices was observed at 10.10 h, corresponding to a peak in the alpha-MSH concentration in the hypothalamus [18] and to a lower levels of alpha-MSH in the blood. Contrarily, no significant release from the hypothalamus was obtained at 17.00 h when hypothalamic alpha-MSH content was low, but blood levels exhibited a peak. These findings suggest that there are differences in the regulation of the alpha-MSH from the pituitary and that in the hypothalamus.
D000818:Animals; D002940:Circadian Rhythm; D007031:Hypothalamus / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D010902:Pituitary Gland / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D009074:Melanocyte-Stimulating Hormones; D011188:Potassium