Diurnal Variation in the Release of Alpha-MSH from Rat Hypothalamus and Pituitary

Abstract

Release of α-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 α-MSH release compared to spontaneous release. Removal of calcium from the superfusion medium abolished the potassium-evoked release of α-MSH. This supports the concept that α-MSH functions as a neurotransmitter or neuromodulator in the hypothalamus. Both spontaneous and potassium-induced α-MSH release were related to diurnal variation. Marked release from the slices was observed at 10.10 h, corresponding to a peak in the α-MSH concentration in the hypothalamus [18] and to a low level of α-MSH in the blood. Contrarily, no significant release from the hypothalamus was obtained at 17.00 h when hypothalamic α-MSH content was low, but blood levels exhibited a peak. These findings suggest that there are differences in the regulation of the α-MSH from the pituitary and that in the hypothalamus.

Changes in Alpha-Melanocyte-Stimulating Hormone Content in Discrete Hypothalamic Areas of the Male Rat during a Twenty-Four-Hour Period

“…This could indicate that the values of releasable a-MSH in the hypothalamus is not necessar ily identical with its a-MSH content. How ever, our own results on circadian changes in hypothalamic content of a-MSH parallel the findings of Monnet et al [25] on circadian a-MSH release and support the view that hypothalamic and pituitary regulation of a-MSH biosynthesis differ from each other.…”

“…A diurnal variation of a-MSH in rat plasma and in its release from hypothalamic slices has been reported by Monnet et al [25] who showed peak values in plasma at 03.00 h and -to a lesser extent -at 18.00 h. The release from hypothalamic slices was marked at 10.00 h but only marginal at 17.00 h. These authors suggested a differ ence in the regulation of a-MSH release be tween the pituitary and the hypothalamus. In contrast, O'Donohue et al [26] found a peak of a-MSH content in the hypothalamus during the light period; they related the diur nal variations with circadian changes in pi tuitary and blood a-MSH content.…”

Melanocortin-5 Receptor Deficiency in Mice Blocks a Novel Pathway Influencing Pheromone-Induced Aggression

“…In the present study, NDP-MSH was administered and behavioral testing occurred in the middle of the light phase. This was done to minimize aggression that might be due to elevated melanocortin secretion in the dark phase (Monnet et al, 1981;Millington et al, 1986).…”

Lack of effect of a behaviorally active dose of?-melanotropin on biochemical indices of dopaminergic neuronal activity in the rat

“…a-MSH has been identified in perikarya in the arcuate nucleus (Eskay et al, 1979;O'Donobue et al, 1979) and the perifomical region of the hypothalamus Aleil, 1979, 1980). It has also been reported that a-MSH is released by potassium in a calcium dependent manner from hypothalamic slices in vitro (Monnet et al, 1981;O'Donohue et al, 1981), and concentrations of a-MSH in the cerebrospinal fluid are increased by electrical stimulation of the mesencephalic central gray in vivo (O'Donobue et al, 1981).…”