Demonstration of an endogenous circadian rhythm of alpha-melanocyte stimulating hormone in the rat pineal gland.
alpha-Melanocyte stimulating hormone (alpha-MSH) has been identified and characterized in the rat pineal gland by a combination of immunochemical and high pressure liquid chromatographic techniques. The immunoreactivity in pineal extracts was separated into two chromatographic components. The major component had a retention time identical to that of alpha-MSH while the minor component eluted just slightly before standard alpha-MSH. Male rats maintained in a 12 h photoperiod demonstrated a marked circadian rhythm in pineal alpha-MSH concentration. Concentrations that peaked at 07.00 h, 1 h after the lights were turned on, were greater than 5 times the nadir which occurred at 01.000 h. Animals house in chronic dark for 7 days maintained the diurnal variation of alpha-MSH concentrations. However, in chronically dark housed rats, the peak shifted to 05.000 h and was greater than 10 times the nidir of this rhythm and approximately 4 time the peak at 07.00 in alternating light/dark conditions. Rats exposed to chronic light for 7 days maintained a pineal alpha-MSH rhythm although the amplitude of the peak was significantly decreased compared to the rhythm in animals housed in alternating light/dark conditions. Neither hypophysectomy nor superior cervical ganglionectomy had any effect on the alpha-MSH rhythm. Lesion of the arcuate nucleus, the major source of alpha-MSH-containing nerves in the brain, did not significantly affect pineal alpha-MSH concentrations. These data demonstrate a circadian alpha-MSH rhythm in the rat pineal and suggest an alpha-MSH involvement in the rhythmic processes of the pineal gland.
D000818:Animals; D002853:Chromatography, Liquid; D002940:Circadian Rhythm; D005728:Ganglia, Sympathetic / Q000502:physiology; D007033:Hypothalamus, Middle / Q000502:physiology; D008027:Light; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D010870:Pineal Gland / Q000378:metabolism*; D010902:Pituitary Gland / Q000502:physiology; D011863:Radioimmunoassay; D051381:Rats
D009074:Melanocyte-Stimulating Hormones