Diurnal variations of urinary 6-sulphatoxymelatonin in male intact or ganglionectomized mink.

The existence of the major urinary metabolite of melatonin, 6-sulphatoxymelatonin (aMT6s), was validated for mink and the 24 hr urinary excretion pattern was determined in intact and superior cervical ganglionectomized animals under different photoperiodic conditions. Within- and between-assay variations, parallelism between serially mid-night pooled urine dilutions and standard curves in aMT6s free urine of mink at 1:125 dilution and recovery of aMT6s in mid-day pooled urine at 1:125 dilution provided a good validation for the mink urinary a MT6s assay. In natural photoperiods (January, LD 9:15; April, LD 13:11) the diurnal rhythm was characterized by low aMT6s values during the day and high values at night. There were no differences in the nocturnal values measured under long- (April, 4.11 +/- 0.40 ng/hr) or short-day (January, 4.74 +/- 0.36 ng/hr) conditions. In an experimental long photoperiod (LD 15:9), the same result was obtained on the 24 hr rhythm in intact animals, but in ganglionectomized mink the nocturnal rise in aMT6s was abolished and the nocturnal values were always low (0.88 +/- 0.09 ng/hr). Our results agree with those obtained in other species concerning plasma melatonin rhythm and urinary aMT6s excretion; we thus conclude that this is an effective assay for measuring pineal activity in mink.