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Melatonin functions in the control of melanophore pigmentation of amphibians but its role in higher vertebrates is ill-defined. In mammals melatonin is produced within the pineal gland, where its formation is light dependent. This study consisted of three experiments: (i) a biological assay of commercial preparations of melatonin; (ii) response of hibernating ground squirrels exposed to cold and melatonin; (iii) response of isolated hearts to melatonin. Commercial preparations of melatonin were compared for their biological effectiveness by measuring the inhibition of compensatory ovarian hypertrophy in laboratory mice. Unilateral ovariectomy results in hypertrophy of the intact ovary of untreated mice. Unilaterally ovariectomized mice were given an intraperitoneal injection of physiological saline (controls) or 100 µg of melatonin immediately following ovariectomy. Measurement of compensatory ovarian hypertrophy was made 10 days following the ovariectomy. Although the four commercial preparations produced significant inhibition when compared to the controls, there was one preparation (Calbiochem) which was noted to be significantly less biologically effective in inhibiting ovarian hypertrophy than the other three commercial preparations. Daily subcutaneous injections of a biologically effective commercial preparation of melatonin increased the frequency and duration of hibernation of ground squirrels, Citellus lateralis. Control animals received injections of saline solution. In one series, each animal served as its own control. Dosages of malatonin were 100 or 500 µg per day. Observations for hibernation were made twice daily by means of a skin temperature measurement. Isolated hearts from ground squirrels (C. lateralis and C. spilosoma) and laboratory mice (M. musculus) were excised immediately following decapitation and placed within a Locke's mammalian Ringer's solution maintained at 5 C for the ground squirrel hearts and 20 C for the laboratory mice hearts. The isolated hearts were monitored for activity by measuring the duration of electrical activity between the right auricle and the right ventricle. The addition of melatonin, 1 µg/cc of Ringer's solution, depressed the duration of electrical activity of the isolated hearts by approximately 26% in the lab mice and 43% in the ground squirrels.



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Department Name

UNM Biology Department

First Committee Member (Chair)

Marvin LeRoy Riedesel

Second Committee Member

David Lee Vander Jagt

Third Committee Member

Paul Richard Kerkof

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