Diurnal variations in circulating estradiol, testosterone, melatonin and harderian gland porphyrin concentration in Indian palm squirrel, Funambulus pennanti.

A two-peak cyclicity in the plasma level of melatonin, estradiol/testosterone and Harderian porphyrin was noted in F. pennanti. An inverse relationship of Harderian porphyrin with plasma melatonin and a direct relation of it with plasma estradiol/testoserone level were also observed, suggesting that the variation of Harderian, porphyrin concentration may be under the control of both, circulating melatonin and gonadal steroids.