Diurnal sensitivity in melatonin-induced hematological changes in the male albino rat.

The influence of melatonin on diurnal changes in the hematological profile was investigated in male albino rats. Following treatment with melatonin, under two different experimental protocols, blood samples were collected at 06.00, 12.00, 18.00 and 24.00 h from separate groups of animals for detailed hematological analysis. In experiment 1, melatonin (25 micrograms, s.c.) treatment, once daily at 17.00 h for 4 weeks, led to an alteration in the rhythm of RBC production with a decrease in its counts at 12.00 h. The total WBC counts were increased at 06.00 and 12.00 h and decreased at 18.00 and 24.00 h. In experiment 2, twice-daily administration of melatonin (once at 09.00 h and again at 17.00 h), for 2 weeks, resulted in a decrease in total RBC counts at 06.00 and 24.00 h, whereas at 18.00 h there was an increase, compared to the respective control values. The total WBC counts increased at 06.00, 12.00 and 18.00 h and decreased at 24.00 h. Erythrocyte indices like mean cell volume (MCV), mean cell hemoglobin (MCH) and mean cell hemoglobin concentration (MCHC), in both experiments, correlated with RBC, hemoglobin and hematocrit values. The WBC differential counts in experiment 1 revealed a decrease in total neutrophils at 24.00 h, whereas in experiment 2 there was a general decrease in their number. While in experiment 1 the total lymphocyte number was increased at 06.00 h and decreased at 18.00 and 24.00 h, in experiment 2 it was increased except at 24.00 h. It may be concluded that melatonin has a modulatory role in hemopoiesis and its rhythms. The stimulatory effect of melatonin on WBC supports its purported immunopotentiating action.

Influence of melatonin on blood morphology in male albino mice.

Influence of melatonin on diurnal changes in hematological profiles was examined in male albino mice, at six hourly interval. Melatonin treatment either once daily (25 micrograms at 1700 hrs) or twice daily (25 micrograms at 0900 and 1700 hrs) for two weeks resulted in an alternation in the RBC rhythm. Generally the effect was suppressive though at some times the counts were marginally increased. Total WBC counts were increased and there was apparently a change in their rhythm too. Interestingly the differential WBC counts exhibited different patterns in, once and twice daily melatonin-treated mice. Melatonin given once daily predominantly stimulated the absolute lymphocyte count whereas the twice daily regimen predominantly stimulated the neutrophil count. This perhaps is related to the varied exposures of the animals to melatonin in the two experimental setups. Erythrocyte indices like mean cell volume, mean cell hemolglobin and mean cell hemoglobin concentration in both the experiments correlated with hemoglobin and hematocrit values. It may be concluded that melatonin has a modulatory role in hemopoiesis and its rhythms. The stimulatory effect of melatonin on WBC supports its purported immunopotentiating action.