Pineal influence on the diurnal rhythm of nonspecific immunity indices in chickens.

The effect of pinealectomy and melatonin injections on the diurnal rhythms of serum lysozyme and blood granulocytes was examined in White Leghorn cockerels kept from time of hatching for 5 weeks in L:D 12:12 conditions and immunized twice with sheep red blood cells (SRBC). Pinealectomy or sham-operation was made during first week of life. Pinealectomized chickens were injected daily with a melatonin dosage increased over 4 consecutive weeks (the dosage was 10, 13, 16, and 20 ng per bird daily during the 4 weeks, respectively; MEL I) at the beginning of darkness. The same treatment was performed on chickens with an intact pineal gland using additional melatonin doses increased 10 times (MEL II) and 500 times (MEL III). Intact chickens were also injected with MEL II and MEL III 4 hr before the end of light. Control birds received equivalent injections of vehicle. Five-week-old chickens were sacrificed during a 24-hr period every 4 hr. The existence of diurnal rhythm was evaluated by cosinor analysis. Pinealectomy shifted the acrophase of the diurnal rhythm of granulocytes and abolished that of serum lysozyme. Both rhythms were restored in pinealectomized chickens by MEL I but not by vehicle injections. The same melatonin dose was unable to change the granulocyte rhythm but delayed the acrophase of that of serum lysozyme in chickens with an intact pineal gland. Two higher melatonin doses influenced the diurnal rhythm of granulocytes as a function of dose and time of administration. The rhythm of serum lysozyme was dependent only on the time of injection. The pineal gland seems to control, via its hormone melatonin, the diurnal rhythm of nonspecific immunity in chickens.

Effect of dose and time of melatonin injections on the diurnal rhythm of immunity in chicken.

The effect of daily melatonin injections on the diurnal rhythm of immune parameters was examined in White Leghorn cockerels, kept from hatching in L:D 12:12 conditions. Subcutaneous injections of melatonin were made at the beginning of darkness or 4 h earlier for four weeks starting from one week of life. The melatonin dosage in one group was raised (10, 13, 16, and 20 ng per bird daily, respectively) during four consecutive weeks. The two other doses were 10 and 500 times higher and were increased every week as well. Control birds received equivalent injections of vehicle. Three-week-old chickens were immunized ip with sheep red blood cells and reimmunized one week later. Five-week-old birds were sacrificed during a 24 h period every 4 h. The existence of the diurnal rhythm was evaluated by cosinor analysis. The diurnal rhythm of total white blood cells and serum agglutinins was more dependent on the time of melatonin injections than on the hormone used. The effect of melatonin injections on the level of immune parameters examined was also dependent on the time of sample collection. Results obtained indicate the participation of pineal gland in the regulation of the diurnal rhythm of the examined indices of avian immune system function that exhibit diurnal changes in sensitivity to exogenous melatonin.