Day Time and Night Time Magnitude of Adrenal Response to Immobilization Adrenocorticotropin in Rams

D. GUDEV, S. ALEXANDROV, S. POPOVA-RALTCHEVA and A. ALEXANDROV

Research Institute of Animal Science, BG-2232 Kostinbrod, Bulgaria

Abstract

GUDEV, D., S. ALEXANDROV, S. POPOVA-RALTCHEVA and A. ALEXANDROV, 2000. Day time and night time magnitude of adrenal response to immobilization adrenocorticotropin in rams. Bulg. J. Agric. Sci., 6: 227-231

Day time melatonin concentration in sheep is under sensitivity of RIA method and night time melatonin concentration is within 500-800 Fmol/ml. Thus the purpose of our study was to determine adrenal and gonadal response to stress during the day and during the night in December and June.
Six rams were subjected to stress by the injection of exogenous adrenocorticotropin or by immobilization for 60 min.
Night time samples were taken at 1900 h and 2300 h in winter and summer, respectively.
Plasma cortisol was used as indicator of adrenal function and plasma testosterone – as indicator of testes function.
It was established that photoperiod doesn't influence adrenal response to immobilization or adrenocorticotropin injection both in summer and winter. Furthermore day time and night time melatonin doesn't influence the inhibitory effect of exogenous adrenocorticotropin on testosterone secretion.
Adrenal response to immobilization was weaker compared to adrenocorticotropin injection both in summer and winter.

Key words: melatonin, adrenal function, gonadal function, stress
Abbreviation: RIA – radioimmuno assay, HPAA – hipothalamopituitary adrenal axis, HPGA – hipothalamopituitary, HSD – hydroxysteroid dehydrogenase