Abstract
Effects of short-term repeated blood sampling on the secretion of corticosterone (CORT) and β-endorphin (β-END) were evaluated in male Wistar rats. Blood was drawn from the tail vein of conscious rats four times within 2 h both at the peak and trough period of the diurnal corticosterone secretion cycle. All rats were well accustomed to the procedure. The main findings were: (1) At both sampling intervals, CORT increased significantly in response to the first sampling and declined to baseline values in successive samples. (2) β-END also increased significantly in response to the first sampling but remained elevated in successive samples. (3) Intensities of initial CORT and β-END responses correlated positively with each other and with the baseline β-END values. Feedback inhibition of CORT secretion with sustained elevation of β-END titres suggests a moderate stress intensity of the repeated blood sampling procedures. In general, due to lack of short-term feedback inhibition, β-END seems to reflect the effects of repeated administration of moderate intense stressors more closely than CORT.