Short-term responses of plasma norepinephrine, epinephrine, glucocorticoid and testosterone titers to social and non-social stressors in male guinea pigs of different social status.

The short-term effects on norepinephrine (NE), epinephrine (E), glucocorticoid (CS) and testosterone (T) levels of (a) taking blood samples, and (b) an agonistic encounter in an experienced fighter's home cage were examined in 15 male guinea pigs living in large heterosexual colonies for 8 to 19 months. Four tests were performed 1 month apart. In the 1st, 2nd and 3rd test 3 blood samples were taken from each male in a strange room within 30 min (sampling times were designated as 0, 20 and 30 min, respectively). In the 4th test blood samples were taken on the same time schedule, however, the males were given 10 min agonistic encounters 10 min after the initial blood sampling. The main findings were as follows: in response to taking blood samples and fighting CS and NE titers increased significantly, whereas E values did not change in a significant way. T titers decreased 10 min after the agonistic encounter. The % changes of NE, E, CS and T at 20 and 30 min did not differ whether an agonistic encounter took place or only blood samples were taken. According to their behaviors displayed in the colonies the males were divided into high (N = 6) and low (N = 9) ranking individuals. When only blood samples were taken the males' social status was only reflected by a tendency towards higher T levels in high ranking males, however not by NE, E and CS titers. High ranking males showed lower NE titers than low ranking males directly after the agonistic encounter. No further relationships between long-term social status and short-term endocrine responses were found. According to their behaviors displayed during the agonistic encounters the males were divided into fighters (F) (5 out of 6 high and 3 out of 9 low ranking individuals), and non-fighters (NF) (1 high, 6 low ranking individuals). F and NF did not differ in T and CS values, NE titers, however, were significantly higher in NF compared with F before, directly after the encounter as well as 10 min later. E was significantly higher in NF than in F directly after the encounter. One month before the contest prospective NF showed higher NE levels at 0, 20 and 30 min sampling times than prospective F when only blood samples were taken. These findings point to a more important role of catecholamines than CS and T in guinea pig intermale agonistic encounters. NE responsiveness may have predictive value for the behavior in contest situations.