Season and physiological parameters modulate salmonid leucocyte androgen receptor affinity and abundance

Immune responses of ectothermic animals are known to vary seasonally. A loss of sensitivity to cortisol and testosterone (both normally immunosuppressive) in leucocytes from juvenile salmonids during winter has been previously documented. In an attempt to understand how the salmonid immune system changes in the winter, the present study investigated changes in androgen receptor affinity and abundance in salmonid leucocytes brought on by season, and physiological states such as stress and sexual maturation. In sexually immature fish, leucocyte androgen receptor affinity dropped more than four-fold during winter. TheKdrose from less than 1 nMin July to 4 nMin January. The number of androgen receptors present also rose dramatically in January (from 50 fmol mg−1protein to 400 fmol mg−1protein). An 18 h confinement stress caused a significant drop in leucocyte androgen receptor binding affinity in sexually immature fish (Kdrose to 6 nMfrom 2·7 nM) but had no effect on the number of receptors present. Sexual maturation of rainbow trout led to an increased number of leucocyte androgen receptors, similar to the number seen in immature fish sampled during the spawning season (300 fmol mg−1protein), and leucocyte androgen receptor affinity decreased significantly after ovulation (Kd14 nM, up from 4 nMbefore ovulation).