Seasonal relationships between plasma and fecal testosterone in response to GnRH in domestic ganders

In two groups (eight individuals each) of socially acquainted, outdoor-kept , domestic ganders (male Hungarian white: Anser domesticus), basal and GnRH -stimulated plasma testosterone (T) concentrations were compared with fecal testosterone metabolites (TM) in and between three seasons, spring peak of reproductive activity, summer photorefractoriness, and fall sexual reactiv ation. Plasma was sampled 90 min following the challenge and T was analyzed by radioimmunoassay following the GnRH challenge. Fecal TM were measured b y enzyme immunoassay using two group-specific antibodies against 17 beta-OH -androgens or a novel antibody against 17-oxo groups, which was found to re act with major testosterone metabolites without prior hydrolytic deconjugat ion. Baseline plasma T and systemic levels were high in spring and fall but low in summer. Plasma T increases in response to GnRH were followed by sig nificantly elevated fecal TM levels 2 to 6 h following the challenge in spr ing and fall. In fall, at high plasma T levels, fecal TM levels were dispro portionally lower than in spring. Variability of TM levels was two to five times higher in feces than in plasma, which explains why correlations betwe en individual plasma T and fecal TM levels generally remained nonsignifican t. This points to a low-level shortterm relationship between the excreted T M and the plasma T levels. However, the reliability of the method was demon strated by standard inter- and intraassay variablilities and by a high corr espondence between results obtained by the two assays. It is suggested that , with appropriate sample size, fecal TM reflects plasma T increase. Howeve r, fecal TM was more variable than the plasma T, and fecal TM responses to GnRH did not always parallel the plasma T response. In addition, seasonal c hanges in androgen excretion regimes must be taken into account. (C) 2000 A cademic Press.