Measurement of vitellogenin from rainbow trout by rocket immunoelectrophoresis: application to the kinetic analysis of estrogen stimulation in the male

The study of the seasonal regulation of vitellogenesis in rainbow trout (Salmo gairdneri) is hampered by two features of the system which are not seen in species such as Xenopus. First, it is impossible to sex immature trout by external appearance and, secondly, the quantitation of the very low levels of vitellogenin in previtellogenic serum is technically difficult and tedious. We describe the preparation of a specific, sensitive anti-vitellogenin antibody and the use of this antibody in a rocket immunoelectrophoresis system to measure serum vitellogenin. The sensitivity of the assay is such that, using only 2 μL of serum, it is possible to detect vitellogenin at levels of 10 μg/mL, making this assay extremely useful for selecting immature female trout for further studies on the basis of the presence of vitellogenin. Using this system we have also measured the response of individual male trout to stimulation with different levels of estradiol, and we have shown that it is possible to measure the stimulation of vitellogenin by estradiol levels equivalent to those seen during the previtellogenic phase of the reproductive cycle in females. This simple assay system thus alleviates two of the major hurdles in studying vitellogenesis in trout.