Seasonal variation in specific plasma- and target-tissue binding of XXXX , relative to plasma @entity134 levels, in the brown trout, Salmo trutta L.

@entity251 @entity5444 @entity5090 @entity134 @entity342 @entity3800
The circulating levels of the plasma @entity3800 , @entity251 and @entity5444 , and their specific binding to skin cytosol, skin nuclear extract, and plasma were determined in mature male and immature male and female brown trout during a single spawning cycle. @entity5444 was not bound by any of the fractions examined whereas @entity251 was bound with high affinity to plasma (kD = 32.6 nM), skin cytosol (kD = 16.9 nM), and skin nuclear extract (kD = 2.6 nM). The binding capacity of each fraction varied independently with time. In mature male fish an increase in specific binding of @entity251 to nuclear extract, from 77 to 269 fmol @entity5090 protein, occurred between September and November, coincident with peak @entity342 levels. Following the spawning period and the decline in @entity342 levels, nuclear-binding capacity in mature fish dropped to a level similar to that of immature fish by June. Nuclear binding in immature fish remained in the range 25-75 fmol @entity5090 protein throughout. Plasma-binding capacity of both mature and immature fish declined during the spawning period, from 190 to 125 nM in mature fish and from 360 to 125 nM in immature fish. Plasma-binding capacity in both mature and immature fish increased following spawning to reach levels of 340 nM (mature) and 250 nM (immature). Little change was observed in cytosol-binding capacity of either mature or immature fish. The results suggest that @entity342 -induced structural changes in the integument are predominantly @entity251 stimulated, are initiated by an increase in the concentration of a specific @entity251 -binding protein within the nucleus, may be potentiated by a drop in plasma @entity251 -binding capacity, and that a cytosol-binding protein of intermediate affinity for @entity251 may maintain a high intracellular concentration of @entity134 .
