A d r e n o c o r tic o tr o p ic H o r m o n e in R e la tio n to In te rre n a l F u n c tio n d u r in g S t r e s s in T ila p ia ( O r e o c h r o m is m o s s a m b i c u s )

diacetyl-tt-MSH. Evidence is presented that the noteworthy corticotropic potency of this HPLC fraction, previously attributed to diacetyl-tt-MSH, results from END and MSH acting in a coordinated fashion. Confinement stress had no effect on plasma N-ac-/?-END immunoreactivity, but led to a decrease in plasma or-MSH levels. Therefore, it seems unlikely that the corticotropic action of the peptides regulates the elevation of cortisol production that takes place during confinement, but it may play a role during other forms of stress that are known to activate the melanotropes.