CORTICOTROPIN-RELEASING HORMONE STIMULATES ADENYLYL-CYCLASE ACTIVITY IN THE RETINAS OF DIFFERENT ANIMAL SPECIES

In the present study we investigated the presence of corticotropin-rel easing hormone (CRH)-stimulated adenylyl cyclase activity in the retin as of different animal species. CRH significantly stimulated adenylyl cyclase activity in homogenates of calf, pig, rabbit and guinea pig re tinas. The stimulatory effects were concentration-dependent with half- maximal responses occurring at 20-30 nM CRH. The enzyme activities inc reased by 37-80% at the maximal concentration of CRH (1 muM). On the o ther hand, adenylyl cyclase activities of chicken and pigeon retinas w ere poorly stimulated by CRH. In calf, pig and rabbit retinas, the CRH effect was completely antagonized by the CRH receptor antagonist alph a-helical CRH 9-41 and required the presence of GTP. The stimulatory r esponse elicited by CRH was also found to be not additive with that pr oduced by either vasoactive intestinal peptide or dopamine. These resu lts provide evidence for the presence in retinas of different animal s pecies of functional CRH receptors, an important criterion for the cla ssification of CRH as a retinal neurotransmitter.