INTRAVITREAL APPLICATION OF MEMBRANE-PERMEABLE ANALOGS OF CYCLIC-GMP INCREASES SEROTONIN N-ACETYLTRANSFERASE (NAT) ACTIVITY IN RETINAS OF LIGHT-EXPOSED CHICKS - COMPARISON WITH THE EFFECT OF CYCLIC-AMP ANALOGSAND DARKNESS

Intravitreal administration of membrane-permeable analogs of cGMP and cAMP markedly enhanced serotonin N-acetyltransferase (NAT) activity in retinas of light-exposed chicks. The effects of cGMP analogs were usu ally weaker than the actions of cAMP analogs, however, they were more pronounced than the effects of non-cyclic derivative of GMP (i.e., 8-b romo-GMP). Combined treatment with dibutyryl-derivatives of cGMP and c AMP yielded NAT values that were similar to the values produced by the compounds administered separately, whereas NAT activity in chicks rec eiving a combination of db-cGMP and aminophylline was higher than the enzyme activity produced by the drugs individually. Neither db-cGMP no r aminophylline affected hydroxyindole-O-methyltransferase (HIOMT) act ivity in retinas of light-exposed chicks. It is hypothesized that cGMP analogs enhance the retinal NAT activity indirectly, via cAMP.