Monoamine Oxidase as a Target Enzyme in Pineal and Testicular Tissue: Adrenal Cortical Steroids and Arginine Vasotocin

The purpose of the research was twofold: (a) To ascertain what effects the adrenal glucocorticoids and catecholamines have on pineal N-acetyltransferase and monoamine oxidase activity, and (b) to observe what effect arginine vasotocin (a pineal polypeptide) has on testicular monoamine oxidase activity. Rat pineal N-acetyltransferase activity was numerically increased when rats were injected with cortisol. It was increased significantly when the animals were injected with cortisol plus norepinephrine. Adrenal demedullation significantly increased N-acetyltransferase activity in starved rats when compared with intact control animals. Moreover, bovine pineal monoamine oxidase activity was markedly inhibited in a dose-dependent manner when incubated in vitro with cortisol. The results strongly implicate the adrenal gland as one factor controlling melatonin synthesis by the pineal gland, especially with food deprivation. Arginine vasotocin, a polypeptide consisting of eight amino acids, was incubated with rat, hamster and rabbit testicular monoamine oxidase. The polypeptide significantly inhibited rat and hamster enzyme preparations, but had no effect on the rabbit population. These data suggest that the pineal may act peripherally to decrease reproductive function partially through a serotonergic mechanism involving the enzyme monoamine oxidase