Catecholam1ne metabolism and monoamine oxidase activity tn adrenalectomized rats

Abstract

The excretion of 4-hydroxy-3-methoxyphenylglycol (HMPG), 4-hydroxy-3-methoxymandelic acid (VMA), metadrenaline (MA), normetadrenaline (NMA) and homovanillic acid (HVA) has been measured in the urine of adrenalectomized rats. Urinary HMPG was significantly increased compared with the controls, presumably reflecting an increased production of noradrenaline. HVA output was similarly increased although to a lesser extent. Treatment with hydrocortisone (10 mg per kg) for 7 days abolished these increases. A small amount of urinary MA was still detectable in four out of six adrenaiectomized rats, providing further evidence for extra-adrenal production of adrenaline. VMA and NMA excretion were not significantly altered by adrenalectomy. After adrenalectomy, changes in the subcellular distribution of monoamine oxidase (MAO) are complex and vary from tissue to tissue. Total activity in heart, brain and vas deferens of adrenalectomized rats was significantly increased, a reflection of increased mitochondrial activity. An increase in microsomal MAO was observed only in the vas deferens. The heart was the only tissue examined to show an increase in the supernatant fraction. In the duodenum mitochondrial MAO activity was significantly increased, but this rise was offset by a significant decrease in enzyme in the supernatant fraction.