title: Control of Rat Testicular Monoamine Oxidase Activity: Age, Seasonality, Melatonin, HCG, FSH, Starvation and Irradiation
Creators: name: Urry, Ronald Lee
Publisher: name: Utah State University
Year: 1973

description: A number of investigations were undertaken to determine what factors control testicular MAO activity. Activity was high in neonatal rats (19 g - body weight), showed a reduced activity at 53 g, was increased at 145-235 g and showed a progressively reduced activity at 415 g, 482 g and 650 g. Hypophysectomy of immature male rats at 3 weeks of age, or mature rats at 10 weeks of age, significantly reduced testicular weight and total MAO activity as calculated on a per animal basis. The specific activity of the enzyme, as expressed on a per mg of tissue basis, was increased by hypophysectomy. Treatment of hypophysectomized rats with FSH increased testicular weight and total MAO activity. Additions of 2 IU or 5 IU of FSH to seminiferous tubules in tissue culture also increased testicular MAO activity. Treatment of hypophysectomized rats with a combination of FSH, LH and prolactin or treatment with hCG increased testicular weights but decreased MAO activity. This suggests that androgens may decrease MAO in vivo.
Injections of 1 or 2 mg of melatonin into mature hypophysectomized rats increased testicular MAO activity. Additions of melatonin in vitro at concentrations of 10-5 through 10-7 M also increased MAO activity. Treatment of male rats with either 10 or 100 μg of estradiol benzoate had no effect on testicular MAO activity. The activity was also not altered by adrenalectomy indicating that glucocorticosteroids may not play a role in regulating testicular MAO.
Restriction of feed intake by 47% reduced testicular MAO activity and this was attributed to a decrease in FSH. Restriction of feed by 67% increased pineal weight, hydroxyindole-O-methyltransferase activity, N-Acetyltransferase activity and testicular MAO activity; this increase was attributed to an increase in melatonin. Treatment of animals with 250 R whole-body x-irradiation increased MAO activity from 7-16 days after treatment. The increase in MAO activity 1 week after treatment corresponded with a previously noted increase in melatonin synthesis for the same period. Treatment of animals with 450 R of whole-body or testes only x-irradiation significantly decreased testicular weights and increased testicular MAO activity as expressed on a per mg of tissue basis. Irradiation with 450 R to the head-only lowered testicular MAO activity one-hour after treatment.
Pinealectomy increased testicular MAO activity, probably due to an increase in FSH levels. Testicular MAO did not appear to have a circadian rhythm in its activity.
Injections of pargyline, an MAO inhibitor, significantly inhibited testicular MAO while increasing endogenous serotonin concentrations.
Testicular MAO activity in the English house sparrow was observed to increase from November to April and to decrease from April through November. An increase in MAO activity from November to January preceded an increase in testicular weight. MAO activity and testicular weights of Uinta ground squirrels decreased dramatically from April to May as the animals went out of the breeding season.
Testicular MAO was observed to be localized mainly in the walls of the seminiferous tubules where it fluctuated with age. The ratio of activity in the seminiferous tubules to whole tissue was high in the young animal and low in older animals. Activity appeared to be lost in the seminiferous tubules during senescence faster than it was in the interstitial cells, thus shifting the ratio.
Treatment of animals with pargyline prevented return of testicular MAO activity in seminiferous tubules grown in tissue culture. Control seminiferous tubule MAO activity increased from 6 to 9 days after placing in tissue culture while those treated with pargyline did not have this increase.