Experimental modifications and changes with age in pineal succinic dehydrogenase activity

¹ Department of Zoology, University of California, Berkeley, California

Pineal succinic dehydrogenase was determined by means of reduction of 2,3,5-triphenyl-2H-tetrazolium chloride and colorimetry. Studies employing over 3300 rats, primarily of the Long-Evans strain, demonstrate that: a) Al⁺⁺⁺ and Ca⁺⁺ promote and Cu⁺⁺, malonate, iodine and hydroquinone inhibit enzyme activity in vitro; b) enzyme activity more than doubles in both sexes during the first 6 weeks postnatally with some reduction probable in about 1 year; c) pineal activity equals 50% of that of liver, 75% of tela chorioidea IV, 90% of cerebral cortex (area 18) and 160% of hypophyseal posterior lobe; d) norepinephrine or DOPA injection is usually followed (1–8 hours) by increased pineal activity; e) Dibenamine alone may depress activity after 18–19 hours but when followed by norepinephrine, DOPA, epinephrine, ephedrine, amphetamine or serotonin (4–6 hr. before autopsy) potentiates increased activity; f) Marsilid alone may stimulate activity (18 1/2–20 hr.) but when followed by norepinephrine, or DOPA potentiates decreased activity; g) extensive negative results with modifications in thyroid, adrenal cortical and gonadal endocrines do not support beliefs in pineal regulation by these pituitary-dependent systems. The hypothesis is advanced that the mammalian pineal is functionally involved with central mechanisms concerned with the metabolism and/or actions of certain neurohumoral amines.