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The monoamine oxidase (MAO) activity in the ovariectomized rat uterus was significantly increased above control levels in animals given testosterone: 33% (P smaller than 0.01) with tryptamine or 34% (P smaller than 0.05) with tyramine as substrate. Activity was also higher in hydrocortisone-treated animals: 30% (P smaller than 0.05) with tyramine or 25% (P smaller than 0.05) with tryptamine as substrate. Progesterone injection increased MAO activity toward tyramine by 20% but towards tryptamine by only 8%. The differences are not statistically significant but are believed to be real since they were reproducible. MAO activity in oestradiol-treated animals was 11% less than in the controls for both substrates. Although they are not significant differences, they were reproducible. No change in MAO activity was observed in the cerebellum, hypothalamus or anterior pituitary of ovariectomized rats after steroid treatment. At oestrus the enzyme activity in the uterus was lower than at dioestrus or prooestrus when beta-phenylethylamine was the substrate. When 5-hydroxytryptamine was used to measure enzyme activity, the same values were found at oestrus, dioestrus and prooestrus. Ovariectomy did not cause any changes in MAO activity in any of the tissues. Effects of the steroids in vivo were probably not due to a direct action on the enzyme since only at high concentration did they have any effect on the mitochondrial enzyme activity of the uterus in vivo.

Two isozymes of carbonic anhydrase (EC 4.2.1.1.) were compared in the anterior pituitary gland of non-tumor-bearing rats and in the hormone-secreting pituitary tumors. In contrast to the pituitary gland, which contained 60 to 70% of the total carbonic anhydrase in the particulate subcellular fraction, three hormone-secreting pituitary tumors were devoid of the particulate (Triton X-100-solubilized)enzyme activity. Another pituitary tumor, 7315a, contained particulate carbonic anhydrase, but the activity was only 45% of the activity of normal pituitary gland. During the development of the rat brain, the particulate (Triton X-100-solubilized) carbonic anhydrase activity was undetectable in prepartions up to 21 days of age (body weight, 47 g). After that age, the carbonic anhydrase activity in the particulate fraction increased rapidly and reached the adult level at 37 days (body weight, 120 g), while the activity in the soluble fraction increased gradually after birth and then reached a plateau at 30 days (body weight, 81 g). These data show that the isozyme pattern of carbonic anhydrase in pituitary tumor tissue resembles the pattern in fetal cells more than the pattern in adult tissue.

Two molecular forms of carbonic anhydrase were identified in the rat anterior pituitary gland. Electrophoretic and immunological studies disclosed that the low activity carbonic anhydrase (type B) was associated with the particulate fraction of the pituitary gland and the high activity carbonic anhydrase (type C) was localized in the soluble fraction. The 800 times g pellet contained 50% of the total activity of a pituitary homogenate prepared in 0.25 M sucrose, while the 105,000 times g supernatant accounted for an additional 30% of the total. The particulate enzyme was rendered soluble by treatment with Trition X-100. The activity of pituitary gland carbonic anhydrase was about 6 times greater in preparations from female rats as compared with males. The activity of carbonic anhydrase in the particulate fraction decreased, and the activity in the soluble fraction increased without a change in total activity following incubation in vitro of pituitary glands. The intracellular adjustment in enzyme activity was accompanied by the secretion of prolactin into the incubation medium by the pituitary gland. The secretion of prolactin and the solubilization of the particulate carbonic anhydrase was inhibited when the pituitary gland was incubated in the presence of 10-5 M dopamine.

Pituitary 5 alpha-reductase activity in intact male rats increases after the pituitary is incubated with the hypothalamus. Incubating the pituitary of castrate rats with the hypothalamus of intact rats relatively inhibits pituitary 5alpha-reductase activity. Coincubation of the pituitary and hypothalamus of castrate rats, or the pituitary of intact with the hypothalamus of castrate males, does not elicit changes in pituitary 5alpha-reductase activity. Different amounts of LH-RH in the incubation medium can modify 5alpha-reductase activity, i.e., activate it in the intact pituitary and inhibit it in the castrate pituitary. Hypothalamus from intact rats, which according to SHIN et al. [1974] is 'rich' in LH-RH, induces changes in pituitary 5alpha-reductase activity. The LH-RH-'poor' hypothalamus of castrate rats does not cause changes in this enzyme activity. The results suggest that there is a very close relationship between LH-RH and 5alpha-reductase activity in the pituitary.

The properties and subcellular distribution of anterior pituitary delta4-steroid (progesterone) 5alpha-reductase, which stimulates the conversion of progesterone to 5alpha-pregnane-3,20-dione, have been investigated utilizing 3H-substrate and a reverse isotopic dilution assay system. The enzymic activity was stimulated by NADPH but not NADH and exhibited a Km of 2.7+/-0.9 times 10(-7) M for progesterone. The substrate specificity of the enzyme for other delta4-3-ketosteroids and the effect of estradiol-17beta were also studied. 20alpha-hydroxy-4-pregnen-3-one was more reactive than progesterone, while testosterone was less reactive. Estradiol-17beta in vitro had an inhibitory effect on the 5alpha-reduction of progesterone. Studies on the subcellular distribution of the 5alpha-reductase activity indicate that the bulk of the activity was widely distributed amongst particulates sedimenting at 1,000, 15,000 and 100,000xg; with the 15,000xg pellet containing the most enzymic activity. The 100,000xg supernatant possessed only a small fraction of the total activity. After further fractionation of the 1,000xg pellet, the activity was distributed equally between the purified nuclear and cell debris-membranes fractions.

Ovine anterior pituitary glands contain mannosyl- and fucosyl-transferases localized in the microsomes and able to incorporate mannose or fucose as such from GDP-mannose or GDP-fucose into endogenous glycoproteins. The requirements and conditions necessary for maximum activity were investigated. The value of the Km is very similar for the two enzyme systems, 3 X 10(-7) M in the case of mannosyl-transferases and 5 X 10(-7) M in the case of fucosyl-transferases.

Subcutaneous injection of oestradiol-17beta enhanced the thymidine kinase activity in the anterior pituitary of immature male rats, but did not alter the thymidylate synthetase level. The kinase activity reached a sharp maximum 36 hours after injection of the steroid and then decreased to its original value. The estimated minimum active dose was 0.020 mug per rat. The 17alpha isomer was inactive. Cycloheximide and actinomycin D, according to injection schedule, prevented the rise in activity, suggesting a regulation of pituitary thymidine kinase at the level of protein biosynthesis. The induced enzyme exhibited the same Km and the same thermal inactivation profile as the constitutive enzyme. With the doses of oestradiol required for induction of the enzyme, no significant variations of serum and pituitary LH and FSH concentrations were detected. Based on these and previous results it is suggested that, in the male pituitary, the concentration ratio of circulating oestrogens over androgens controls not only the secretory function but also the production of specific enzymes.

The adenylate cyclase system in isolated plasma membranes of rat adenohypophyses was studied. Formation of cAMP was found to be dependent on plasma membrane protein. Production of cAMP could be stimulated by the addition of LH-RH. This process was shown to be a function of LH-RH concentration. Basal and stimulated cAMP could be stimulated by NaF. The results of the present experiments suggest that cAMP formation is time dependent. The synthesis of cAMP is a possible effector of LH-RH actions.