A subcutaneous single injection of progesterone at certain early hours on the day of proestrus caused an advanced increase in ovarian progesterone secretion 2 to 3 hrs. before the time of its spontaneous preovulatory increase in 4-day cyclic rats. The secretion of 20α-hydroxypregn-4-en-3-one (20α-OH-P), however, was not significantly altered by exogenous progesterone. Such an effect of the exogenous progesterone on the preovulatory secretion of progesterone was not seen when rats were hypophysectomized or when treated with phenobarbital just before progesterone injection or they were at the stage of diestrus. The results indicate that the progesterone effect is mediated through neural factors controlling luteinizing hormone (LH) release from the pituitary. Our previous works have demonstrated that a preovulatory increase in progesterone secretion occurs on the evening of the day of proestrus and is entirely dependent upon the release of LH from the pituitary. Other endogenous steroids such as 20α-OH-P, estradiol, estriol, testosterone, and 5-androstenediol produced no such a promoting effect on the preovulatory progesterone secretion. It is suggested, therefore, that 20α-OH-P plays no physiological role in the regulation of LH release in the rat. The interdependency between LH release and progesterone secretion was discussed, and neither negative nor positive feed-back control mechanism was accepted for the preovulatory secretions of LH and progesterone in the cyclic rat.

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A single subcutaneous injection of progesterone (5mg/rat), chlormadinone acetate (CMA, 17α-acetoxy-6-chloro-pregna-4, 6-diene-3, 20-dione; 5mg/rat), medroxyprogesterone acetate (MAP, 17α-acetoxy-6α-methyl-pregn-4-ene-3, 20-dione; 0.5mg/rat) or norethindrone (17α-ethyny1-17β-hydroxyestr-4-en-3-one; 0.5mg/rat) into 4-day cyclic rats at 11 a. m. on the 2nd day of diestrus inhibited spontaneous ovulation on the day corresponding to the following estrus. Also, oral administration of CMA or MAP inhibited ovulation completely at the dosage of 5 mg per rat, whereas norethindrone given in the similar manner did not exhibit the same effect. No inhibition of ovulation was observed in the rats to which norethynodrel (17α-ethyny1-17β-hydroxyestr-5 (10)-en-3-one) had been given either by subcutaneous or by oral route at the dosages up to 10 mg per rat. Of the other steroids tested, androgen was the only one that inhibited spontaneous ovulation. Progesterone, MAP, CMA and norethindrone, administered atthe dosage of 10 mg per rat 50 hrs. after the initial progesterone treatment, restored ovulation in 24hrs., which had been expected to be delayed with 3 mg of progesterone given at 11 a. m. on the 2nd day of diestrus. These results indicate that synthetic progestins as well as progesterone have a biphasic action, inhibitory and facilitatory, on the neural mechanism (s) regulating the release of luteinizing hormone in the rat.

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Further studies were made on the causal relationship between estrogen secretion and LH release by investigating the effects of exogenous estrogen on the progesteroneinduced delay in ovulation in the 4-day cyclic rats under the constant lighting regimen from 8a. m. to 8p. m. It was previously demonstrated that progesterone (3mg/rat) administered during the period between the morning of the day before proestrus (diestrus II) and 2a. m. proestrus caused an approximately 48-hr. delay in ovulation and that estrogen secreted till 4-7a. m. proestrus was necessary for ovulatory discharge of LH, which occurred between 5 and 7p. m. proestrus under our lighting schedule. Estrogen administered between 3 and 5p. m. on diestrus II completely restored ovulation, which was otherwise expected to delay by 48 hr. with progesterone given at 11a. m. diestrus II. In the rats injected with progesterone at 2a. m. proestrus and again with estrogen at 6a. m. proestrus, ovulation occurred on the day expecting estrus, but did not occur in the rats receiving progesterone 8p. m. or earlier in diestrus II followed by estrogen at 6a. m. in proestrus. It is suggested, therefore, that the effect of integrated amount of estrogen from the afternoon of diestrus II until the morning of proestrus is responsible for the neural mechanism (s) to induce ovulatory discharge of LH in late proestrus.

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The isolated anterior pituitary of the rat produced a greater amount of ¹⁴CO₂ from glucose-1-¹⁴C than from glucose-6-¹⁴C. Thyroidectomy resulted in a significant increase in the 14CO2 production from glucose-1-¹⁴C by the anterior pituitary, and the increased ¹⁴CO₂ output was suppressed to the normal level 72 hr. after L-thyroxine (T₄) administration in vivo. Oxidation of glucose-U-₁₄C and glucose-6-¹⁴C was also increased slightly after thyroidectomy, but the C1/C6 ratio of ¹⁴CO₂ was greater in the thyroidectomized group than in the normal control. These data show that the hexose monophosphate pathway in the anterior pituitary is markedly stimulated after thyroidectomy and seem to indicate that ¹⁴C-glucose oxidation via glycolysis is also accelerated to a lesser extent. Incorporation of ¹⁴C-glucose carbon into glycogen, RNA and protein was accelerated after thyroidectomy and returned to the normal levels 72 hr. after T₄ supplement. The absolute amount of glucose consumed by the anterior pituitary increased after thyroidectomy and returned to normal 72 hr. after T₄ supplement. In contrast, the formation of radioactive lipids from ¹⁴C-glucose was reduced by thyroidectomy and returned to normal 72 hr. after T₄ supplement. The correlation of the glucose metabolism in the anterior pituitary with the protein and RNA synthesis was discussed, with special reference to the functional state of the thyroid gland.

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This report deals with a new technique developed by the author to isolate various types of anterior pituitary cells. Some of the principal procedures involved in this technique are: 1) initial digestion of pituitary tissues by trypsin in a calcium-and magnesium-free buffer solution of Rinaldini, 2) filtration of the dissociated cells through the stainless steel mesh, 3) treatment of the filtered cells with elastase and collagenase to prevent their aggregation and aggultination, 4) and final separation of the cells according to their types by centrifuging dextran A on the discontinuous gradient to which the filtered cells were added. Light and electron microscopic examinations of all the fractions after centrifugation confirmed a perfectseparation of chromophobes, undifferentiated cells of ambiguous nature, and intermediate cells between chromophobes and chromophils. However, the acidophils and basophils isolated by our technique were found intermingled with a small number of the intermediate cells.

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The pellets of chromophobes selectively isolated from the fresh rat pituitaries according to the procedure of Ishikawa (1969) were homotransplanted in the hypophysiotrophic area of hypophysectomized rats. Prior to transplantation, the pellets were examined histologically to confirm no contamination with cells of the other kind. In the early phase, up to 24hr. after transplantation, chromophobes proliferated through mitosis. In the middle phase, from 36hr. to 7days, they differentiated into acidophils or basophils to a degree via intermediate cells. Mitotic division which preceded differentiation led to further proliferation. In the later phase, from 10 to 30 days after transplantation, the chromophobes were completely transformed into two types of chromophils without undergoing mitosis. Thus, a direct evidence was adduced that the chromophobes were transformed into chromophils along the acidophil-and basophilaxes. From the findings on the pellets grafted beneath the renal capsule or into the cerebral cortex in controls, it was postulated that hypothalamus not only exerted a strong action on the chromophobes to make them differentiate into chromophils, but also reorganized the isolated chromophobes into the anterior pituitary.

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The authors previously noted a more significantly decreased response of lipoprotein lipase activity to dextran sulfate injection in diabetic patients than in normal subjects and suggested that the lowered plasma lipoprotein lipase activity may contribute to hypertriglyceridemia in diabetic patients. In the present report the authors have studied on human subjects and rats with and without diabetes, the regulation of lipoprotein hpase activity in postdextransulfate plasma and tissues following administration of glucose or fat. In normal subjects the response of plasma lipoprotein lipase activity to injected dextran sulfate one hr. after feeding or oral glucose administration was significantly higher than the response after an over night fast. In diabetic patients, however, the difference between feeding or glucose administration and over night fast was insignificant. In normal rats the increase of tissue lipoprotein lipase activity to intravenously administered glucose was significant in adipose tissue and insignificant in muscles. After intravenous fat administration no significant changes were observed either in aciinose tissue or in muscles. In alloxan diabetic rats decrease in activity of lipoprotein lipase was significant in adipose tissue, but insignificant in heart muscle and diaphragm compared with normal rats. From the facts above it is suggested that markedly elevated plasma lipoprotein lipase activity after glucose loading in normal subjects is released from tissue in response to intravenously administered dextran sulfate. The authors have also discussed the probability of induction of lipoprotein lipase in adipose tissue by the metabolic effects of glucose and/or insulin.

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Lactating mice were injected subcutaneously with 0.125, 0.25 and 1 I.U. of oxytocin twice daily from day 4 to day 8 of lactation. A graduated decrease in litter growth was observed with increasing amounts of oxytocin. The average litter gains were significantly lower in oxytocin treated groups than in saline injected controls during the injection period. On the other hand, the average increases and % increases in the body weight of the mother were greater in oxytocin injected groups than in controls. The nursing behavior of the mother was not influenced by the treatments but a marked accumulation of milk was observed in the mammary glands of the oxytocin injected mother, while young vigorously suckled the teats. After the withdrawal of oxytocin treatment, the growth rate of litter did not recover and several young died of starvation in a group received larger doses of oxytocin. The body weight of the mother, which had been increased by oxytocin, was reduced to the control level. Quite similar results were obtained in another experiment which was carried out duplicatedly. Oxytocin administered either subcutaneously or intravenously, 0.125, 0.25, 0.5 or 1 I. U. twice daily, significantly inhibited the litter growth with increasing doses irrespective of different brands of oxytocic preparation. There was no significant difference in the inhibitory effect on litter growth between routes of administration at the same dose level. An inhibitory effect on litter growth tended to be heightened in a regimen of 9.00a. m.-2.00p. m. administration of oxytocin than in a regimen of 9.00 a. m.-6.00 p.m. When killed on day 15 of lactation, the milk accumulation was clearly noticed in the mammary glands of some animals in the oxytocin injected groups and the average weight of mammary glands was greater in most of the oxytocin injected groups than in controls. These results indicate that exogenously administered oxytocin exerted an inhibitory effect on lactation in mice, possibly on the process of milk ejection.

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The newts, Cynops pyrrhogaster, that had been parathyroidectomized lived until they were sacrificed 989-1, 003 days after operation. The serum calcium was 7.8mg/100ml on an average of 4 animals observed, being significantly higher than the lowest level found 4-180 days after parathyroidectomy. As parathyroid glands are not regenerated, it may be concluded that they are not indispensable for the maintenance of the life of the newt.

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The amount of eel plasma cortisol was determined by the method of Van der Vies (1961) with some modification. The plasma cortisol level in the intact eels kept in either freshwater or seawater was about 4μg/100ml. Single intraperitoneal injection of ACTH caused a marked increase in the level of this substance after 2 hrs. In the hypophysectomized eel kept for ten days in freshwater, the cortisol concentration decreased to 0.3μg/100ml. Transfer of the intact eel from freshwater to seawater resulted in a significant increase in its concentration within 2 hrs., whereas significant increase was not observed when the eel was retransferred from seawater to freshwater. Moreover, the increase after transfer to seawater was not observed when the eel had previously been hypophysectomized. These data suggest that interrenal of the eel is under direct control of pituitary. Possible involvement of cortisol in the adaptation mechanism to seawater in the eel was discussed.

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