The effect of cholecystokinin (CCK)-8 was studied on the release of luteinizing hormone (LH) from perifused medial basal hypothalami (MBH) and/or adenohypophyses of castrated bulls in a sequential double chamber perifusion system. LH concentrations in the perifusion efflux from the pituitary in series with the hypothalamus decreased significantly (P<0.05) after perifusion of 10-8M CCK as compared with control levels. In the similar perifusion LH concentrations in the efflux from the pituitary alone decreased significantly (P<0.01) after perifusion of 10-8M CCK. 10-7M CCK induced neither inhibitory nor stimulatory effects in perifusions of the pituitary in series with the hypothalamus except one fraction. Similarly, 10-7M CCK failed to induce a significant change in LH release in perifusion of the pituitary alone. LH concentrations in the perifusion efflux from pituitary in series with the hypothalamus increased significantly at 50 and 60 min after the initiation of 10-6M CCK perifusion as compared with the control level (P<0.05). LH concentrations in the efflux from the pituitary alone increased significantly 40, 50, 60 and 80 min after the initiation of perifusion with 10-6M CCK. The results indicate that CCK acts directly on the adenohypophysis to modulate release of LH in cattle.
The effects of the oral contraceptive on the pituitary content and plasma level of LH and the hypothalamic LH-RH level were investigated in 16 adult female rabbits. The oral contraceptive preparation, Sophia-C (Norethindrone 2mg + Mestranol 0.1 mg), as administered orally by a stomach tube each day for 7 days in 8 adult female rabbits. At the end of the treatment, the rabbits were bled from the abdominal aorta into heparinized syringes and the plasma was separated. The stalk median eminences were excised. All the materials were stored in -80 degrees C until assayed. Plasma level and the pituitary content of LH and the hypothalamic LH-RH were measured by radioimmunoassay. All the dose response curved were drawn using logitlog transformation. Radioimmunoassay procedures for LH was described in detail elsewhere. Purified rabbit LH for iodination (125-I) and strandard were prepared by T. Makino and R.O. Greep, at Research Laboratories for Human Reproduction, Harvard Medical School, Boston, U.S.A. The starting B/T was 25% at the final dilution of the antibody of 1/20,000. Minimal detectable quantity was about 40 pg/tube. The 50% intercepts were approximately 460 pg/tube. Radioimmunoassay procedures for LH-RH were performed according to the method described by Arimura et al. Antiserum against synthetic LH-RH was kindly supplied to us by Drs. A. Arimura and A.V. Schally, New Orleans, U'S.A. The synthetic LH-RH was kindly supplied to us by Dr. N. Yanaihara. The starting B/T ratio was 29% at the final dilution of the antibody of I/17,500. Minimal detectable quantity was about 40pg/tube and the 50% intercepts were 150pg/tube. It has been assumed that oral contraceptive drugs exert their action by blocking the hypothalamic LH-RH, resulting in a depression of the plasma level of LH, because plasma level of LH returned to the normal level when LH-RH was administered intravenously even while oral contraceptive steroids were given continuously. However, these findings concerning the site of action of the drugs furnished only indirect evidences. The possibility of a direct inhibitary effect of these steroids on the anterior pituitary cannot be ruled out. Administration of 2mg of Norethindrone and 0.1mg of Mestranol significantly depressed both the pituitary content and the plasma level of LH. On the other hand, they significantly increased the hypothalamic LH-RH level. Those findings strongly suggested the direct action of this drug on the anterior pituitary in the female adult rabbits. Detailed mechanisms on how the hypothalamic LH-RH was increased were not known in this experiment, further investigations are now in progress.
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