ラット視床下部および下垂体のオキシトシン含量に関する研究

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One of the neurohypophyseal hormones, oxytocin, is known to have the biological activities of uterine contraction and milk ejection. Recently, serum levels of this hormone have been studied at several laboratories using the radioimmunoassay method, but reports dealing with the hypothalamic and pituitary regions where biosynthesis, storage and secretion take place, are rare. In this report, we will present the oxytocin content of the hypothalamus and hypophysis in Sprague-Dawley rats under various conditions, using a specific radioimmunoassay as previously reported. In brief, an anti-oxytocin serum was made by immunizing New Zealand white rabbits with an oxytocin-bovine serum albumin complex, using Freunds' complete adjuvant. The antiserum was diluted to 1 : 9,000 for use in the radioimmunoassay. The chrolamine T method was used with some modifications for labelling 125I to synthetic oxytocin, and the double antibody technique was used for separation of B/F hormones. In this assay system, the cross-reactivities of Arg-vasopressin and Lys-vasopressin were negligible, and the recovery rate was 102.5 ± 18.4% (mean ± S.D.). The values of the inter-assay coefficient of variation were less than 13.6%, and those of the intra-assay coefficient of variation were less than 7.5%. Under ether anesthesia, the rats were decapitated, and the hypothalamus and hypophysis were removed. Isolated tissues were homogenized immediately with 2 ml of a 0.05 M phosphate buffer pH 7.5 containing 0.1M EDTA and orthophenanthroline under ice cold conditions. After overnight extraction at 4°C, the homogenate was centrifuged at 4°C for 20 minutes at 3,000 rpm. A sample of the supernatant was measured by radioimmunoassay, and the following results were obtained : 1) Dilution curves of the hypothalamic and pituitary extracts showed a parallel relation with the standard curve of synthetic oxytocin, and the same elution profiles were observed between these extracts and the synthetic oxytocin on a Sephadex G-25 column chromatography (1.2 X 90cm). From these results, the immunoreactive substance presented in the hypothalamic and pituitary extracts was considered to be the same molecule as synthetic oxytocin. 2) Oxytocin contents of the hypothalamus in male and female adult rats were 2.14 ± 0.59, 1.57 ± 0.32 mU/rat, respectively (mean ± S.D., n=10), and those of the hypophysis were 197.4 ± 30.7,169.2 ±18.2 mU/rat, respectively (mean ± S.D., n=10). There were no statistically significant differences between male and female rats in either tissue. 3) Pituitary oxytocin was measurable as early as the 4th day after birth; it then showed a marked increase with growth. Sexuality caused no difference at any age tested. 4) Hypothalamic oxytocin contents in pregnant rats showed a significant increase on the 3rd day of gestation (3.59 ± 0.79 mU/rat, n=10, p<0.001), as compared with nonpregnant levels, then gradually decreased towards the delivery date and reached minimum levels at the 20th day of gestation (1.29 ± 1.04 mU/rat, n=10). On the 4th day of postpartum, they increased again to the level of 2.75 ± 0.72 mU/rat (mean ± S.D., n=6), which was significantly higher than the nonpregnant levels (p<0.01). 5) Pituitary oxytocin contents in pregnant rats increased continuously from the 3rd day of gestation (377 ± 47.5 mU/rat, n=10) to the delivery date and reached maximum levels at the 20th day of gestation (492 ± 95.7 mU/rat, n=10). On the 4th day of postpartum, they remained at still higher levels (269 ± 62.9 mU/rat, n=6) than the nonpregnant levels. 6) Exogenously administered estradiol (50,100μg) or estradiol (100μg) with progesterone (25 mg) could not change the oxytocin content of either the hypothalamus or hypophysis in castrated or noncastrated rats.
日本内分泌学会の論文

ラット視床下部および下垂体のオキシトシン含量に関する研究

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