下垂体プロラクチン分泌に対する松果体の関与について

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For studying the relationship between the pineal gland and hypophysial prolactin (PRL) secretion, the experiment was done as follows : Exp. 1. The effect of a pinealectomy on serum and pituitary PRL levels. Adult female Wistar rats were divided into three groups. Group 1 : The rats underwent pinealectomy or a sham-operation by the Kuszak and Robin modified method 3 weeks after castration. They were sacrificed by decapitation 9 days after the pinealectomy. Group 2 : The rats underwent pinealectomy or a sham-operation 3 weeks after castration and were injected with estrogen-progesterone 1 week after the pinealectomy. They were sacrificed by decapitation 48 hrs after the injection. Group 3 : The rats underwent pinealectomy or a sham-operation on the 15-17th day of pregnancy. After delivery, on the third day post partum, the litter was separated to avoid the influence of suckling for 30 min, and they were sacrificed by decapitation. Exp. 2. The effect of melatonin, serotonin and arginine vasotocin (AVT) on serum and pituitary PRL levels. Melatonin, serotonin and AVT, in doses of 50,100 and 200μg, were injected i.v. into Group 2 and Group 3 described in Exp. 1. above. After the results of the preliminary experiment, the rats were decapitated at 30 min after the administration. The experimental conditions were as follows : room temperature; 22±2°C, light : dark; 12 : 12 hrs, maintained ad-libitum. The decapitations were done between 3 : 00 pm - 5 : 00 pm. Prolactin levels in the serum and pituitary were determined by radioimmunoassay. Pinealectomy made serum PRL levels increase significantly and pituitary PRL levels decrease significantly in the castrated (Group 1) and puerperal (Group 3) rats. On the other hand, serum PRL levels were significantly decreased by pinealectomy in the castrated estrogen-progesterone primed (Group 2) rats compared with the control rats (sham-operated). After the i.v. injection of melatonin 50μg, serum PRL levels deceased below preinjection levels in the pinealectomized rats of both Group 2 and Group 3. Namely, the serum PRL levels in the non pregnant rats were significantly more depressed. On the other hand, the serum PRL levels of the puerperal rats, increased by pinealectomy, were also depressed by a melatonin 50μg injection. In the sham-operated rats, both Group 2 and Group 3, a melatonin 50μg injection increased the serum PRL levels, especially in the puerperal rats (Group 3). On the other hand, the serum PRL levels did not decrease with AVT and serotonin injections in either group of pinealectomized rats. AVT administration made serum PRL increase greatly in the pinealectomized and sham-operated rats. There was no significant difference on the serum PRL increased by AVT between the pinealectomized and sham-operated rats. The hypophysial PRL levels were greatly increased by melatonin after a 50μg injection in the pinealectomized and sham-operated puerperal rats. These results of our experiments, judging by the changes in the levels of serum and pituitary PRL, may be elucidated as follows : a) In non pregnant rats, the pineal gland probably acts to stimulate PRL release by inhibiting hypothalamic PIF. On the other hand, in puerperal rats, the pineal gland probably acts to inhibit PRL release by inhibiting hypothalamic PRF. b) The physiological effect of melatonin on PRL secretion, within a physiological range of 50pg melatonin, will indicate the releasing and inhibiting action. The effect of melatonin on hypophysial PRL might be an inhibiting action, judging from the depressed serum PRL levels resulting from a 50μg melatonin injection into the pinealectomized rats. However, in the presence of the intact pineal gland, the PRL releasing effect of melatonin -possibly by releasing AVT in the pineal gland -might be superior to the PRL inhibiting effect of melatonin alone.
日本内分泌学会の論文

下垂体プロラクチン分泌に対する松果体の関与について

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