| Research Abstract |
Endocrinological analysis of biological phenomena such as metamorphosis, growth and reproduction in amphibian life cycle were performed. 1)Metamorphosis Amphibian metamorphosis is mainly under the control of three hormones, namely, thyroid hormone, adrenocortical hormone and prolactin. Our study was focused on prolactin gene expression during metamorphosis. Using bullfrog and toad prolactin cDNA, we have revealed that prolactin mRNA levels rise as metamorphosis progresses. This indicates that the elevation of plasma and pituitary prolactin levels during metamorphic climax accompanies the elevation of prolactin synthesis. The enhacement of prolactin cell function in the pituitary during metamorphic climax is presumed to be related with the maturation of adult organs which develop in this period. In fact, we have demonstrated that prolactin increases phospholipids in the lung surfactant. 2)Growth We have purified amphibian growth hormone from the bullfrog pituitary. Using this preparatio
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n, primary structure of amphibian growth hormone was determined. Homologous radioimmunoassay system was also developed. It was revealed that growth hormone levels rise as metamorphosis progresses and reaches maximum when the animals completed metamorphosis. Growth hormone mRNA levels are also high in the juvenile frogs. This indicates that in juveniles a marked growth occurs. As regards the mode of action of growth hormone, presence of a growth hormone mediator in the plasma, as in the case in mammals, was demonstrated in Xenopus. 3)Reproduction Hormonal control of courtship behavior in the newt, Cynops pyrrhogaster was studied. Sexually mature male of this species vibrates the tail in front of sexually mature female at the initial stage of courtship. It was reveled that both incidence and frequency of the tail vibration behavior are enhanced by prolactin and androgen (testosterone or dihydrotestosterone). Moreover the male releases a sex attractant into the water. It was revealed that the attractant is secreted from the abdominal glands of the cloaca. The development of the abdominal glands is also under the control of prolactin and androgen. It was demonstrated that this attractant is a peptide of molecular weight below 5,000. Less
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