Possible direct induction by estrogen of calcitonin secretion from ultimobranchial cells in the goldfish.
The plasma level of calcitonin (CT), a calcium (Ca)-regulating hormone, is known to increase in female teleosts during the reproductive period. In the present study, a correlation between plasma CT and Ca and one between plasma CT and the gonad somatic index were demonstrated in the female goldfish but not in the male. To clarify the relationship between CT and Ca, we examined the plasma CT and Ca levels after injecting immature goldfish with estrogen. At day 1, the plasma CT level significantly increased, whereas the plasma Ca level was not changed from its initial level. This result suggests that the trigger of CT secretion is estrogen and that estrogen directly acts on the ultimobranchial gland (UBG), a CT-secreting organ. To determine whether the UBG is equipped with estrogen receptor (ER), an ER binding assay and immunohistochemical staining of UBG cells with an antibody against ER were conducted. As a result, estrogen-specific binding (Kd, 18.52 nM; Bmax, 1.35 pmol/mg protein) and ER-immunoreactivity in the UBG were demonstrated. Furthermore, the expression of alpha, beta, and gamma types of ER in the UBG was also detected by use of the reverse-transcription polymerase chain reaction. Thus, we concluded that estrogen acts on the UBG to induce the release of CT, which in turn plays an important role in reproduction directly and/or indirectly through Ca. This is the first report on the existence of ERs in a teleost UBG and the occurrence of CT secretion caused by estrogen.
Noto Marine Laboratory, Institute of Nature and Environmental Technology, Kanazawa University, Uchiura, Ishikawa 927-0553, Japan. nobuo@kenroku.kanazawa-u.ac.jp
Nobuo
N
Suzuki
Kazutoshi
K
Yamamoto
Yuichi
Y
Sasayama
Tohru
T
Suzuki
Tadahide
T
Kurokawa
Akira
A
Kambegawa
Ajai K
AK
Srivastav
Shinji
S
Hayashi
Sakaé
S
Kikuyama
D000818:Animals; D002116:Calcitonin / Q000097:blood / Q000378:metabolism*; D002118:Calcium / Q000097:blood; D004958:Estradiol / Q000502:physiology*; D005260:Female; D006054:Goldfish / Q000254:growth & development / Q000378:metabolism*; D007150:Immunohistochemistry; D008297:Male; D009929:Organ Size; D010053:Ovary / Q000254:growth & development; D011897:Random Allocation; D011960:Receptors, Estrogen / Q000378:metabolism*; D012098:Reproduction / Q000502:physiology; D012737:Sex Factors; D012741:Sexual Maturation / Q000502:physiology; D014460:Ultimobranchial Body / Q000166:cytology / Q000378:metabolism*
D011960:Receptors, Estrogen; D004958:Estradiol; D002116:Calcitonin; D002118:Calcium