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Role of the pituitary in the high thermal resistance of the goldfish, Carassius auratus L. Johansen, Peter Herman


Goldfish were hypophysectomlzed and subsequently treated, with luteinizing, thyrotropic, adrenocorticotropic and lactotropic (prolactin) hormones; likewise some fish were treated with crude salmon pituitary extract. It was found that, hypophysectomized goldfish had a lower heat, resistance than normal fish, and that replacement therapy using these hormones produced no statistically significant effect on the heat resistance of hypophysectomized fish. Experiments were undertaken in which fish were subjected to either a long or short photoperiod. The results for the photoperiod manipulations were not always statistically significant at the 0.05 level, but there was always the suggestion that fish with intact pituitaries under the 16 hour photoperiod were more heat resistant than fish held under an 8 hour photoperiod. Experiments were carried out in which the pituitary was autotransplanted into the musculature of the caudal peduncle. Fish so treated had a heat resistance like that of pituitary intact 16 hour photoperiod fish while hypophysectomized fish had a heat resistance like that of pituitary intact 8 hour photoperiod fish. From a study of the endocrine (target) organs of these animals it is concluded that the autotransplanted pituitary secretes thyrotropic hormone in supernormal amounts, adrenocorticotropic hormone in subnormal amounts gonadotropic hormone not at all and prolactin in at least normal amounts. Based on information in the literature it seems that growth hormone is secreted in very small amounts by the transplanted pituitary. From all these experiments it is concluded that the pituitary is involved in heat resistance. It is suggested that it must be located in its normal position, for a photoperiod effect. By combining the histological information with the heat resistance results of the pituitary autotransplant experiments it is suggested that growth, gonadotropic, thyrotropic and adrenocorticotropic hormones play no major role in heat resistance. It is suggested that prolactin is the hormone most directly concerned with the heat resistance of goldfish; this hormone may also be involved in the photoperiod induced change in heat resistance.

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