This project was undertaken in order to elucidate two important problems in Thyroid Biochemistry namely, the kinetics of labelling of tyrosine and monoiodotyrosine (MIT) and the pathways of synthesis of triiodothyronine (T3 ) and thyroxine (T4 ).

No description available.

Certain aspects of the biochemistry of the thyroid gland have been studied. The techniques of filter paper chromatography and radioautography were used to separate and identify the iodine-containing amino acids of the gland, and were modified somewhat, in order to obtain reliable results. Although a series of preliminary experiments were performed with the thyroid glands of rats in vivo, the main part of this work made use of the in vitro technique. Surviving tissue slices were incubated in the presence of the radioactive tracer, iodine131. Evidence was obtained which indicated that at least two of the amino acids found "free" in the thyroid gland were degraded by the gland to inorganic iodide. The mechanism of action of a number of thyroid gland inhibitors was investigated. It was found that all but two of the materials studied led to the formation in the tissue slices of unidentified iodine—containing materials with the simultaneous disappearance of inorganic iodide. Hence, at least a part of the goitrogenic nature of these inhibitors would appear to be due to the "removal" of iodide. It was found chat one portion of the inhibition caused by 3 - fluorotyrosine could be "reversed" in vitro with tyrosine, interesting sex variations in thyroid gland activity were observed during these experiments. / Thesis / Master of Science (MSc)

Presented as Thesis (Ph. D.)--University of Wisconsin--Madison, 1930. / Cover title. Reprinted from Physiological zoölogy, vol. IV, no. 1 (Jan. 1931). Includes bibliographical references (p. 55, 57).

Diss. (sammanfattning) Göteborg : Göteborgs universitet, 2009. / Härtill 6 uppsatser.

Thesis (M.S.)--University of Michigan, 1971.

Thesis (M.S.)--University of Michigan, 1971.

Thesis--Catholic Univ. of America.

The timing of seasonal events in salmonids is thought to be controlled by endogenous circannual rhythm(s) which are entrained by the seasonally-changing daylength. This thesis investigates the role of the pineal gland in the perception of the photoperiodic zeitgeber and the subsequent transmission of this information to the brain through neural or hormonal pathways. Melatonin biosynthesis by isolated rainbow trout pineal glands was shown to exhibit a differential response to graded photic or thermal stimuli. In vitro experiments were carried out at 10±0.50 C as this provided optimum melatonin levels for radioimmunoassay analysis together with a pineal longevity of up to 14 days. By incorporating a variety of light intensities into the light/dark cycle, the salmonid pineal gland was shown to synthesise significantly different levels of melatonin even when light levels varied by only 0.5 lux. Early work on the salmonid pineal suggested it was unresponsive to red light, having a spectral sensitivity which peaks between 500 and 550 nm, this study has revealed that the pineal is also capable of responding to wavelengths between 660 to 800 nm, at which pineal reception was previously thought to be severely limited. No endogenous rhythm of melatonin secretion was observed within the isolated rainbow' trout pineal gland. Both Atlantic salmon and Atlantic halibut pineals exhibited elevated levels- of melatonin in response to the dark phase, however, they also appeared capable of maintaining this rhythm in the absence of external stimuli. This provides the first evidence that the daily rhythm of melatonin production in these species is controlled by an endogenous circadian oscillator located within the pineal II gland. The pinealectomy technique developed during the course of this thesis successfully abolished the diel rhythm of melatonin secretion and, together with an enucleation procedure, enabled the pineal to be identified as the predominant source of the dark phase melatonin in Atlantic salmon and rainbow trout. However, the lateral eyes did contribute significantly to plasma melatonin levels in both species. Long term experiments, involving pinealectomy and/or implantation of melatonin, were used to investigate the role of the pineal gland in the timing of rainbow trout maturation and smoltification in Atlantic salmon. Pineal removal at the summer or winter solstices did not significantly alter the timing of smoltification. However, significantly higher blood serum osmolarities following seawater challenge tests were observed in smolts implanted with melatonin. This, together with a significant growth increase shown by salmon parr within 1 month of implantation, indicates that melatonin may directly affect the development of salmonids through either a physiological response or by influencing the entrainment of endogenous rhythms. The increased growth observed in the implanted parr is also thought to be responsible for the unimodal population distribution and high percentage of S1 smolts within this group. Investigations into the role of the pineal gland in the timing of spawning in rainbow trout found that pineal removal at the summer solstice caused a 6 week delay in spawning time compared to intact fish. However, no clear effects on spawning time were observed when pineal removal, with or without melatonin implantation, was performed to coincide with the change from long to short daylengths which is known to advance spawning times. Although no significant effect in spawning times was observed between groups, the 4 month spawning period of the pinealectomised group compared to 1 month in the shampinealectomised fish also suggested that pineal removal may have caused a desynchronisation in spawning time. Pinealectomy and/or implantation did not alter egg size or fecundity, but plasma calcium levels were shown to be significantly lower in the pinealectomised trout over the spawning period. To summarise, the pineal gland and melatonin play a significant role in salmonid development. It is suggested that melatonin can influence biological systems through a direct physiological action while the pineal gland may synchronise circannual events through the photoneuroendocrine transduction of seasonal environmental information.

The physiological effects of the pineal gland on the prolactin cells of the adenohypophysis were examined in short photoperiod-exposed male hamsters, as well as in blinded male and female hamsters. Pituitary storage of prolactin was assessed by monitoring radioimmunoassayable prolactin levels in the pituitaries in vivo and the total amount of immunoreactive prolactin in vitro. The effects of the pineal on prolactin secretion were estimated by measuring immunoassayable prolactin titers in the serum. Prolactin synthesis was measured by the ability of anterior pituitaries to incorporate ³H-leucine into prolactin in vitro. Finally, the effects of blinding and the activated pineal on hypothalamic hypophysiotrophic activity was assessed by incubating pituitaries in the presence of neutralized, acidic extracts of the stalk-medium eminence (SME) region of the mediobasal hypothalamus. In the male hamster, the pineal gland inhibits PRL cell function which encompasses reductions in the synthesis, storage and release of prolactin. The depressions in prolactin release and in pituitary storage are evident as early as three weeks after males are deprived of light. However, the inhibitory influence of the pineal on prolactin synthesis may be only partially apparent by eight to nine weeks after male hamsters are deprived of light, and is not fully evident until 12 weeks of light restriction. In the blinded female hamster, the synthesis, storage and release of prolactin are also markedly suppressed. However, all aspects of prolactin cell inhibition in the female may not be pineal-mediated. Furthermore, it appears that there may be some direct hypothalamic mechanism by which orbital enucleation inhibits prolactin cell function that is independent of the pineal gland. Based on the data presented in this dissertation, it is concluded that the SME region of the female hamster contains inhibitory activity which may be specifically responsible for the inhibition of prolactin synthesis. Furthermore, blinding and the pineal gland may independently exert rather specific influences upon hypophysiotrophic activity within the SME region of the female hamster.