Endogenous hormon level

In the circumstances, there is no need for an exhaustive discourse on all aspects of plant hormone analysis here. Instead, the main techniques currently employed for quantitative analysis will be discussed, along with HPLC-MS and procedures that are used to investigate the metabolism of plant hormones. Where appropriate, reference will be made to molecular biology studies that have either investigated aspects of plant hormone metabolism and/or estimated endogenous hormone levels. 

Endogenous hormone levels however can be considered as major factors in determining the specificity of cellular responses to these rather general stress stimuU (Feher et at, 2003). The temporal and spatial changes in endogenous auxin levels are important factors controlling the embryogenic cell fate (Feher et at, 2003). 

One of the most unnecessary failings in hormone analysis has been a paucity of effort to correlate endogenous hormone levels with quantitative measures of development to establish a relationship or lack of one. Thus, an important aspect in the analysis of hormonal control carries some interpretative difficulties, yet the two approaches outlined plus bits and pieces of other types of evidence described below have given enough data to understand at least parts of some hormonal control systems. 

Itai C, Ben-Zioni A, Ordin L (1973) Correlative changes in endogenous hormone levels and shoot growth induced by short heat treatments to the root. Physiol Plant 29 355-360... 

Digby J, Wareing PF (1966 a) The effect of applied growth hormones on cambial division and the differentiation of the cambial derivatives. Ann Bot 30 539-548 Digby J, Wareing PF (1966 b) The relationship between endogenous hormone levels in the plant and seasonal aspects of cambial activity. Ann Bot 30 607-622 Esau K (1965) Vascular differentiation in plants. Holt, Rinehart and Winston, New York... 

Measurement of contaminants in fish has concentrated on muscle tissue since the aim has generally been to protect the health of the consumer rather than that of the fish. Endocrine tissue such as the gonads has been much more rarely examined, while data for adrenal, thyroid and pituitary levels are virtually non-existent. More data are available for the liver, as a lipid rich tissue and the major site of xenobiotic catabolism, but the concentrations have rarely been related to its capacity to produce vitellogenin or metabolise endogenous hormones. Tissue concentrations of a wide range of chemicals, are at a level which suggests that, either alone or in combination, they will cause significant endocrine disruption in fish in many polluted habitats. 

The term endocrine disrupter (ED) has tended to be used for those chemicals which act specifically at the level of the hormone receptor present in the target cells of various organs. Such chemicals may either mimic the action of the natural hormone (agonistic activity) or are sufficiently similar in molecular shape to the naturally produced hormone to interfere with the interaction between the hormone and receptor, thus blocking or impeding the activation of the receptor (antagonsitic activity). Such effects may occur at very low concentrations (as with the endogenous hormone), compared with the concentrations normally required to elicit the more traditional toxic effects attributed to chemicals. Recently,... 

Patients with mild or subclinical hypothyroidism do not need to be started on the full replacement dose because they still have some endogenous hormone production. Start these patients on 25 to 50 meg/day, and titrate every 6 to 8 weeks based on TSH levels. Over time, it is likely that the LT4 dose will need to be increased slowly as the patient s thyroid gland loses residual function. 

Non-sex accessory tissues also are targets for the protein anabolic actions of androgens. These tissues possess lower levels of endogenous hormone, minimal 5a-reductase activity, and lower concentrations of specific androgen receptors. The protein anabolic actions are probably mediated by an interaction with the androgen receptor. 

Calcitonin derived from synthetic sources can be administered to mimic the effects of the endogenous hormone. As described previously, endogenous calcitonin decreases blood calcium levels and promotes bone mineralization. Consequently, synthetically derived calcitonin is used to treat hypercalcemia and to... 

Xenobiotics have the ability to disrupt hormone activity through a variety of mechanisms, though the predominant mechanisms appear to involve binding to the hormone receptor, either as an agonist or antagonist, or by modulating endogenous steroid hormone levels. 

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