Host endocrine system

Effect on the Host Endocrine System. Several publications document an endocrine basis of several parasitoid-host interactions (18, 20, 49, 50). However, most of the mechanisms involving the endocrine interactions remain to be clarified. At best, we can describe the qualitative effects but not the regulatory factors responsible for the interactions. Until the characterization of... 

From this review we see that symbiotic viruses from the braconids and the ichneumonids have some differences in their physical structures and their apparent interaction with the host. Some variations noted in the action of these viruses may eventually be correlated with differences in viral structures and the interaction of the viruses with venom components. Certain host tissues may be susceptible to one virus-type and refractive to the other virus-type. It is possible that ichneumonids, which are commonly known as tissue feeders, contain symbiotic viruses that have a more prominent effect on the endocrine system of the host, thereby preserving the host tissue. In comparison, braconids, which... 

It thus appears that the suitability of a particular host stage and possibly different hosts may depend on the host s endocrine activity. However, the parasitoid also can have a profoimd effect on the host s endocrine system. 

Several lines of evidence indicate that macromolecules of as yet unidentified chemical nature, produced by cancers and released into the systemic circulation, are responsible for the biochemical alterations in the liver and other host organs. In view of the diverse regulatory properties of the many different enzymes that increase or decrease towards their immature level (see Table III), a deficiency or excess in any given endocrine or dietary factor can clearly not explain the phenomenon. Nor has it been possible to implicate reductions in the efficacy of these factors. Subnormal concentration of the nuclear thyroid hormone receptor has been noted in the liver of tumor-bearing animals(24) however, since losses in the T3-inducible catalysts of the same liver occurred at much earlier stages of tumor-bearing,(24) the subnormal receptor concentration could clearly not be the cause of these losses but was probably another, and rather late, reflection of the process of biochemical undifferentiation. 

Insects are so successful because of their mobility, high reproductive potential, ability to exploit plants as a food resource, and to occupy so many ecological niches. Plants are essentially sessile and can be seen to produce flowers, nector, pollen, and a variety of chemical attractants to induce insect cooperation in cross-pollination. However, in order to reduce the efficiency of insect predation upon them, plants also produce a host of structural, mechanical, and chemical defensive artifices. The most visible chemical defenses are poisons, but certain chemicals, not intrinsically toxic, are targeted to disrupt specific control systems in insects that regulate discrete aspects of insect physiology, biochemistry, and behavior. Hormones and pheromones are unique regulators of insect growth, development, reproduction, diapause, and behavior. Plant secondary chemicals focused on the disruption of insect endocrine and pheromone mediated processes can be visualized as important components of plant defensive mechanisms. 

Hormones of both synthetic and biological origin are known endocrine disruptors. The best known of these is diethylstilbesterol (DES), a synthetic estrogen that was prescribed by physicians to prevent spontaneous abortions in women from 1948 to 1971. Daughters of women who took DES have suffered a host of reproductive problems including a reduction in fertility, abnormal pregnancies, immune system disorders, periods of depression, and early onset of vaginal clear-cell adenocarcinomas and reproductive tract cancer. Known hormonal endocrine disruptors are listed in Table 4.5. 

Advances in molecular studies on mechanisms of cancer pathogenesis have led to the identification of a wide range of host factors that play important roles in the development of cancer. The majority of these molecules are the components of endocrine and immune systems that have become therapeutic targets for cancer [90, 96]. The most well-studied hormonal receptors, oestrogen receptor a. and [1 isoforms (ERa and ER/i), and their involvement in the progression of cancer, particularly breast cancer, were discovered more than three decades ago. ERjS expression predominates in normal breast tissue, being detected in 22% of... 

Whereas the task of chemotherapy is to rid the host of bacteria, viruses, fungi, protozoa, worms and insects, pharmacodynamics has a more difficult programme because the uneconomic cells are part of the organism of the economic species. For example, the uneconomic form may be an endocrine gland that has hypertrophied and upset the balance of metabolism of an otherwise healthy body it may simply be some part of the nervous system... 

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