Hormonal controls effects

Basically growth hormones alter the normal growth of some insect species. The juvenile growth hormone worked effectively to kill some insects in the laboratory, but when applied in the field for pest control, the hormone was not effective. Its problems centered on its high cost, rapid rate of breakdown after application, and its broad spectrum effects. For example, the hormone was found to kill beneficial species as well as pest species, much like insecticides. Thus far, it has not proven to be a useful technology for pest control (42). 

Hormones have a profound effect on carbohydrate metabolism. Great interest has been aroused by reports of hormonal control of hexokinase activity by specific proteins in animal tissues.99- 100 Hexokinase action is the rate-limiting step in the uptake of D-glucose by muscle. Hexokinase is inhibited in diabetic muscle, but the inhibition can be partially reversed by insulin. A protein fraction from the anterior pituitary gland will inhibit the hexokinase of extracts of brain and muscle, and the effect of this... 

V) The validity of RIA entirely depends upon the identical behaviour of standard and labelled substance unknown, and not on the identity of the labelled tracer and the unknown. Hence, the experimental conditions of incubation of standards and unknowns must be identical for any factors that might affect the extent of the immunochemical reaction, pH, ionic composition, protein content or any other substances of interest. However, these conditions may be tested conveniently and can be controlled effectively by preparing standards in hormone free plasma at the same dilution at which unknowns are assayed. 

Cooper R, Chadwick R, Rehnberg G, Goldman J (1989) Effect of lindane on hormonal control of reproductive function in the female rat. Tox Appl Pharm 99 384-394 Cooper RL, Stoker TE, Goldman JM, Parrish MB, Tyrey L (1996) Effect of atrazine on ovarian function in the rat. Reprod Toxicol 10 257-264... 

In grouped female mice ovulation and estrus are suppressed (Champlin, 1971) and pseudopregnancies occur (van der Lee and Boot, 1955). The odor of crowded female mice (eight per cage) inhibited ovulation in other females. The hormonal control of this effect has been difficult to explain. Early studies indicated that ovariectomized mice were not able to inhibit other females but in other studies, ovariectomized females still inhibited estrus in other females (Marchlewska-Koj, 1990). 

In rats ammonium perfluorooctanoate induced hepatomegaly that was more pronounced in the male than in the female. Male rats are thought to be more sensitive to the toxic effects of ammonium perfluorooctanoate because of their slower excretion rate. The rapid excretion by female rats is due to active renal tubular secretion, which is considered to be hormonally controlled by estradiol and testosterone levels. The hepatomegaly was hypertrophic rather than hyperplastic and involved proliferation of peroxisomes. 

Autonomic and hormonal control of cardiovascular function. Note that two feedback loops are present the autonomic nervous system loop and the hormonal loop. The sympathetic nervous system directly influences four major variables peripheral vascular resistance, heart rate, force, and venous tone. It also directly modulates renin production (not shown). The parasympathetic nervous system directly influences heart rate. In addition to its role in stimulating aldosterone secretion, angiotensin II directly increases peripheral vascular resistance and facilitates sympathetic effects (not shown). The net feedback effect of each loop is to compensate for changes in arterial blood pressure. Thus, decreased blood pressure due to blood loss would evoke increased sympathetic outflow and renin release. Conversely, elevated pressure due to the administration of a vasoconstrictor drug would cause reduced sympathetic outflow, reduced renin release, and increased parasympathetic (vagal) outflow. 

Hormonal control of mating behaviour is well documented in animals. In rats, estrogen and, to a lesser extent, progesterone control lordosis behaviour via the central nervous system (CNS). In female non-human primates, attractiveness and proceptivity change during the menstrual cycle or as a result of sex steroid administration. The effects of hormones on receptivity are unclear. It is assumed that steroid hormones influence behaviour in humans as they do in animals however, it is difficult to differentiate the effects of social and other environmental factors from the effects of sex steroids on mating behaviour in humans. 

Ecdysone stimulates the synthesis of RNA in tissues. Visual demonstration of the effect is provided by its action on polytene chromosomes of fly larvae (Fig. 26-14).361 Fifteen minutes after the application of ecdysone, a puff is induced on one band of the chromosome a second puff forms at a later time while a preexisting puff diminishes. Thus, like steroid hormones in mammals, ecdysone appears to have a direct controlling effect on transcription. The cuticle-shedding process (ecdysis) is initiated by the brain peptide eclosian. However, the brain may be responding to the ecdysis-triggeiing hormone, a peptide that is secreted by a series of epitracheal glands located in various segments of the body.362... 

Endocrine and Reproductive Effects. Because the male and female reproductive organs are under complex neuroendocrine and hormonal control, any toxicant that alters any of these processes can affect the reproductive system (see Chapters 17 and 20). In addition metals can act directly on the sex organs. Cadmium is known to produce testicular injury after acute exposure, and lead accumulation in the testes is associated with testicular degeneration, inhibition of spermatogenesis, and Leydig-cell atrophy. 

Tebufenozide acts by mimicking the effects of the insect hormone ecdysone, which along with juvenile hormone, controls the initiation of a molt. Exposure to tebufenozide induces a premature molt that traps the insect in its old cuticle. This compound is especially effective against caterpillars. 

At this point the history of the concept of hormonal control of insects should be recalled, since the major reasons for the selection of JH as a rational lead for pesticide design were the beliefs that JH occurred only in insects and not in other animals. The implication was that JH would therefore be selectively active in insects with no significant effects on other forms of life. In the cases of JH analogs of the farnesane skeleton, extensive studies of comparative toxicology have largely verified these beliefs. Toxicological results have been reviewed in detail (20 ) and a comprehensive study of the environmental fate and metabolism of methoprene has been completed (2 1). ... 

Physiologically, hormones are responsible for maintaining a steady state— homeostasis—in the human being, and help the organism to cope with environmental changes that affect it. Hormones control enzymatic activities this effect is... 

The transport of cholesterol to, and its side-chain cleavage in, the mitochondria are the most important steps in the hormonal control of steroidogenesis. The enzymatic activities in the endoplasmic reticulum are also under hormonal control. However, expression of hormonal effects in this compartment requires several hours and is therefore part of the chronic, trophic effects of LH [3,4,32],... 

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