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- Author: Allan J Gunn x
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Graham Centre for Agricultural Innovation, Wagga Wagga, New South Wales, Australia
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Graham Centre for Agricultural Innovation, Wagga Wagga, New South Wales, Australia
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School of Animal & Veterinary Sciences, Charles Sturt University, Wagga Wagga, New South Wales, Australia
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The control of reproductive processes involves the integration of a number of factors from the internal and external environment, with the final output signal of these processes being the pulsatile secretion of gonadotrophin-releasing hormone (GnRH) from the hypothalamus. These factors include the feedback actions of sex steroids, feed intake and nutritional status, season/photoperiod, pheromones, age and stress. Understanding these factors and how they influence GnRH secretion and hence reproduction is important for the management of farm animals. There is evidence that the RF-amide neuropeptide, kisspeptin, may be involved in relaying the effects of these factors to the GnRH neurons. This paper will review the evidence from the common domestic animals (sheep, goats, cattle, horses and pigs), that kisspeptin neurons are (i) regulated by the factors listed above, (ii) contact GnRH neurons and (iii) involved in the regulation of GnRH/gonadotrophin secretion.
Gulbali Institute, Charles Sturt University, Wagga Wagga, NSW, Australia
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Gulbali Institute, Charles Sturt University, Wagga Wagga, NSW, Australia
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Gulbali Institute, Charles Sturt University, Wagga Wagga, NSW, Australia
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Our previous studies showed that microinjection into the median eminence of the sheep of glucagon-like peptide- 1 (GLP-1) or its receptor agonist exendin-4 stimulates luteinising hormone (LH) secretion, but it is unknown whether the same effect may be obtained by systemic administration of the same. The present study measured the response in terms of plasma LH concentrations to intravenous (iv) infusion of exendin-4. A preliminary study showed that infusion of 2 mg exendin-4 into ewes produced a greater LH response in the follicular phase of the oestrous cycle than the luteal phase. Accordingly, the main study monitored plasma LH levels in response to either 0.5 mg or 2 mg exendin-4 or vehicle (normal saline) delivered by jugular infusion for 1 h in the follicular phase of the oestrous cycle. Blood samples were collected at 10 min intervals before, during and after infusion. Both doses of exendin-4 increased mean plasma LH concentrations and increased LH peripheral pulse amplitude. There was no effect on inter-pulse interval or timing of the preovulatory LH surge. These doses of exendin-4 did not alter plasma insulin or glucose concentrations. Quantitative PCR of the gastrointestinal tract samples from a population of ewes confirmed the expression of the preproglucagon gene (GCG). Expression increased aborally and was greatest in the rectum. It is concluded that endogenous GLP-1, most likely derived from the hindgut, may act systemically to stimulate LH secretion. The present data suggest that this effect may be obtained with levels of agonist that are lower than those functioning as an incretin.
