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Changes in the hypothalamic-hypophyseal axis of mares in relation to the winter solstice

, : Changes in the hypothalamic-hypophyseal axis of mares in relation to the winter solstice. Journal of Reproduction & Fertility 96(1): 195-202

In mares, the amount of gonadotrophin-releasing hormone (GnRH) is low in the hypothalamus during seasonal anoestrus, but by early spring, concentrations of GnRH are high. The timing of this response was characterised more precisely by determining concentrations of GnRH in hypothalamic tissue collected immediately before and at various times after the winter solstice (22 December 1986). Ovaries, pituitary gland, hypothalamus and a blood samples were collected from six groups of mares (6-12 mares per group) at death, 1 week before day of the winter solstice and 1, 2, 3 and 12 weeks afterwards. No significant changes in weight of the interior pituitary gland or concentration of luteinizing hormone (LH) and (FSH) were observed in the anterior pituitary gland (P lt 0.1). Mean diameter of the largest follicle, number of follicles gtoreq 20 mm in diameter and concentrations of LH and FSH in serum remained unchanged for weeks -1 to +3 (P gt 0.05), then increased significantly by week 12 (P lt 0.001). Content and concentration of GnRH in the median eminence was low at -1 week, increased gradually (P lt 0.05) to a maximum by +1 week, then decreased gradually (P lt 0.05) to low values at 12 weeks. Means (+- SEM) for -1, +1 and +12 weeks were 33.5 +- 5.5, 117.7 +- 18.6 and 29.8 +- 3.7 ng GnRH, respectively. Mean content of GnRH in the preoptic area of the hypothalamus showed a reciprocal pattern. Since content of GnRH in the median eminence was increasing on the day of the winter solstice, the impetus for resurgence of GnRH synthesis may not be lengthening photoperiod, but refractoriness to the previous short photoperiod. Increased gonadotrophin content observed at 12 weeks suggest that the coincidental reduction in content in GnRH may be due to an increase in secretion. One role of lenthening photoperiod may therefore by to boost production of GnRH during a period of increasing release.

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Yoshioka, H.; Kurisu, K.; Arita, K.; Tominaga, A., 1998: A case of non-functioning pituitary adenoma accompanied by a large cyst. Acta Neurochirurgica. 140(3): 293-294

Tourrel, Cecile; Bailbe, Danielle; Meile, Marie Jo; Kergoat, Micheline; Portha, Bernard, 2001: Glucagon-like peptide-1 or exendin-4 treatment limited to the pre-diabetic period limits the progression to overt NIDDM in the adult GK rat. Diabetes 50(Supplement 2): A339, June

Watt A.D., 1989: The chemical composition of pine foliage in relation to the population dynamics of the pine beauty moth panolis flammea in scotland uk. This paper reports part of a study to determine why damaging outbreaks of the pine beauty moth, Panolis flammea (D and S) (Lepidoptera: Noctuidae), in Scotland are frequent on lodgepole pine but do not occur on scots pine, and why outbreaks on lod...

Wolf E.; Mallozzi A.; Rodis J.F.; Campbell W.; Mead J.; Vintzileos A.M., 1991: A 10 year review of preterm birth of twins at a referral tertiary care center. American Journal of Obstetrics & Gynecology 164(1 PART 2): 378

Kurahashi M.; Inomata K., 1990: Amylase activity and starch digestion in the gastrointestinal tract of pancreatic exocrine insufficient rats. Japanese Journal of Physiology 40(SUPPL): S84

Morabia, Alfredo; Abel, Thomas, 2003: International comparison of health determinants: Let's move on to the next step. Sozial und Praeventivmedizin 48(2): 77-78

Schreier, J., 1975: Utilization of absorbed nutrients for yield formation in poppy at the start of flowering. Assessment of the results of inorganic analyses of 60 samples of above-ground DM of poppy cv. Azur at the start of flowering in field trials in 1963-5 showed that the mean concentration of nutrients in the DM was 2655 mg N, 635 mg P, 3933 mg K, 20...

Hodges, J. R., 1953: Synergic effects of amylobarbitone sodium and ethanol. Amylobarbitone and ethanol acted synergistically in producing toxic and anesthetic effects in mice. Graphic treatment of the results revealed that the effects of these 2 drugs were simply additive and no evidence was obtained as to a potentiation...

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Moucha, J., 1969: Tribus Haematopotini (Diptera, Tabanidae). Acta ent. Mus. natn. Pragae, 23: 213-235