title: Central metabolic messengers and the effects of nutrition on gonadotrophin secretion in sheep.
abstract: Nutrition influences the reproductive axis via alteration of gonadotrophin secretion. However, a link between nutrition and the secretion of GnRH, which drives the axis, has yet to be established. The aim of the present study was to measure the change in the concentrations of metabolic substances in the cerebrospinal fluid of adult male sheep offered a diet designed to maintain constant gonadotrophin secretion (Group M; n = 6), or a diet known to increase gonadotrophin secretion (Group M + L; n = 6). On days 1, 3 and 10 of the dietary treatments, cerebrospinal fluid and jugular blood were sampled and analysed for metabolic fuels (glucose, amino acids and free fatty acids) and metabolic hormones (insulin, insulin-like growth factor I, GH, prolactin, cortisol and the thyroid hormones). On day 11 of the dietary treatment, LH pulse frequency and mean FSH concentrations in Group M + L had increased relative to Group M and to day 0. Plasma concentrations of prolactin and insulin on days 3 and 10, and glucose and insulin-like growth factor I on day 10, were higher in Group M + L than in Group M, but only cerebrospinal fluid concentrations of insulin, glucose and certain amino acids were affected by the dietary treatments on days 3 and 10. Cerebrospinal fluid, but not plasma, concentrations of aspartate, tyrosine, cystine, phenylalanine and arginine on day 3, and glutamine, gamma-aminobutyric acid, threonine, alanine on days 3 and 10, were higher in Group M + L relative to Group M. On day 10, plasma and cerebrospinal fluid concentrations of arginine, phenylalaine, proline, tyrosine, methionine and phosphoserine, but only the plasma concentrations of linoleic acid, aspartate and serine, were higher in Group M + L than in Group M. Concentrations of triiodothyronine, thyroxine, and cortisol in plasma and cerebrospinal fluid were not affected. These results show that the nutritional stimulation of gonadotrophin secretion is accompanied primarily by fluctuations in plasma and cerebrospinal fluid concentrations of insulin and certain amino acids, which suggests that, when nutritional status is improved, insulin, amino acids and possibly glucose interact to modulate GnRH secretion.
authors.affiliation: Faculty of Agriculture (Animal Science), University of Western Australia, Nedlands, Australia.
authors.forename: D W
authors.initials: DW
authors.lastname: Miller
authors.forename: D
authors.initials: D
authors.lastname: Blache
authors.forename: R
authors.initials: R
authors.lastname: Boukhliq
authors.forename: J D
authors.initials: JD
authors.lastname: Curlewis
authors.forename: G B
authors.initials: GB
authors.lastname: Martin
mesh_terms: D000596:Amino Acids / Q000097:blood / Q000134:cerebrospinal fluid; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D005230:Fatty Acids, Nonesterified / Q000097:blood / Q000134:cerebrospinal fluid; D005640:Follicle Stimulating Hormone / Q000097:blood / Q000378:metabolism; D005947:Glucose / Q000134:cerebrospinal fluid; D006065:Gonadotropins, Pituitary / Q000378:metabolism*; D013006:Growth Hormone / Q000097:blood / Q000134:cerebrospinal fluid; D006854:Hydrocortisone / Q000097:blood / Q000134:cerebrospinal fluid; D007328:Insulin / Q000097:blood / Q000134:cerebrospinal fluid; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000134:cerebrospinal fluid; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism; D008297:Male; D011388:Prolactin / Q000097:blood / Q000134:cerebrospinal fluid; D011863:Radioimmunoassay; D012756:Sheep / Q000502:physiology*; D013963:Thyroid Hormones / Q000097:blood / Q000134:cerebrospinal fluid; D013997:Time Factors
chemical_list: D000596:Amino Acids; D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D006065:Gonadotropins, Pituitary; D007328:Insulin; D013963:Thyroid Hormones; D007334:Insulin-Like Growth Factor I; D011388:Prolactin; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D013006:Growth Hormone; D005947:Glucose; D006854:Hydrocortisone