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C L Adam, P A Findlay, C E Kyle, P Young and J G Mercer

Abstract

Castrate male sheep (wethers, average liveweight 38 ± 0·6 kg) were given one of the following diets for 10 weeks followed by euthanasia (n=8/group): high-energy high-protein providing 1·5 times the energy required to maintain liveweight (maintenance) (group 1·5M), low-energy low-protein at 0·5 maintenance (0·5M), or low-energy high-protein at 0·5 maintenance (0·5M+P). 1·5M wethers gained 22% liveweight whereas 0·5M and 0·5M+P wethers lost 18 and 13% liveweight respectively. Relative to the 1·5M group, the 0·5M and 0·5M+P groups had similar plasma concentrations of glucose and cortisol throughout, but elevated non-esterified fatty acids (P<0·001) and reduced IGF-I and insulin (P<0·05, 0·01 or 0·001) from 1 week onwards. Each week blood samples were taken every 12 min for 4 h and plasma assayed for LH. Mean concentration over 4 h, LH pulse frequency and LH pulse amplitude showed no progressive change in 1·5M sheep. However, in both 0·5M and 0·5M+P groups mean LH increased (P<0·001 and P<0·01 respectively), pulse frequency decreased (P<0·01 and P<0·01) and pulse amplitude increased (P<0·001 and P<0·01) over the 10-week period. Anterior pituitary LH content was greater in 0·5M (P<0·01) and 0·5M+P (P<0·05) than in 1·5M sheep. Coronal sections (20 μm) of hypothalamic brain tissue were subjected to in situ hybridisation to determine gene expression for neuropeptide Y (NPY). NPY mRNA was concentrated in the arcuate nucleus and median eminence, with total amounts greater in both 0·5M (310%, P<0·001) and 0·5M+P (333%, P<0·01) groups than in 1·5M sheep (100%). These data reveal that chronic low dietary energy intake by long-term castrates, with high or low protein intake, reduces LH pulse frequency but increases the circulating levels of LH by virtue of an increase in pulse amplitude, and concomitantly increases hypothalamic NPY gene expression.

Journal of Endocrinology (1997) 152, 329–337

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Z A Archer, S M Rhind, P A Findlay, C E Kyle, M C Barber and C L Adam

Nutritional feedback provided by systemic hormones, such as insulin and leptin, influences reproductive neuroendocrine output within the hypothalamus, yet the mechanisms and their interaction with photoperiodic cues remain unresolved in seasonal species. Here, peripheral glucose (G) infusion was used to increase endogenous concentrations of insulin and leptin in food-restricted sheep kept in either long-day (LD) or short-day (SD) photoperiod, and responses were examined in terms of pulsatile luteinising hormone (LH) (gonadotrophin-releasing hormone by inference) output and hypothalamic gene expression for nutritionally sensitive neuropeptides and receptors. We addressed the hypothesis that these hypothalamic responses were correlated and influenced by photoperiod. Oestradiol-implanted, castrated male sheep were kept 16 weeks in SD (8 h light/day) or LD (16 h light/day) and then transferred to the opposite photoperiods for 8 weeks, during which food was restricted to 90% requirement to maintain body weight (maintenance). For the final 6 days, food was reduced to 75% maintenance, and sheep in both photoperiods were infused intravenously with G (60 mM/h) or saline (S) (n=8/group). G-infused sheep had higher mean plasma concentrations of G, insulin and leptin than S-infused sheep, with no effect of photoperiod. In LD, but not in SD, G infusion increased LH pulse frequency and pulse amplitude. In LD, but not in SD, gene expression in the hypothalamic arcuate nucleus was lower in G- than S-infused sheep for neuropeptide Y (NPY) and agouti-related peptide (AGRP) and was higher in G- than S-infused sheep for pro-opiomelanocortin (POMC). Gene expression for leptin and insulin receptors was not affected by photoperiod or infusion. These results are consistent with the involvement of NPY, AGRP and POMC in mediating the reproductive neuroendocrine response to increased systemic nutritional feedback, and they support the hypothesis that hypothalamic responses to nutritional feedback are influenced by photoperiod in sheep.

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M A Hyatt, G S Gopalakrishnan, J Bispham, S Gentili, I C McMillen, S M Rhind, M T Rae, C E Kyle, A N Brooks, C Jones, H Budge, D Walker, T Stephenson and M E Symonds

The liver is a major metabolic and endocrine organ of critical importance in the regulation of growth and metabolism. Its function is determined by a complex interaction of nutritionally regulated counter-regulatory hormones. The extent to which hepatic endocrine sensitivity can be programed in utero and whether the resultant adaptations persist into adulthood is unknown and was therefore the subject of this study. Young adult male sheep born to mothers that were fed either a control diet (i.e.100% of total live weight-maintenance requirements) throughout gestation or 50% of that intake (i.e. nutrient restricted (NR)) from 0 to 95 days gestation and thereafter 100% of requirements (taking into account increasing fetal mass) were entered into the study. All mothers gave birth normally at term, the singleton offspring were weaned at 16 weeks, and then reared at pasture until 3 years of age when their livers were sampled. NR offspring were of similar birth and body weights at 3 years of age when they had disproportionately smaller livers than controls. The abundance of mRNA for GH, prolactin, and IGF-II receptors, plus hepatocyte growth factor and suppressor of cytokine signaling-3 were all lower in livers of NR offspring. In contrast, the abundance of the mitochondrial protein voltage-dependent anion channel and the pro-apoptotic factor Bax were up regulated relative to controls. In conclusion, maternal nutrient restriction in early gestation results in adult offspring with smaller livers. This may be mediated by alterations in both hepatic mitogenic and apoptotic factors.