Endocrine Abstracts

Patterns of food consumption have a profound influence on hormone rhythmicity and fat storage, but until now only crude manipulations of food availability have been possible in rodents. We have used a CLAMS-based system in conjunction with automated serial blood sampling to investigate the effect of continuous feeding on ghrelin secretion and adiposity. Six-week old male Sprague–Dawley rats (n=6) were housed in metabolic cages and ad-libitum fed with standard chow for 3 weeks (12 h light:12 h darkness; lights on at 0600 h). A cohort of age- and weight-matched rats (n=4) were housed in CLAMS cages in the same room and subjected to paired, continuous nocturnal feeding (1/24th of the total daily food intake of ad-libitum-fed rats being available every 30 min of the 12 h dark phase) for 3 weeks. During week 3 jugular vein catheters were introduced under isofluorane anaesthesia and automated hourly blood sampling initiated after 48 h recovery. Continuously fed rats consumed only 86% of their total daily allowance (P<0.01), but body weight (BW) was not significantly reduced. The feeding-associated suppression of circulating octanoylated ghrelin in the early dark phase was significantly delayed in continuously fed rats: plasma concentrations at 1800, 1900 and 2400 h being 4.1-, 2.7- and 3.3-fold that in ad-libitum-fed rats. Although nose-anus length and pituitary weight were unaffected by continuous feeding, femoral length was reduced by 2% (P<0.05) and proportionate liver weight increased by 6% (P<0.05). Proportionate abdominal fat pad weights were not significantly affected by continuous feeding, but when corrected for cumulative food intake, the retroperitoneal depot (which is most sensitive to ghrelin exposure) showed elevated lipid storage efficiency (increased by 24%; P<0.05). Thus, continuous feeding fails to induce the post-prandial suppression of ghrelin secretion and predisposes rats to increased fat accumulation, suggesting that longer-term grazing may be obesogenic without increasing caloric intake.