The physiological impact of the contemporary shift from regular meal consumption to grazing/snacking behaviour^1,2, remains poorly understood.  We have reported previously that feeding male rodents three meals/night enhances growth hormone (GH) rhythmicity and skeletal growth by activating the GH secretagogue receptor (GHSR)³, whereas grazing elevates fat mass.  Similar endocrine responses occur in men receiving patterned nasogastric enteral feed³.  Here we examine the impact of these feeding patterns and the role of GHSR in female mice.

5 week-old female wild-type (WT) and loxTB-GHSR (GHSR-null) littermate mice, were fed either ad libitum (AL), grazing (1/24^th daily AL consumption every 30 mins in the dark phase), or in meals (3x1hr periods of AL feeding at the start, middle and end of the dark phase) for 3 weeks (n=9-12 per group) (Animal procedures were performed in accordance with the Animals (Scientific Procedures) Act, 1986 (UK), the Cardiff University Animal Welfare Ethical Review Body (AWERB) and reported as per the ARRIVE guidelines).  Mice were anaesthetized with Dolethal (200mg/kg; i.p.) nose-anus length measured and decapitated.  Femora and tibiae were dissected and the length measured with a hand-held micrometer, tibial epiphyseal plate width (EPW) being determined by light microscopy.  A range of tissues were dissected and weighed.  All data reported are mean ± SEM, with statistical comparisons performed by 1-way ANOVA with Bonferroni’s multiple comparison post hoc test.

Cumulative food intake (cF/I), overall weight gain and indices of longitudinal growth were unaffected by either feeding pattern in WT females.  However, meal-fed GHSR-null mice showed a 12% reduction in cF/I (P=0.0002 vs AL-fed GHSR-null mice), a 60% reduction in weight gain (P=0.0099 vs AL-fed GHSR-null mice) and a 2.5% reduction in femoral length (P=0.0192).  Tibial EPW, an accurate marker of growth rate, was reduced by 18% in both grazing and meal-fed WT females (P=0.0158; P=0.0029 vs AL-fed WT female), this effect being less pronounced in GHSR-null females.  Liver, kidney, pituitary and ovarian weights were unaffected by these feeding patterns in either WT or GHSR-null mice, adrenal weight being reduced by 19% in meal-fed GHSR-null females (P=0.0309 vs AL-fed GHSR-null mice).  Although inguinal and omental white adipose tissue (WAT) weights were unaffected by grazing or meal-feeding in WT mice, grazing elevated proportionate retroperitoneal WAT weight in WT females by 32% (P=0.0219 vs AL-fed WT mice), mean proportionate interscapular brown AT weight in grazing WT females being 121% of that in AL-fed mice (P=0.0724).  These effects were abolished in GHSR-null mice.

Unlike in males, meal-feeding failed to accelerate skeletal growth in female mice, but activation of the ghrelin-GHSR axis is essential for maintaining food intake and body weight in meal-fed females.  In contrast, grazing-enhanced lipid storage in WT female mice is more widespread in males and dependent upon GHSR activation in both sexes.  Thus, while feeding patterns appear to modulate the ghrelin system similarly in males and females, the enhancement of GH pulsatility is male-specific.  Thus, the contemporary shift from regular meal consumption to grazing/snacking behaviour may be detrimental to growth and metabolic outcomes, particularly in males.