Figure 1.
Body temperature (Tb) changes over the annual cycle of the 13-lined ground squirrel.
The Tb trace during hibernation was obtained with a telemeter implanted in a squirrel housed in an environmental chamber maintained at 3–4°C. Tb lines in spring and summer are hand-drawn for illustration. Winter torpor bouts last from a few days to 2–3 wk, and interbout arousals (IBA) to normothermia typically last <24 h. ET, early torpor; LT, late torpor.
Figure 2.
Plasma and lipoprotein cholesterol concentrations over the annual cycle.
Plasma total, esterified, and free cholesterol (A–C) in fasted and fed spring (SPR) (open bars) and summer (SUM) (grey bars) squirrels, and in hibernators (filled bars) during late torpor (LT), and interbout arousal (IBA) are shown. Total, esterified, and free cholesterol of fast protein liquid chromatography fractionated lipoproteins from a separate set of squirrels are shown (D–F). Plasma cholesterol (G) and body mass (H) of a third set of fed squirrels at 6, 4, and 2 wk prior to hibernation, on the day they entered the cold room (indicated with arrow), and at 4, 8 and 12 wk of hibernation are also shown. Groups with the same letter are not different. All values represent means ± s.e.m., n = 5 or 6.
Table 1.
Whole body and tissue cholesterol levels in ground squirrels.
Figure 3.
Tissue cholesterol levels in ground squirrels.
Liver, white adipose tissue (WAT), and intestinal mucosa cholesteryl ester (CE) (A–C) and free cholesterol (FC) (D–E) levels in fasted spring (SPR) (open bars) and summer (SUM) (grey bars) squirrels, and in hibernators (filled bars) in entrance (EN), late torpor (LT), and interbout arousal (IBA) are shown. Groups with the same letter are not different. All values represent means ± s.e.m., n = 5 or 6 for all groups.
Figure 4.
HMG-CoA reductase (HMGR) intestinal mRNA expression and Cholesterol 7 alpha-hydroxylase (CYP7A1) liver protein expression.
Gene and protein expression in fasted summer (SUM) (grey bars) squirrels and hibernators (filled bars) in entrance (EN), early torpor (ET), late torpor (LT), arousal (AR), and interbout arousal (IBA) are shown. HMGR gene expression is normalized to reference genes (acidic ribosomal phosphoprotein, succinate dehydrogenase complex subunit A, and hypoxanthine-guanine phosphoribosyltransferase) and expressed relative to SUM which was set at 1.0. CYP7A1 expression is normalized to β-actin protein expression (example blot panel C). Groups with the same letter are not different. All values represent means ± s.e.m. and n = 5 or 6.
Table 2.
Biliary lipid composition in summer and late torpor ground squirrels.
Figure 5.
Plasma, lipoprotein, and tissue triglycerides (TG) and free fatty acids (FFA) over the annual hibernation cycle.
(A) Total plasma and (B) lipoprotein TGs following fractionation by FPLC in fasted and fed spring (SPR) (open bars) and summer (SUM) (grey bars) squirrels, and in hibernators (filled bars) during late torpor (LT), and interbout arousal (IBA) squirrels are shown. Tissue TG (C, D, E) and FFA levels (F, G, H) in liver, white adipose tissue (WAT) and intestinal mucosa in fasted SPR, SUM, entrance (EN), LT and IBA squirrels are shown. Groups with the same letter are not different. All values represent means ± s.e.m., n = 5–7.
Figure 6.
Plasma β-hydroxybutyrate (BHB) concentration over the annual hibernation cycle.
BHB concentrations in fasted and fed spring (SPR) (open bars) and summer (SUM) (grey bars) squirrels, and in hibernators (filled bars) during early torpor (ET), late torpor (LT),arousing (AR), and interbout arousal (IBA) squirrels are shown. Groups with the same letter are not different. All values represent means ± s.e.m., n = 5 or 6 for all groups.
Figure 7.
Schema of the metabolic profile of the 13-lined ground squirrel over the annual hibernation cycle.
Abbreviations: TG, triglyceride, ApoA-I, apolipoproteinA-I, LT, late torpor, ET, early torpor, IBA, interbout arousal, CYP7A1, cholesterol 7 alpha-hydroxylase; BHB, β-hydroxybutyrate.