Metabolic adaptations associated with irreversible glucose loss are different to those observed during under-nutrition.
In this study the hypothesis that irreversible glucose loss results in an 'uncoupling' of the somatotrophic axis (increasing plasma GH levels and decreasing plasma IGF-I) was tested. During periods of negative energy balance the somatotrophic axis respond by increasing plasma GH and decreasing plasma IGF-I levels. In turn, elevated GH repartitions nutrient by increasing lipolysis and protein synthesis, and decreases protein degradation. Irreversible glucose loss was induced using sub-cutaneous injections of phloridizin. Seven non-lactating cows were treated with 8g/day phloridizin (PHZ) and seven control animals (CTRL, 0g/day), while being restricted to a diet of 80% maintenance. PHZ treatment increased urinary glucose excretion (P<0.001), resulting in hypoglycemia (P<0.001). As a response to this glucose loss, the PHZ treated animals had elevated plasma NEFA (P<0.005) and BHBA (P<0.001) levels. Average plasma insulin concentrations were not altered with PHZ treatment (P=0.059). Plasma GH was not different between the two groups (P>0.1), whereas plasma IGF-I levels decreased significantly (P<0.001) with PHZ treatment. The decline in plasma IGF-I concentrations was mirrored by a decrease in the abundance of hepatic IGF-I mRNA (P=0.005), in addition the abundance of hepatic mRNA for both growth hormone receptors (GHR(tot) and GHR(1A)) was also decreased (P<0.05). Therefore, the irreversible glucose loss resulted in a partial 'uncoupling' of the somatotrophic axis, as no increase in plasma GH levels occurred although plasma IGF-I levels, hepatic IGF-I mRNA declined, and the abundance of liver GH receptor mRNA declined.
Meier
S
S
Dexcel Limited, Private Bag 3221, Hamilton, New Zealand. Susanne.meier@dexcel.co.nz
Gore
P J S
PJ
Barnett
C M E
CM
Cursons
R T
RT
Phipps
D E
DE
Watkins
K A
KA
Verkerk
G A
GA
D020155:3-Hydroxybutyric Acid / Q000097:blood; D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000378:metabolism*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D005947:Glucose / Q000378:metabolism*; D006029:Glycosuria / Q000662:veterinary; D013006:Growth Hormone / Q000097:blood; D007003:Hypoglycemia / Q000662:veterinary; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000235:genetics; D008066:Lipolysis / Q000502:physiology; D008099:Liver / Q000737:chemistry; D044342:Malnutrition / Q000378:metabolism / Q000662:veterinary*; D010695:Phlorhizin / Q000008:administration & dosage; D014176:Protein Biosynthesis / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis
D005230:Fatty Acids, Nonesterified; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D010695:Phlorhizin; D005947:Glucose; D020155:3-Hydroxybutyric Acid