Gamma-butyrobetaine does not restore beta-hydroxybutyrate inhibition of hepatic ketogenesis in diabetic, untreated ewes

A possible insulin-independent regulatory mechanism of hepatic ketogenesis was studied in eight experiments on five ewes surgically catheterized in hepatic, portal, and mesenteric veins, and femoral artery and femoral vein. Ewes were made diabetic with alloxan (50 mg/kg bw, iv) . Euglycemia was maintained with daily insulin injections (Iletin-100 ~35 lU/d) until three days prior to each experiment, when injections were withheld to induce ketosis. Ewes were housed in 1.8 X 3.0 m indoor pens under natural lighting in a thermoneutral environment. Experiments consisted of three infusion periods: (1) para-aminohippurate (1.5% @ 0.764 ml/min) infusion into the common mesenteric vein (control); (2) para-aminohippurate as in (1) and beta-hydroxybutyrate (1.18 mmol/min) into the common mesenteric vein; and (3) paraaminohippurate and beta-hydroxybutyrate as in (2) and gamma-butyrobetaine (1.18 mmol/min) into the common mesenteric vein. For each period, each infusate was allowed to equilibrate for one hour and then three blood samples were taken simultaneously from the hepatic, portal, and femoral veins and femoral artery at thirty minute intervals and analyzed for beta-hydroxybutyrate, acetoacetate, non-esterified fatty acids, glucose, and para-aminohippurate. Blood flows were calculated by measuring downstream dilution of para-aminohippurate and net fluxes were calculated by multiplying tissue veno-arterial concentrations by tissue blood flow. Blood glucose (~10 mM) was unaffected by infusion. Beta-hydroxybutyrate decreased hepatic flow (3.6 to 2.5 L/min, P<.01), but did not change portal flow. Consequently, portal flow contribution to the liver increased from 73 to 83% (P<.01) during beta-hydroxybutyrate infusion. Relative to control, beta-hydroxybutyrate infusion decreased (P<.01) non-esterified fatty acid arterial concentrations (2.1 to 1.1 mM) and hepatic (0.7 to 0.2 mmol/min) and total splanchnic (0.6 to 0.2 mmol/min) net uptakes. Beta-hydroxybutyrate infusion increased acetoacetate arterial concentrations (1.2 to 1.5 mM, P<.05) and decreased (P<.05) hepatic release (0.5 to 0.1 mmol/min)(i.e., decreased ketogenesis) and total splanchnic release (0.6 to 0.1 mmol/min). Similar to its effects on acetoacetate, beta-hydroxybutyrate infusion increased beta-hydroxybutyrate arterial concentrations (7.6 to 12.3 mM, P<.01) but decreased net hepatic release (1.6 to 0.7 mmol/min, P<.01) and total splanchnic release (2.1 to 1.3 mmol/min, P<.1). Gamma-butyrobetaine infusion did not reverse any beta-hydroxybutyrate effects. According to this data beta-hydroxybutyrate may regulate ketogenesis by decreasing hepatic non-esterified fatty acid uptake and subsequent conversion to acetoacetate and beta-hydroxybutyrate. Gamma-butyrobetaine, in contrast, had no effect on hepatic ketogenesis nor nonesterified fatty acid uptake, suggesting that beta-hydroxybutyrate inhibition was not at the carnitine acyltransferase level or that gamma-butyrobetaine may not be extracted by the liver in quantities sufficient to counteract observed effects of beta-hydroxybutyrate.