As bstract. The effect of ketone bodies on glucose production (Ra) and utilization (Rd) was investigated in the 24-h starved, conscious unrestrained miniature pig. Infusing Na-DL-3-OH-butyrate (Na-DL-f-OHB) and thus shifting the blood pH from 7.40 to 7.56 resulted in a decrease of Ra by 52% and of Rd by 45%, as determined by the isotope dilution technique. Simultaneously, the concentrations of arterial insulin and glucagon were slightly enhanced, whereas the plasma levels of glucose, lactate, pyruvate, alanine, a-amino-N, and free fatty acids (FFA) were all reduced. Infusion ofNa-bicarbonate, which yielded a similar shift in blood pH, did not mimick these effects. Infusion of equimolar amounts of the ketoacid, yielding a blood pH of 7.35, induced similar metabolic alterations with respect to plasma glucose, Ra, Rd, and insulin; however, plasma alanine and a-amino-N increased.Infusing different amounts of Na-DL-3-OHB resulting in plasma steady state levels of ketones from 0.25 to 1.5 mM had similar effects on arterial insulin and glucose kinetics. No dose dependency was observed.Prevention of the Na-DL-3-OHB-induced hypoalaninemia by simultaneous infusion of alanine (1 ttmol/kg X min) did not prevent hypoglycemia.Infusion of Na-DL-l-OHB plus insulin (0.4 mU/kg in plasma glucose and Ra; however, on infusion of somatostatin plus Na-DL-3-OHB, hypoglycemia and the reduced Ra were maintained.In the anaesthetized 24-h starved miniature pig, Na-DL-3-OHB infusion decreased the hepatic exchange for glucose, lactate, and FFA, whereas the exchange for glycerol, alanine, and a-amino-N as well as liver perfusion rate were unaffected. Simultaneously, portal glucagon and insulin as well as hepatic insulin extraction rate were elevated. Leg exchange for glucose, lactate, glycerol, alanine, a-amino-N, and FFA were decreased, while ketone body utilization increased.Repeated infusion of Na-DL-3-OHB at the fourth, fifth, and sixth day of starvation in the conscious, unrestrained mini-pig resulted in a significant drop in urinary nitrogen (N)-excretion. However, this effect was mimicked by infusing equimolar amounts of Na-bicarbonate. In contrast, when only the ketoacid was given, urinary Nexcretion accelerated.To summarize: (a) Ketone bodies decrease endogenous glucose production via an insulin-dependent mechanism; in addition, ketones probably exert a direct inhibitory action on gluconeogenesis. The ketone bodyinduced hypoalaninemia does not contribute to this effect. (b) The counterregulatory response to hypoglycemia is reduced by ketones. (c) As a consequence of the decrease in Ra, glucose utilization declines during ketone infusion.(d) The insulin-stimulated MCR for glucose is not affected by ketones. (e) Ketones in their physiological moiety do not show a protein-sparing effect.

The rate of glucose production was estimated in the conscious, unrestrained miniature pig during metabolic adaptation to starvation (up to 120 h) by the simultaneous use of three different techniques: 1) the isotopedilution technique, 2) the arteriohepatovenous catheter technique, and 3) the urinary nitrogen balance. During the experimental period 1) whole-body glucose turnover decreased, whereas the amount of glucose recycling increased; 2) splanchnic glucose output decreased, whereas the rate of splanchnic precursor extraction increased up to 48 h, followed by a decrease; 3) gut glucose consumption amounted to about 30% of splanchnic glucose output; and 4) urinary nitrogen excretion declined continuously. The comparison of the different methods revealed that during starvation 1) tracer-determined glucose production rate was within the range (+/- 10%) of the splanchnic glucose output; 2) mean hepatic glucose output overestimated the tracer data by about 30-40%; 3) splanchnic glucose output underestimated hepatic glucose production by the amount of gut glucose consumption; 4) tracer-determined glucose recycling corrected for isotope dilution and amino acid contribution was within the range of splanchnic gluconeogenic precursor extractions. Considering the limitations (e.g., gut glucose consumption, gut lactate and alanine release, blood flow measurement) and methodological problems of the different approaches applied, it is evident that each method reflects different events. It is suggested that the versatile tracer technique combined with nitrogen balance should be preferred for measurement of endogenous glucose production.

The effect of different thyroid states on glucose homeostasis was investigated during metabolic adaptation to starvation in the conscious unrestrained miniature pig. Moderate hyperthyroidism increased the rate of glucose turnover, whereas hypothyroidism was without effect. Glucose recycling was elevated in hyperthyroid pigs, and reduced after thyroidectomy. Supplementary doses of T4 normalized total glucose recycling. Glucose metabolic clearance rate and pool size were unaffected by thyroid hormones. During starvation serum insulin showed a similar decrease in all thyroid states; glucagon increased in euthyroid and hypothyroid pigs, although it was already elevated in the hyperthyroid fed state. Serum cortisol levels although varying were enhanced in hyperthyroid and hypothyroid-T4-treated pigs. Glucogenic precursor concentration and cumulative urinary N-excretion were increased in hyperthyroid pigs. It is concluded that 1) even a moderate hyperthyroidism produces an increase in glucose turnover and a concomitant acceleration in protein breakdown, and 2) thyroid hormone is essential for the starvation-induced total glucose recycling.

The effects of short-term starvation (up to 5 days) on hepatic ketone body production was investigated in the conscious unrestrained miniature pig in vivo. Starvation induced an increase in arterial free fatty acid concentration (0.2-0.7 mM) with a concomitant elevation in hepatic free fatty acid extraction [-1.4-5.7 mumol/kg. minute),r = 0.53, P less than 0.005]. Ketone body production (sum of acetoacetate + beta-hydroxybutyrate) increased from 1.5 to 5.8 mumol/(kg . minute) in parallel (r = 0.71, P less than 0.0005). During starvation arterial insulin levels decreased, glucagon increased, cortisol remained unchanged and a "low T3 state' was observed. These data differ in some aspects from those reported for humans and dogs. Thus a species-specific variation in the fuel economy of the pig's body is proposed.