Pharmacological doses of GH are known to impair glucose tolerance. In the present study we have employed the euglycemic insulin and hyperglycemic clamp techniques to examine the effect of physiological elevations in plasma GH concentrations (27 ± 2 ng/ml) on the tissue responses to insulin and on glucose-stimulated insulin secretion. Three types of studies (low dose insulin clamp, high dose insulin clamp, and hyperglycemic clamp) were performed in young healthy volunteers before and after the infusion of GH (2 /ig/kg-h) for 2 and 12 h. In the low dose insulin clamp studies, the plasma insulin concentration was acutely raised and was maintained at 59 ± 4 juU/ml, while plasma glucose was maintained at basal levels. After 2 h of GH infusion, insulin-mediated glucose metabolism was slightly, although not significantly, decreased (4.48 ± 0.56 vs. 5.04 ± 0.39 mg/kg-min) in the control study. After 12 h of GH infusion, however, insulin-mediated glucose uptake decreased by 32 ± 9% (3.36 ± 0.40 mg/kg-min; P < 0.01). Basal endogenous glucose production (2.02 ± 0.07 mg/kg-min) was suppressed by 89 ± 4% in the control study. After short term GH infusion, the degree of suppression (90 ± 5%) was similar to the control value. After 12 h of GH infusion, however, suppression of endogenous glucose production (78 ± 5%) was slightly less than that in controls (P < 0.05). In the high dose insulin clamp studies, GH was infused for either 2 or 12 h, after which plasma insulin levels were increased to 2292 ± 96 /xU/ml while maintaining euglycemia (high dose insulin clamp study). Insulin-mediated glucose uptake was 11.22 ± 0.53 mg/kg-min in the control study, slightly lower during short term GH infusion (9.56 ± 1.00 mg/kg-min) and significantly diminished after long term GH infusion (7.16 ± 1.12 mg/kg-min; P < 0.02). In the hyperglycemic clamp studies, plasma glucose was raised and maintained at 125 mg/dl above the basal level. Glucose metabolism in controls (8.68 ± 0.53 mg/ kg-min) was decreased by 31 ± 7% after 2 h and by 44 ± 6% after 12 h of GH infusion. The mean increment in plasma insulin in response to hyperglycemia (control, 56 ± 10 juU/ml) was unaltered after 2 and 12 h of GH administration. Total binding of [ 125 I]insulin to monocytes was 7.0 ± 0.5% before GH infusion. After 2 h of GH administration, no change in total specific insulin binding (7.4 ± 0.4%) occurred. After 12 h of exposure to GH, however, total binding was decreased (5.9 ± 0.4%; P < 0.02) due to a decrease in receptor affinity.We conclude that physiological elevations in GH 1) induce a state of insulin resistance within 2-12 h, 2) only slightly impair insulin's suppressive effect on endogenous glucose production, indicating that the primary site of insulin resistance resides in peripheral tissues, 3) do not alter the plasma insulin response to hyperglycemia, and 4) cause a decrease in insulin binding that results from a decrease in receptor affinity. The inability to overcome the defect in glucose metabolism at high plasma insulin concentrations suggests that a...

Diabetic ketoacidosis is associated with an excess secretion of counterregulatory hormones. The effect of rehydration on these endocrine derangements before insulin administration is unknown. Therefore, we measured the effect of rehydration with hypoosmolal fluid (220 mosmol/kg) on blood glucose (BG), immunoreactive insulin (IRI), immunoreactive C-peptide (IRCP), immunoreactive glucagon (IRG), human pancreatic polypeptide (hPP), growth hormone (GH), prolactin (PRL), cortisol, aldosterone, renin (PRC), epinephrine, norepinepnrine, and parathyroid hormone (PTH) in ketoacidotic diabetic patients [pH 7.03 ± 0.05 (SEM); n = 8] and in patients (n = 2) with nonketotic hyperglycemia (BG, 29.8 mmol/L and 46.8 mmol/L). The cumulative net fluid balance after rehydration was 4364 ± 690 ml. Basal insulin was inappropriately low, and IRCP was below the normal range (1.5 ± 0.5 ng/ml). Serum osmolality fell during hypoosmolal rehydration (n = 9) from 335 ± 11 to 315 ± 9 mosmol/kg. Rehydration with hypoosmolal fluid with bicarbonate added at a pH of less than 7.2 induced a fall in BG ranging from 6.1 mmol/L to 22.6 mmol/L, or of 16.7% to 79.8% of the initial BG level, as well as a decrease in plasma lactate and urinary glucose. These effects were paralleled by a decrease in IRG, cortisol, epinephrine, norepinephrine, aldosterone, and PRC. No fall in BG was seen in one patient whose dehydrated state was maintained by infusion of isotonic saline. Low dose insulin treatment was initiated in all patients immediately when no further fall in blood glucose levels was achieved. We conclude that rehydration improves the metabolic situation in severe diabetic hyperglycemia and ketoacidosis by reducing (a) the availability of counterregulatory hormones and (b) peripheral insulin resistance on a cellular level. Thus, proper rehydration will support the beneficial action of simultaneous low dose insulin treatment in patients with severe hyperglycemia.

Insulin production rate has been estimated in healthy male volunteers (n = 16), and evaluated with respect to splanchnic glucose exchange. Insulin production rate was calculated from splanchnic immunoreactive C-peptide output. C-peptide secretion was estimated by the hepatic venous catheter technique both in the basal state and for 2 h following ingestion of various glucose loads (0, 12.5, 25, 50, 75, and 100 g). The results demonstrate a basal insulin production rate of 0.017 +/- 0.002 U/min (mean +/- SEM) or 2.04 U/2 h. Values rose in a dose dependent manner from 2.6 +/- 1.1 U/2 h after ingestion of 12.5 g of glucose to 10.8 +/- 1.1 U/2 h following a glucose load of 100 g. Insulin retention by the liver was estimated at 0.012 +/- 0.001 U/min in the basal state, and ranged from 47-85% (70 +/- 2%) of production following an oral glucose load. It was also demonstrated 1) that the relative splanchnic glucose output was inversely related to the amount of ingested glucose, and reached a minimum when glucose in excess of 50 g was ingested; and 2) that hepatic glucose retention was directly proportional to insulin production rate (r = 0.83; p less than 0.001; n = 15). It is suggested that the adaptive capacity of the splanchnic bed to retain glucose depending on the amount of ingested glucose guarantees that splanchnic glucose output fluctuates in healthy man only within a narrow range.

To elucidate the potency of continuous vs. intermittent exposure to hormonal stimuli, hepatic glucose production of isolated perfused rat livers was monitored in response to glucagon and insulin infusion. Using a nonrecirculating perfusion system, continuous exposure to glucagon (35 pM) induced a rise in hepatic glucose production from basal 0.33 +/- 0.03 mmol/(96 min X 100 g BW) to 0.65 +/- 0.02 mmol/(96 min X 100 g BW), while intermittent exposure (3 min on/off intervals; total dose 50%) to the same glucagon concentration elicited an almost identical rise in hepatic glucose production to 0.59 +/- 0.12 mmol/(96 in X 100 g BW). Insulin (100 mU/liter) given continuously and intermittently (3 min on/off intervals) inhibited glucagon-stimulated (70 pM) hepatic glucose production to the same extent, i.e. by 37.4% and 41.1%, respectively. Doubling the off period to 6 min and thereby reducing the total hormone dose to 33% did not diminish insulin's suppressive effect on glucagon-stimulated hepatic glucose release (34.6%). When the latter infusion protocol was applied with insulin at 300 mU/liter, hepatic glucose production during the first 40 min of glucagon infusion was more restrained (P less than 0.01) than during continuous delivery of 100 mU/liter, although the same amount of insulin was infused per period of time. In parallel, glucagon-stimulated cAMP release was similarly suppressed by insulin in all experiments. From this we conclude that the effect on hepatic glucose production of pulsatile administration of glucagon as well as of insulin, depending on the applied time interval of hormone exposure, is equipotent or even superior to the respective hormones' continuous infusion even if the hormone load is significantly reduced.

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