A stimulatory effect of FFA on glycolysis unmasked in cells with impaired oxidative capacity

The physiological importance of the glucose fatty acid cycle has been controversial. Many studies have failed to demonstrate an inhibitory effect of free fatty acids (FFA) on glucose utilization. Using both hepatoma cells (Hep G2) and human erythrocytes, which have poor oxidative capacity and metabolize glucose primarily anaerobically, we have demonstrated a unique stimulatory effect of FFA on glycolysis. Fructose 2,6-bisphosphate (F-2,6-P2) concentrations also increased significantly in Hep G2 cells incubated with palmitic acid. In contrast, F-2,6-P2 concentrations fell in primary cultured hepatocytes incubated with palmitic acid in association with increased oxidation of FFA and accumulation of beta-hydroxybutyrate. We propose that a stimulatory effect of FFA on glycolysis reported here for the first time may have been masked in previous studies performed in tissues in which the oxidation of FFA and the accumulation of intermediates such as citrate may have decreased F-2,6-P2 concentrations. We conclude that the spectrum of FFA effects in glycolysis probably depends on tissue oxidative capacity.

Lack of effect of dehydroepiandrosterone in obese men

To assess the effects of dehydroepiandrosterone (DHEA) on weight and body fat mass in young obese men, six obese (body mass index, 31.5 +/- 2.9 (s.e.] men were studied at baseline, after 28 days of placebo administration, and again after 28 days of DHEA (1600 mg/day) administration. Body fat mass was assessed on each occasion by three separate methods: hydrostatic weighing, impedance plethysmography, and skinfold measurements at four body sites. Waist-to-hip ratios were recorded. In addition, tissue sensitivity to insulin was determined using the modified minimal model technique, and serum lipids were assayed. Serum DHEA-sulfate levels rose from 7.4 +/- 1.7 mumol/l at baseline to 39.8 +/- 11.9 mumol/l after DHEA administration (P less than 0.05). Although body fat mass was reduced in two of the six men following DHEA administration, for the group as a whole neither total body weight, body fat mass, or waist-to-hip ratio changed significantly during the study. No change in either tissue insulin sensitivity or serum lipids was observed. These observations suggest that, at a daily dose of 13.4-19.7 mg/kg, short-term DHEA administration does not affect the total weight, body fat mass, fat distribution, insulin sensitivity, or lipid status of obese young men.

Impaired modulation of hepatic glucose output overnight after a 72-h fast in normal man

We have previously reported a 25% fall in glucose utilization (Rd) and glucose production (Ra) in normal volunteers during an overnight fast, when glycogenolysis accounts for approximately 70% of hepatic glucose output (HGO). This reduction in Ra and Rd was positively correlated with reductions in glycerol and FFA. To determine if a similar fall in HGO occurs after a prolonged fast when HGO depends solely upon gluconeogenesis, seven normal male volunteers were fasted for 72 h. Glucose kinetics were then assessed overnight using a [3-3H]glucose infusion from 2200-0800 h. Plasma glucose (3.6 +/- 0.1 mM), immunoreactive insulin (2.7 +/- 0.4 mU/L), C-peptide (0.22 +/- 0.03 nmol/l), Rd (1.30 +/- 0.03 mg/kg.min), and Ra (1.28 +/- 0.03 mg/kg.min) were suppressed, and plasma glucagon (98.8 +/- 13.2 pmol/L) was elevated compared to values obtained during the overnight fast, but none of these parameters changed overnight after the 3-day fast. Plasma lactate (0.98 +/- 0.09 mmol/L) and alanine (0.18 +/- 0.03 mmol/L) levels were also unchanged throughout the night. Plasma glycerol (0.14 +/- 0.03 mmol/L) and FFA (0.98 +/- 0.07 mmol/L) were significantly elevated compared to values during the overnight fast, but failed to fall during the study as had been observed during a 14-h fast. We conclude that the modulation of HGO observed during an overnight fast does not occur during prolonged fasting. The lack of nocturnal modulation of HGO when plasma FFA and glycerol levels are fixed at elevated concentrations supports a role of FFA and/or glycerol in the modulation of HGO during an overnight fast.

The central role of obesity (hyperinsulinemia) in the pathogenesis of the polycystic ovary syndrome

Insulin resistance and hyperinsulinemia appear to be almost universal features of the polycystic ovary syndrome. We propose that obesity permits full phenotypic expression of the polycystic ovary syndrome in women predisposed to develop this condition by generating an insulin-resistant, and consequently hyperinsulinemic, state. The resultant hyperinsulinemia may produce hyperandrogenism by affecting multiple facets of androgen metabolism.

Suppression of serum dehydroepiandrosterone sulfate levels by insulin: an evaluation of possible mechanisms

We previously demonstrated a progressive decline in serum dehydroepiandrosterone sulfate (DHEA-S) levels in women during a hyperinsulinemic-euglycemic clamp. To determine whether this fall in serum DHEA-S levels might have been due to insulin-stimulated 1) hydrolysis of DHEA-S to dehydroepiandrosterone (DHEA), 2) conversion of DHEA-S/DHEA to androstenedione, and/or 3) urinary excretion of these steroids, 10 additional men were studied by the hyperinsulinemic-euglycemic clamp technique. Each man received a 0.1 U/kg (0.72 nmol/kg) insulin bolus dose, followed by a 10 mU/kg.min (72 pmol/kg.min) insulin infusion for 4 h. An average insulin level of 12,390 +/- 259 (+/- SE) pmol/L (1,726.8 +/- 36 microU/mL) was achieved; serum glucose was maintained at 5.0 +/- 0.1 mmol/L (90.5 +/- 2.3 mg/dL). During the hyperinsulinemia, serum DHEA-S levels fell progressively and were significantly lower than baseline at 4 and 6 h of study (85.5 +/- 5.9% and 79.1 +/- 3.2% of baseline values, respectively; P less than 0.05). Serum DHEA levels fell concurrently and were significantly lower than baseline at 2, 4, and 6 h of study (66.2 +/- 12.3%, 61.6 +/- 11.2%, and 52.9 +/- 10.2% of baseline values, respectively; P less than 0.05). The percent fall in serum DHEA levels correlated positively with the percent fall in serum DHEA-S levels (r = 0.44; P less than 0.02). Serum androstenedione levels also fell progressively during hyperinsulinemia and were significantly lower than baseline at 2, 4, and 6 h of study (71.5 +/- 4.1%, 71.0 +/- 7.2%, and 48.1 +/- 3.3% of baseline values, respectively; P less than 0.05). No change in serum DHEA-S, DHEA, or androstenedione levels occurred in paired control studies, during which 0.45% saline was infused at rates matched exactly to the rates of the dextrose and insulin infusions during the hyperinsulinemic clamp studies. Despite decreasing serum DHEA-S and DHEA levels during hyperinsulinemia, urinary DHEA-S and DHEA glucuronide excretions were increased by 50% (P less than 0.05) and 86% (P = 0.05), respectively, compared to urinary excretion of these steroids during control studies. In contrast, urinary excretion of unconjugated DHEA was unchanged. Quantitatively, however, increased urinary excretion of conjugated DHEA during hyperinsulinemia accounted for only about 5% of the concomitant fall in serum DHEA-S concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Accelerated decline in hepatic glucose production during fasting in normal women compared with men

Plasma glucose values have been reported to be lower in women than in men after a 72-hour fast. However, a comparison of glucose kinetics in fasting men and women has not been described. Therefore, five normal men and five normal women underwent sequential 3-3H-glucose infusions after both a 14- and a 64-hour fast. Plasma glucose levels fell similarly during the fast in men (5.23 +/- 0.03 v 3.96 +/- 0.14 mmol/L, P less than .01) and women (4.84 +/- 0.14 v 3.65 +/- 0.25 mmol/L, P less than .01). The fall in plasma glucose was associated with a significantly greater fall in glucose appearance (Ra) in women compared with men (P less than .05). Ra fell 15.8% +/- 3.0% in men (2.11 +/- 0.24 to 1.79 +/- 0.24 mg.kg-1.min-1, P less than .01) and 24.6% +/- 1.4% in women (2.22 +/- 0.17 to 1.67 +/- 0.12 mg.kg-1.min-1, P less than .001). During the fast, plasma glycerol, free fatty acids (FFA), and beta-hydroxybutyrate levels rose significantly and plasma alanine fell significantly in both sexes. Plasma glycerol levels were significantly higher in women compared with men after fasting (0.16 +/- 0.01 v 0.11 +/- 0.02 mmol/L, P less than .05). In addition, the transition from ambulation to bed rest demonstrated unexpected sex-related differences in glucose homeostasis after the 64-hour fast. During the two-hour equilibration period required for glucose kinetic studies (subjects reclining), significant decrements in glucose, FFA, and lactate were observed in the 64-hour fasted women but not in the men.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation of serum molindone levels to serum prolactin levels and antipsychotic response

The antipsychotic drug molindone is considered to be atypical in its mode of action and to have mild side effects. Currently no data are available on the range of serum levels of this drug during treatment. By means of a high performance liquid chromatographic technique, serum molindone levels were measured in 14 psychotic patients receiving a wide range of doses of this drug. Molindone levels as high as 350 ng/mL were obtained and were not associated with any toxic effects. Significant relations were noted between the serum level of the drug and both serum prolactin level and treatment response. The authors suggest that molindone may have a range of serum levels consistent with therapeutic benefit. Serum molindone and prolactin levels might help assess resistance to molindone treatment.

Suppression of serum insulin by diazoxide reduces serum testosterone levels in obese women with polycystic ovary syndrome

To test the hypothesis that insulin plays a role in the hyperandrogenism of obese women with polycystic ovary syndrome, we conducted a prospective study in which the androgen status of five obese women with polycystic ovary syndrome was assessed on two occasions: before and after 10 days of oral diazoxide (100 mg, three times daily) administration. Fasting serum insulin levels decreased from 177 +/- 45 (+/- SE) to 123 +/- 43 pmol/L (P less than 0.01) and insulin release in response to 100 g oral glucose administration decreased from 223.0 +/- 29.2 to 55.6 +/- 7.9 nmol.min/L (P less than 0.002) after diazoxide administration. At the same time, serum total testosterone fell from 2.5 +/- 0.4 to 2.1 +/- 0.3 nmol/L (P less than 0.007), serum testosterone not bound to sex hormone-binding globulin fell from 1.9 +/- 0.3 to 1.4 +/- 0.2 nmol/L (P less than 0.01), and the molar ratio of serum androstenedione to serum estrone fell from 25.7 +/- 7.7 to 16.6 +/- 5.5 (P less than 0.04). Serum sex hormone-binding globulin levels increased slightly but not significantly from 13.2 +/- 1.0 to 21.7 +/- 4.1 nmol/L. Serum androstenedione, dehydroepiandrosterone sulfate, estradiol, estrone, and progesterone concentrations did not change, nor did basal or GnRH-stimulated serum LH and FSH concentrations. These results suggest that hyperinsulinemia in obese women with polycystic ovary syndrome may directly increase serum testosterone levels.

Morning insulin requirements. Critique of dawn and meal phenomena

Morning insulin resistance has frequently been invoked to explain early-morning increases in both basal and breakfast-associated insulin requirements in diabetic patients. This increase in insulin requirements and plasma glucose from 0600 to 0900, when compared with midnight to 0600, has been termed the dawn phenomenon. We believe that the increased need for insulin in the morning has been misinterpreted. Data are reviewed that suggest the major perturbation overnight is a sleep-associated fall in hepatic glucose output, with a return to basal production rates on arousal in the morning. Moreover, the apparent increased insulin requirement for breakfast compared with lunch or supper (meal phenomenon) appears to be related more to lack of residual insulin effect from a preceding meal than to any putative morning insulin resistance. Thus, we found little evidence to support morning insulin resistance as a cause of either the dawn phenomenon (more appropriately designated the sleep phenomenon) or the meal phenomenon. A proper understanding of these phenomena is essential to the management of diabetic patients receiving insulin.

Sleep-associated fall in glucose disposal and hepatic glucose output in normal humans. Putative signaling mechanism linking peripheral and hepatic events

Values reported for basal hepatic glucose production and glucose utilization do not reflect metabolic changes occurring during sleep. To determine the effect of sleep with its associated lowered metabolic rate and thermogenesis on glucose kinetics and gluconeogenic substrate availability, 11 normal volunteers underwent an overnight study in which [3-3H]glucose was infused. Despite decreased insulin secretion, a fall in hepatic glucose output was observed with sleep that was synchronous with a reduction in glucose utilization and lipolysis (decreased plasma glycerol and free fatty acids). When activity was increased, these parameters rose toward previously reported basal levels. Prevention of sleep in 6 additional subjects attenuated the fall in glucose utilization and production as well as the fall in glycerol and free fatty acids despite similar insulin and counterregulatory hormone profiles. We suggest that sleep-associated metabolic changes produce a peripheral signal(s) that modulates hepatic glucose production in humans.

Model to examine pathways of carbon flux from lactate to glucose at the first branch point in gluconeogenesis

The first branch point in gluconeogenesis occurs at the conversion of pyruvate to oxaloacetate. To determine the amount of lactate carbon reaching glucose via the direct pyruvate carboxylase pathway versus the tricarboxylic acid cycle, adult rat hepatocytes in primary culture were incubated for 2 h with one of the following isotopic substrates: [1-14C]lactate, [U-14C]lactate, or [1,2-14C]acetate. Production of 14CO2 and [14C]glucose from each substrate was assessed. The amount of lactate carbon 2 and 3 incorporated into glucose or oxidized to CO2 was determined by subtracting values using [1-14C]lactate from those using [U-14C]lactate. After quantitation of CO2 formed from carbons 2 and 3 of lactate, the amount of these carbons incorporated into glucose via the tricarboxylic acid cycle can be determined by simple proportionality from the ratio of label incorporated into glucose or CO2 from [1,2-14C]acetate. The remaining carbons 2 and 3 of lactate incorporated into glucose are derived from the pyruvate carboxylase pathway directly. Ethanol which on oxidation provides NADH and acetate decreased lactate oxidation and enhanced the pyruvate carboxylase pathway. Glucagon increased carbon flux through both pathways but primarily through the pyruvate carboxylase pathway. In summary, a simple model is presented to examine carbon flux from lactate via the pyruvate carboxylase and tricarboxylic acid pathways during gluconeogenesis.

Absorption characteristic of breakfast determines insulin sensitivity and carbohydrate tolerance for lunch

To test the hypothesis that prolonging absorption of breakfast might improve the glucose tolerance of the subsequent meal served at lunch, normal male volunteers were administered the same carbohydrate in either a rapidly absorbed (sucrose, S) or slowly absorbed (sucrose with guar, S + G) form for breakfast (0800) and lunch (1145). Area under the curve (AUC) for glucose did not differ for S at breakfast vs. S + G at breakfast, although AUCinsulin for S at breakfast was greater than that for S + G at breakfast (3389 +/- 608 vs. 1523 +/- 246 microU.min.ml-1, P less than .002). Plasma glucose and insulin profiles for the two breakfast meals differed markedly. Once S was ingested, plasma glucose and insulin returned to baseline after 120 and 160 min, respectively. However, once S + G was ingested, plasma glucose and insulin were still significantly above baseline values after 180 min. When S was eaten for breakfast, AUCglucose for lunch was similar to that for breakfast, regardless of whether lunch consisted of S or S + G. However, if S + G was eaten for breakfast, AUCglucose for S + G or S at lunch was 44% (P less than .005) and 75% of that for breakfast, respectively. Only one of five subjects who ingested S + G for breakfast failed to exhibit a fall in AUCglucose when S was eaten for lunch. The beneficial effect of prolonged absorption of breakfast on the glucose tolerance of lunch was not observed if the timing of lunch was delayed by 2 h (i.e., served at 1345).(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced insulin clearance in normal subjects due to extreme hyperinsulinemia

Insulin clearance was assessed in five normal subjects infused with insulin at a rate of 10 mU.kg-1.min-1 for 12-16 hours, which produced insulin levels of 1500-2000 microU/ml (approximately 10(-8) M). This level approximates the Kd of low affinity insulin binding sites, whereas previous clearance studies had been performed at insulin concentrations of 10(-9) M or less, approximating the Kd of the high affinity insulin receptor. The metabolic clearance rate for insulin during the infusion averaged 214 +/- 29 ml.min-1.m-2, which is half of that reported previously when lower insulin levels were achieved. Upon termination of the insulin infusion, the disappearance of insulin was markedly prolonged with an average "half-life" of 62 minutes. The rapidity with which hyperinsulinemia altered clearance suggested that down-regulation of insulin receptors was probably not the explanation for the reduced clearance. To elucidate the cause for the observed decrease in insulin clearance, five additional subjects were studied. If insulin was infused for 3.0-4.5 hours, the half-life of insulin disappearance was intermediate between that for an insulin bolus dose and that for a 12-16 hour insulin infusion. Administration of an insulin bolus dose at the end of a 12-hour infusion, while the insulin concentration was still approximately 10(-8) M, or 140 min later, when the insulin concentration was 10(-9) M, was followed by rapid disappearance with half-lives of 1.5 and 6-8 minutes, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyrotropin-induced hyperthyroidism: evidence for a common progenitor stem cell

A 36-year-old woman with hyperthyroidism, elevated blood thyroid-stimulating hormone (TSH) and alpha-subunit levels, amenorrhea, hyperprolactinemia and no evidence of acromegaly, was found to have a pituitary adenoma containing TSH, alpha-subunit and growth hormone by immunohistochemistry. Preoperative testing revealed elevated TSH and alpha-subunit with no response to thyrotropin-releasing hormone (TRH) but a normal response in prolactin to TRH. Culture of the pituitary cells showed release of TSH, alpha-subunit and prolactin. In vitro, TRH failed to cause TSH discharge; however, it increased prolactin concentrations in the culture medium. Triiodothyronine, added to the pituitary cell culture, resulted in no inhibition of TSH and prolactin discharge. By electron microscopy, the adenoma cells showed features of thyrotrophs. However, some adenoma cells contained fibrous bodies characteristic of some growth hormone cell tumors and acidophil stem cell adenomas, suggesting that the adenoma originated in a common progenitor cell.

Dehydroepiandrosterone reduces serum low density lipoprotein levels and body fat but does not alter insulin sensitivity in normal men

To assess the effects of dehydroepiandrosterone (DHEA) on body fat mass, serum lipid levels, and tissue sensitivity to insulin, five normal men were given placebo and five normal men were given oral DHEA [1600 mg/day (554.7 mmol/day)] for 28 days in a randomized, double blind study. In the DHEA group serum DHEA-S levels rose 2.5- to 3.5-fold, and mean (+/- SEM) serum androstenedione rose from 4.3 +/- 0.6 to 8.6 +/- 1.2 nmol/L (P less than 0.004, by paired t test), but serum total testosterone, free testosterone, sex hormone-binding globulin, estradiol, and estrone levels did not change. In the DHEA group the mean percent body fat decreased by 31%, with no change in weight. This suggests that the reduction in fat mass was coupled with an increase in muscle mass. DHEA administration also resulted in a fall in mean serum total cholesterol concentration (4.82 +/- 0.21 vs. 4.48 +/- 0.29 nmol/L; P less than 0.05), which was due almost entirely to a fall of 7.5% in mean serum low density lipoprotein cholesterol (3.21 +/- 0.11 vs. 2.97 +/- 0.14 nmol/L; P less than 0.01). No changes in anthropometric parameters or serum lipid levels occurred in the placebo group. Tissue sensitivity to insulin, assessed by the hyperinsulinemic-euglycemic clamp technique, did not change in either the placebo or DHEA groups. These results suggest that in normal men DHEA administration reduces body fat, increases muscle mass, and reduces serum low density lipoprotein cholesterol levels. Tissue sensitivity to insulin was unaffected by short term DHEA administration.

Prolonged insulin resistance following insulin-induced hypoglycaemia

Nineteen normal male volunteers underwent a 10-h glucose clamp study to examine the duration and mechanism of insulin resistance after hypoglycaemia. Dextrose delivery by the Biostator to maintain the target blood glucose level fell below baseline 2 h after induction of hypoglycaemia and remained suppressed for at least 7 h after insulin hypoglycaemia. Insulin secretion as manifested by C-peptide levels remained suppressed for 3-4 h after insulin hypoglycaemia despite return of blood glucose to baseline by 90 min. Glucose kinetic data (3-3H-glucose) performed in six of the subjects indicated that the prolonged insulin resistance was due to significantly increased hepatic glucose production and to suppressed glucose utilisation, persisting for at least 4 h after counterregulatory hormone levels had returned to normal. Post-hypoglycaemic insulin resistance as determined by dextrose delivery was markedly attenuated and the rise in hepatic glucose output totally eliminated in five hypopituitary subjects without growth hormone or cortisol responses to hypoglycaemia. We conclude that post-hypoglycaemic insulin resistance occurs in non-diabetic subjects and persists for at least 7 h following hypoglycaemia. This prolonged insulin resistance is largely related to release of growth hormone and cortisol.

Effects of extreme hyperinsulinaemia on serum levels of trace metals, trace metal binding proteins, and electrolytes in normal females

In order to assess the possible effects of insulin on serum concentrations of trace metals (iron, copper, zinc) and trace metal binding proteins (ferritin, transferrin, coeruloplasmin), five normal females were studied with the hyperinsulinaemic-euglycaemic clamp technique. A 0.1 U/kg insulin bolus was administered, followed by an insulin infusion at a rate of 10 mU/kg/min for 12-16 h. Insulin levels of 1500-2000 microU/ml (9.21-12.28 nmol/l) were attained. When iron levels in serum were assayed colorimetrically, there appeared to be a progressive rise in the mean concentration during the course of the insulin infusion. Direct analysis of serum samples by atomic absorption spectrophotometry also showed that the level of non-haeme iron increased 3-fold in the serum of the subject with the lowest concentration of this metal at the start of the study. In contrast with the results for serum iron, the levels of ferritin, total iron binding capacity (transferrin), zinc, copper and coeruloplasmin were not altered in any subject during the insulin infusion or at 24 h following discontinuation of the infusion. Within 4 h of institution of the hyperinsulinaemic clamp significant reductions in serum levels of potassium, phosphorus, cholesterol, total protein and albumin were noted. As the insulin infusion progressed, the urea nitrogen, uric acid and bicarbonate levels fell as well. These observations suggest that supraphysiologic hyperinsulinaemia of 12-16 h duration may alter serum levels of iron, but not serum levels of zinc, copper or trace metal binding proteins in some individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of hyperinsulinemia on serum testosterone, progesterone, dehydroepiandrosterone sulfate, and cortisol levels in normal women and in a woman with hyperandrogenism, insulin resistance, and acanthosis nigricans

Insulin may mediate the hyperandrogenism that frequently occurs in patients with insulin-resistant states. To test this hypothesis, we studied five normal women and one woman with hyperandrogenism, insulin resistance, and acanthosis nigricans with the hyperinsulinemic-euglycemic clamp technique. Each woman received a 0.1 U/kg insulin bolus dose, followed by a 10 mU/kg X min insulin infusion for 12-16 h. In the normal women, an average insulin level of 1832 +/- 292 (+/- SEM) microU/ml was achieved; serum glucose was clamped at 116 +/- 5 mg/dl. At this level, insulin may bind to the insulin-like growth factor I receptor as well as to its own receptor. Contrary to our working hypothesis, a rise in serum testosterone did not occur in any women during insulin infusion, and in one women, serum testosterone levels decreased. When analyzed as a percentage of the basal value, serum progesterone levels fell 20% in the normal women within the first 2 h of insulin infusion, but did not change thereafter. Dehydroepiandrosterone sulfate (DHEA-S) levels, however, uniformly and progressively decreased by 39% after 12 h of insulin infusion in the normal women and by 31% at 14 h in the woman with hyperandrogenism, insulin resistance, and acanthosis nigricans. The fall in serum DHEA-S levels was not due to diurnal rhythmicity, as the changes in serum DHEA-S levels did not correlated with those in serum cortisol. Suppression of PRL release also was excluded as a cause of the fall in DHEA-S levels. These results indicate that acute hyperinsulinemia of 12- to 16-h duration does not increase serum testosterone or DHEA-S concentrations and, indeed, can cause a decline in serum DHEA-S levels in both normal women and the single woman studied with hyperandrogenism, insulin resistance, and acanthosis nigricans.

Insulin processing by cultured hepatocytes

The chloroquine-sensitive and chloroquine-insensitive steps in insulin degradation by cultured hepatocytes have been explored by employing low temperature to retard processing. Under standard conditions (90 min association and 60 min dissociation) chloroquine inhibited insulin degradation at 15 degrees C but not at 37 degrees C. However, if the association and dissociation periods were short so that only early degradation was examined, marked inhibition of insulin degradation by chloroquine could also be observed at 37 degrees C. This inhibitory effect was observed only during the first 15 min, being masked by increased insulin degradation subsequently. An increase in slowly dissociable insulin, as well as a twofold increase in volume density of multivesicular bodies (MVB), occurred in the presence of chloroquine at both 37 and 15 degrees C. Rapid insulin processing from the slowly dissociable compartment at 37 degrees C masked chloroquine's effect on insulin processing under usual conditions at that temperature. At physiological temperature the chloroquine-sensitive step is not obligatory for insulin degradation by hepatocytes.

Amphetamine response in borderline patients

The behavioral and biological responses to d-amphetamine have been studied extensively in patients with schizophrenia and depression, and to a lesser degree in bipolar affective disorders. Because of theories linking borderline personality disorder to those illnesses, amphetamine, 30 mg, p.o., was administered to eight borderline patients in a double-blind, placebo-controlled study and the results were compared to the responses of normal subjects under identical conditions. Amphetamine led to symptoms of psychosis in four out of eight (50%) borderline patients. No normal subject became psychotic during the procedure. Global ratings of well-being were significantly elevated in the borderline group compared to the normal group. In addition the global response was highly inversely correlated with the patient's score on the Diagnostic Interview for Borderlines. Borderline patients had a nonsignificantly decreased growth hormone response following amphetamine compared to normals. Thus, borderline patients appear to be pharmacodynamically separable from normals.

Sleep apnea in active acromegaly

Previous case reports have shown an association between acromegaly and the sleep apnea syndrome (SAS). Some of the patients described had central SAS, raising the possibility that an elevation of the growth hormone (GH) level may cause a defect in respiratory drive. We determined the prevalence of SAS in 21 patients with a history of acromegaly. We separated them into two groups based on serum GH concentrations. Ten patients had active acromegaly (mean GH concentration, 62.2 ng/mL; range, 12.6 to 148 ng/mL), while 11 patients had inactive acromegaly (mean GH, 3.2 ng/mL; range, 0.7 to 6.4 ng/mL). Four of the ten patients with active acromegaly had SAS; none of the 11 patients with inactive acromegaly had SAS. Three patients with SAS had the purely obstructive type, and one had the mixed central and obstructive type. The hypercapnic ventilatory response was normal in all patients tested and was not influenced by the GH level. We conclude that SAS is associated with active acromegaly and that the GH level does not affect the hypercapnic ventilatory response. The absence of SAS in successfully treated patients suggests that it may resolve after a normal GH level is restored.

Pump-induced insulin aggregation. A problem with the Biostator

A fall in plasma IRI despite constant C-peptide levels during prolonged insulin euglycemic clamp studies using the Biostator (Ames Division, Miles Laboratories, Elkhart, Indiana) prompted a meticulous evaluation of the Biostator's insulin delivery system. At slow infusion rates, a striking loss of immunoreactive and biologically active insulin was observed after 6 h of the Biostator run. Studies with labeled insulin indicated that the loss of insulin was not due to adsorption of insulin to the tubing since recovery of labeled insulin was close to 100%. A variety of techniques (gel filtration, polyacrylamide gel electrophoresis, centrifugation, and Coomassie Brilliant Blue protein assay) indicated that the loss of insulin activity was due to insulin coming out of solution. The insoluble nature of the immunologically and biologically inactive insulin was confirmed by centrifugation, i.e., 88% 125I-insulin precipitated into the pellet. The dependency of this loss of insulin activity on flow rate was clearly demonstrable with activity (IRI) less than 20% of expected at flow rates of 2.1 ml/h, and 30% at 4.2 ml/h. Full recovery was observed only with flow rates of 16.8 ml/h or greater. At each flow rate, IRI rose only after delivery of the effluent between the pump and exit port, demonstrating that insulin alteration occurs within the pump assembly presumably from heat-induced aggregation. Investigators employing the Biostator should carefully examine their systems for this time- and flow rate-dependent alteration of insulin. The loss of IRI at low flow rates (low-dose insulin clamp or insulin delivery during basal periods) will profoundly influence data generated from the Biostator.