Controlled intramolecular antagonism as a regulator of insulin receptor maximal activity

In the treatment of insulin-dependent diabetes the risk of a fatal insulin overdose is a persistent fear to most patients. In order to potentially reduce the risk of overdose, we report the design, synthesis, and biochemical characterization of a set of insulin analogs designed to be fractionally reduced in maximal agonism at the insulin receptor isoforms. These analogs consist of native insulin that is site-specifically conjugated to a peptide-based insulin receptor antagonist. The structural refinement of the antagonist once conjugated to insulin provided a set of partial agonists exhibiting between 25 and 70% of the maximal agonism of native insulin at the two insulin receptor isoforms, with only slight differences in inherent potency. These rationally-designed partial agonists provide an approach to interrogate whether control of maximal activity can provide glycemic control with reduced hypoglycemic risk.

Effects of subcutaneous, low-dose glucagon on insulin-induced mild hypoglycaemia in patients with insulin pump treated type 1 diabetes

AIM

To investigate the dose-response relationship of subcutaneous (s.c.) glucagon administration on plasma glucose and on counter-regulatory hormone responses during s.c. insulin-induced mild hypoglycaemia in patients with type 1 diabetes treated with insulin pumps.

METHODS

Eight insulin pump-treated patients completed a blinded, randomized, placebo-controlled study. Hypoglycaemia was induced in the fasting state by an s.c. insulin bolus and, when plasma glucose reached 3.4 mmol/l [95% confidence interval (CI) 3.2-3.5], an s.c. bolus of either 100, 200, 300 µg glucagon or saline was administered. Plasma glucose, counter-regulatory hormones, haemodynamic variables and side effects were measured throughout each study day. Peak plasma glucose level was the primary endpoint.

RESULTS

Plasma glucose level increased significantly by a mean (95% CI) of 2.3 (1.7-3.0), 4.2 (3.5-4.8) and 5.0 (4.3-5.6) mmol/l to 6.1 (4.9-7.4), 7.9 (6.4-9.3) and 8.7 (7.8-9.5) vs 3.6 (3.4-3.9) mmol/l (p < 0.001) after the three different glucagon doses as compared with saline, and the increase was neither correlated with weight nor insulin levels. Area under the plasma glucose curve, peak plasma glucose, time to peak plasma glucose and duration of plasma glucose level above baseline were significantly enhanced with increasing glucagon doses; however, these were not significantly different between 200 and 300 µg glucagon. Free fatty acids and heart rates were significantly lower initially after glucagon than after saline injection. Other haemodynamic variables, counter-regulatory hormones and side effects did not differ between interventions.

CONCLUSIONS

An s.c. low-dose glucagon bolus effectively restores plasma glucose after insulin overdosing. Further research is needed to investigate whether low-dose glucagon may be an alternative treatment to oral carbohydrate intake for mild hypoglycaemia in patients with type 1 diabetes.

Congenital hyperinsulinism in an infant with paternal uniparental disomy on chromosome 11p15: few clinical features suggestive of Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is the most common congenital overgrowth syndrome involving tumor predisposition. BWS is caused by various epigenetic or genetic alterations that disrupt the imprinted genes on chromosome 11p15.5 and the clinical findings of BWS are highly variable. Hyperinsulinemic hypoglycemia is reported in about half of all babies with BWS. We identified an infant with diazoxide-unresponsive congenital hyperinsulinism (HI) without any apparent clinical features suggestive of BWS, but diagnosed BWS by molecular testing. The patient developed severe hyperinsulinemic hypoglycemia within a few hours after birth, with macrosomia and mild hydronephrosis. We excluded mutations in the K(ATP) channel genes on chromosome 11p15.1, but found a rare homozygous single nucleotide polymorphism (SNP) of ABCC8. Parental SNP pattern suggested paternal uniparetal disomy in this region. By microsatellite marker analysis on chromosome 11p15, we could diagnose BWS due to the mosaic of paternal uniparental disomy. Our case suggests that some HI of unknown genetic etiology could involve undiagnosed BWS with no apparent clinical features, which might be diagnosed only by molecular testing.

Infertility and pregnancy in women with polycystic ovary syndrome

Management of polycystic ovary syndrome (PCOS) usually spans a woman's reproductive years. While treatment of androgenic symptoms is often a primary concern, periodically, the regimen has to be modified because of a desire for pregnancy. At this time the couple should be evaluated for factors that may contribute to infertility and this should include semen analysis. However, for many, anovulation is likely to be the cause of infertility and ovulation induction is generally required. The premise on which ovulation induction in PCOS is based is two-fold: increasing ovarian exposure to follicle stimulating hormone (FSH) and/or correcting hormonal derangements. Potential differences in pathogenesis, evidenced clinically by phenotypic diversity, would suggest that treatment should be individualized. After a brief overview of factors relating to infertility, this paper outlines treatments available for ovulation induction in women with PCOS and provides a critical appraisal of management options. These options include the use of clomiphene citrate, insulin sensitizers, and the combination. Protocols for ovulation induction with FSH injections are outlined and the relative risks of multiple gestation and severe ovarian hyperstimulation syndrome of these various protocols discussed. The use of aromatase inhibitors and the occasional use of glucocorticoids are briefly reviewed, and indications for in vitro fertilization and laparoscopic ovarian diathermy outlined. Pregnancy outcome in this patient population is also discussed.

Weight loss in obese men by caloric restriction and high-dose diazoxide-mediated insulin suppression

OBJECTIVE

To examine the concept whether high-dose diazoxide (DZX)-mediated insulin suppression, in combination with moderate caloric restriction and increased physical activity, can establish a weight loss of at least 15% in obese hyperinsulinaemic men.

DESIGN

Open, uncontrolled, 6-month pilot study. Energy intake was reduced by 30%, and walking for at least 30 min a day was strongly recommended. DZX treatment was started at 50 mg t.i.d. and increased by 50 mg per dose every 4 weeks to a maximum of 300 mg t.i.d., unless hyperglycaemia or other side-effects occurred.

SUBJECTS AND METHODS

Eighteen obese hyperinsulinaemic men with a body mass index of 30-35 kg/m(2). Measurements included body weight, body composition, blood pressure, glycaemic control, insulin response, adiponectin and serum lipids.

RESULTS

Body weight decreased by 9.4 kg (95% CI: 5.6-13.2 kg, p < 0.001), waist circumference reduced by 9.2 cm (95% CI: 5.3-12.9 cm, p < 0.001) and total body fat mass decreased by 23.3% (95% CI: 13.7-32.9%, p < 0.001), without a concomitant change in soft tissue lean body mass or bone mass. Fat loss was inversely related to fasting insulin levels achieved at 6 months (r = -0.76, p < 0.002). Diastolic blood pressure decreased by 10.9 mmHg (95% CI: 6.5-15.4 mmHg, p < 0.002). Fasting and postmeal peak insulin levels were reduced by about 65% (p < 0.001) and decreased to the normal range for non-obese men. Fasting and postmeal peak glucose levels increased by 0.8 +/- 0.3 mmol/l (p = 0.01) and 1.4 +/- 0.7 mmol/l (p = 0.06) respectively. Haemoglobin A1c rose by 0.5% to 5.9 +/- 0.2%.

CONCLUSION

High-dose DZX-mediated insulin suppression, in combination with moderate caloric restriction and lifestyle advice, is associated with a clinically relevant degree of weight reduction. A more extensive exploration is warranted to optimize this mode of treatment and to further clarify its risks and benefits.

Effect of pioglitazone and its combination with statins in coronary artery disease patients with hyperinsulinemia

The objective of the study was to demonstrate the effect of pioglitazone and pioglitazone in combination with statin on East Indian patients with hyperinsulinemia and hyperlipidemia. It was a randomized, placebo-controlled, double-blind study with a parallel-group design comprising 83 patients. Patients of either sex with cardiac complications, including hyperlipidemia and (or) diabetes mellitus with or without hyperinsulinemia, were enrolled. Patients over 70 years of age, with renal or hepatic failure, or with severe diabetes mellitus (total glucose >400 mg/dL) were excluded from the study. Enrolled patients were randomly assigned to 4 groups that received placebo, pioglitazone, atorvastatin, or both. Blood samples were collected before and after treatment for analysis of serum glucose, insulin, lipid profile, apolipoprotein (apo) A1, apo B, and fibrinogen. Data were compared with that of patients with normal insulin or hyperinsulinemia. The patients with hyperinsulinemia receiving only pioglitazone showed a significant decrease in insulin levels compared with those with normal insulin levels. These patients also showed a significant increase in HDL levels. However, no significant change was observed in patients treated with both atorvastatin and pioglitazone. Pioglitazone was also found to increase significantly the apo A1 levels in patients with hyperinsulinemia, but there was no significant increase in patients given both atorvastatin and pioglitazone. Our data suggests that pioglitazone should be given preferably to the patients with hyperinsulinemia and statin should not be coadministered.

No effect of inhibition of insulin secretion by diazoxide on weight loss in hyperinsulinaemic obese subjects during an 8-week weight-loss diet

AIM

Obesity is positively associated with hyperinsulinaemia, and it has been suggested that hyperinsulinaemia may contribute to maintain the obese state in insulin-resistant obese individuals. The aim of the present study was to investigate the effect of inhibition of insulin secretion by diazoxide on weight loss in obese, normoglycaemic (fasting plasma glucose of > or =6.1 mmol/l), hyperinsulinaemic (fasting plasma insulin of > or =100 pmol/l) adults during a 2.5 MJ/day energy-deficient diet.

METHODS

In an 8-week, double-blind, placebo-controlled parallel design, 35 overweight and obese subjects (age: 23-54 years, body mass index: 27-66 kg/m(2)) were randomized either to 2 mg/kg/day (maximum 200 mg/day) of oral diazoxide or to placebo. Body composition and resting energy expenditure (REE) were measured before and after the intervention. Blood samples, and appetite sensations by visual analogue scales, were collected during fasting, during an oral glucose tolerance test (OGTT) and 4 h postprandially after a test meal. Subsequently, an ad libitum meal was given.

RESULTS

Thirty-one subjects completed the protocol. Eight weeks of diazoxide decreased incremental area under the response curve (iAUC) for insulin (iAUC(insulin)) and for C-peptide (iAUC(C-peptide)) and increased iAUC for glucose (iAUC(glucose)) during the OGTT and the test meal compared with the use of placebo (p < 0.003). No differences in changes between the groups in body weight, body fat, REE or appetite were observed during the 8-week trial.

CONCLUSION

These findings do not suggest that hyperinsulinaemia per se contributes to maintenance of the obese state, and insulin secretion inhibition seems not a promising drug target.

The anti-oestrogen ICI 182,780, but not tamoxifen, inhibits the growth of MCF-7 breast cancer cells refractory to long-term oestrogen deprivation through down-regulation of oestrogen receptor and IGF signalling

Long-term culture of MCF-7 wild-type (wt) cells in steroid-depleted medium (LTED) results in hypersensitivity to oestradiol (E2) coinciding with elevated levels of ERalpha and enhanced growth factor signalling. In this study, we aimed to compare the effects of the pure anti-oestrogen ICI 182,780 (ICI) with the competitive anti-oestrogen tamoxifen (TAM) on oestrogen and IGF signalling in these cells. Wt MCF-7 and LTED cells were treated with a log 7 concentration range of E2, TAM or ICI. Effects on cell growth, ERalpha transactivation, expression of ERalpha, ERbeta and components of the IGF pathway were measured with and without insulin. In the presence of insulin, growth of LTED cells was refractory to TAM but inhibited by ICI and E2. In the absence of insulin, LTED cells showed persistent hypersensitivity to E2, and remained inhibited by ICI but were largely unaffected by TAM. ICI but not TAM inhibited ER-mediated gene transcription and treatment with ICI resulted in a dose-dependent reduction in ERalpha levels whilst having no effect on ERbeta expression. IGF-I receptor and insulin receptor substrate 2 levels were increased in LTED versus the Wt MCF-7 cells, and ICI but not TAM reduced their expression in a dose-dependent fashion. Thus IGF signalling as well as ERalpha expression and function are enhanced during LTED. While the resultant cells are resistant to TAM, ICI down-regulates ERalpha, reducing IGF signalling and cell growth. These results support the use of ICI in women with ER-positive breast cancer who have relapsed on an aromatase inhibitor.

Insulin-lowering treatment reduces aromatase activity in response to follicle-stimulating hormone in women with polycystic ovary syndrome

OBJECTIVE

To investigate the effects of reduction of insulin resistance and hyperinsulinemia associated with the polycystic ovary syndrome (PCOS) on FSH-stimulated ovarian aromatase activity.

DESIGN

Prospective study.

SETTING

Academic health center, Siena, Italy.

PATIENT(S)

Twenty women 18 to 26 years of age in whom PCOS was diagnosed on the basis of oligomenorrhea or amenorrhea and hyperandrogenemia.

INTERVENTION(S)

Recombinant FSH was administered. The next day, therapy with metformin (500 mg t.i.d.) was begun. After 35 to 40 days of treatment, the pretreatment protocol was repeated.

MAIN OUTCOME MEASURE(S)

Plasma levels of estradiol (E(2)), androstenedione (A), and testosterone (T). The ratios of basal levels and areas under the curve (AUCs) of products and substrates were compared before and after metformin administration to detect differences in aromatase activity.

RESULT(S)

Metformin treatment was associated with significant reduction in basal free testosterone plasma levels, insulin plasma levels, and insulin response to oral glucose tolerance testing. Administration of FSH was followed by a significantly lesser E(2) response after metformin therapy than before this therapy. The ratios of AUC(E2) to AUC(A) and to AUC(T), indicative of aromatase activity in response to FSH, were significantly lower after metformin therapy than before.

CONCLUSION(S)

Metformin therapy in women with PCOS is associated with a reduction in aromatase activity in response to FSH. Insulin affects production of both androgen and estrogen. Insulin therefore plays a central role in regulating the activity of thecal and granulosa cells.

Naloxone decreases insulin secretion in hyperinsulinemic postmenopausal women and may positively affect hormone replacement therapy

OBJECTIVE

To evaluate the influence of the opioid system on glyco-regulation in postmenopausal women before and after hormone replacement therapy (HRT).

DESIGN

Prospective nonrandomized clinical study.

SETTING

Academic research environment.

PATIENT(S)

Twenty-one healthy normo- or hyperinsulinemic postmenopausal women.

INTERVENTION(S)

Oral glucose tolerance test (OGTT) (saline study), OGTT with IV injection of naloxone (naloxone study), and hyperinsulinemic euglycemic clamp performed before treatment, after 12 weeks of estrogen replacement therapy (ERT), and after 12 additional weeks of estro-progestin combined therapy (i.e., HRT).

MAIN OUTCOME MEASURE(S)

Glucose, insulin, and c-peptide plasma levels assessed in fasting condition and during the two OGTTs (area under the curve [AUC]). Evaluation of fractional hepatic insulin extraction (FHIE) and peripheral sensitivity to insulin.

RESULT(S)

At baseline, there is a greater increase of the FHIE and a more significant reduction of the insulin AUC in the hyperinsulinemic patients during the naloxone study compared with the saline study. In these women, ERT enhanced the c-peptide AUC and improved the FHIE; naloxone infusion mainly increased these two parameters. HRT did not induce any further change.

CONCLUSION(S)

Endogenous opioid peptides are involved in the modulation of carbohydrate metabolism in menopause in hyperinsulinemic patients more than in other patients. The favorable changes of the glyco-insulinemic metabolism induced by HRT may be partially due to the induction of the opioidergic activity.

Effects of D-Chiro-Inositol in Lean Women with the Polycystic Ovary Syndrome

OBJECTIVE

To determine whether the administration of D-chiro-inositol, a putative insulin-sensitizing drug, would affect the concentration of circulating insulin, the levels of serum androgens, and the frequency of ovulation in lean women with the polycystic ovary syndrome.

METHODS

In 20 lean women (body mass index, 20.0 to 24.4 kg/m 2) who had the polycystic ovary syndrome, treatment was initiated with either 600 mg of D-chiro-inositol or placebo orally once daily for 6 to 8 weeks. We performed oral glucose tolerance tests and measured serum sex steroids before and after therapy. To monitor for ovulation, we determined serum progesterone concentrations weekly.

RESULTS

In the 10 women given D-chiro-inositol, the mean (+/- standard error) area under the plasma insulin curve after oral administration of glucose decreased significantly from 8,343 +/- 1,149 mU/mL per min to 5,335 +/- 1,792 mU/mL per min in comparison with no significant change in the placebo group (P = 0.03 for difference between groups). Concomitantly, the serum free testosterone concentration decreased by 73% from 0.83 +/- 0.11 ng/dL to 0.22 +/- 0.03 ng/dL, a significant change in comparison with essentially no change in the placebo group (P = 0.01). Six of the 10 women (60%) in the D-chiro-inositol group ovulated in comparison with 2 of the 10 women (20%) in the placebo group (P = 0.17). Systolic (P = 0.002) and diastolic (P = 0.001) blood pressures, as well as plasma triglyceride concentrations (P = 0.001), decreased significantly in the D-chiro-inositol group in comparison with the placebo group, in which these variables either increased (blood pressure) or decreased minimally (triglycerides).

CONCLUSION

We conclude that, in lean women with the polycystic ovary syndrome, D-chiro-inositol reduces circulating insulin, decreases serum androgens, and ameliorates some of the metabolic abnormalities (increased blood pressure and hypertriglyceridemia) of syndrome X.

Endocrine and metabolic effects of octreotide, a somatostatin analogue, in lean PCOS patients with either hyperinsulinaemia or lean normoinsulinaemia

The effects on insulin secretion and on the glycaemic and androgen status before and after short-term treatment with octreotide were evaluated in 16 normal weight patients with polycystic ovarian syndrome (PCOS). Hyperinsulinaemia was determined by measuring the insulin response after oral glucose tolerance test (OGTT). Seven patients (group A) were classified as normoinsulinaemic, while nine patients (group B) were considered hyperinsulinaemic according to insulin response after OGTT. Octreotide treatment did not modify either glycaemic or insulinaemic response after OGTT, or androgen profile, in normoinsulinaemic patients. On the contrary, a significant decrease in the basal concentrations of luteinizing hormone (LH), testosterone and androstenedione, and a significant increase in serum concentrations of sex hormone-binding globulin (SHBG) were observed in the hyperinsulinaemic group of patients, in which we observed also a significant decrease of insulinaemic response and a decompensation of the glycaemic profile after OGTT. Our study is the first report showing that: (i) octreotide does not appear to significantly influence pituitary release of gonadotrophins in this group of PCOS patients; (ii) octreotide is able to reduce insulin release, LH and androgen concentrations in lean PCOS patients with hyperinsulinaemia. Due to the presence of a decompensation of glucose homeostasis during treatment, octreotide does not seem advisable for long-term therapy of hyperandrogenism in lean PCOS patients with hyperinsulinaemia.

Beta-cell rest: a strategy for the prevention of autoimmune diabetes

An autoantigen being recognized by specific receptors is the key reaction of an autoimmune disease. Whereas much efforts have been made to develop immunosuppressive regimens which reduce the amount of effector cells, and/or inhibit receptor activation, surprisingly little attention has been paid to reduce the ligand-receptor interaction by interfering with the amount of antigen being presented from the target cells. In this review, we discuss clinical observations in autoimmune endocrine disease which illustrate that target cell alterations can modify the disease activity and comment on recent clinical trials which indicate that beta-cell rest may be beneficial to the course of human autoimmune diabetes mellitus.

Effects of insulin reduction with benfluorex on serum dehydroepiandrosterone (DHEA), DHEA sulfate, and blood pressure in hypertensive middle-aged and elderly men

To determine whether a reduction in insulinemia would be associated with a rise in serum dehydroepiandrosterone (DHEA) sulfate in insulin-resistant men, 29 middle-aged (30-59 yr old) and 28 elderly (60-80 yr old) hypertensive men were enrolled into a single blind, placebo-controlled study, in which benfluorex was administered to improve insulin sensitivity and reduce circulating insulin. Men in each age group received either benfluorex (150 mg) or placebo three times daily for 6 weeks, and fasting serum insulin, glucose, DHEA, DHEA sulfate, and cortisol were determined before and after treatment. Glucose tolerance was also assessed by an oral glucose tolerance test. Benfluorex treatment lowered diastolic and systolic blood pressures and improved glucose tolerance in both age groups. In middle-aged men, benfluorex (n = 12) reduced both the area under the curve for glucose (AUCGLUCOSE; from 977 +/- 27 to 814 +/- 27 mmol/L.min; P = 0.0001) and the AUCINSULIN (from 78.1 +/- 7.9 to 44.5 +/- 5.7 nmol/L.min; P < 0.0001) during the oral glucose tolerance test. In elderly men, benfluorex (n = 15) also reduced both the AUCGLUCOSE (from 1100 +/- 60 to 864 +/- 26 mmol/L.min; P < 0.0001) and the AUCINSULIN (from 88.9 +/- 5.6 to 44.8 +/- 5.8 nmol/L.min; P < 0.0001). Concurrent with the reduction in insulinemia, benfluorex treatment was associated with rises in both serum DHEA sulfate and unconjugated DHEA. In middle-aged men, serum DHEA sulfate and DHEA rose from 6.80 +/- 0.75 to 10.52 +/- 1.02 mumol/L (P < 0.015) and from 13.69 +/- 1.95 to 22.78 +/- 2.90 nmol/L (P < 0.03), respectively. In elderly men, serum DHEA sulfate and DHEA rose from 5.16 +/- 0.67 to 8.36 +/- 1.21 mumol/L (P < 0.015) and from 8.47 +/- 0.99 to 22.61 +/- 3.24 nmol/L (P < 0.0005), respectively. In neither middle-aged nor elderly men did serum cortisol change with benfluorex treatment. Neither glucose tolerance nor serum DHEA, DHEA sulfate, or cortisol levels changed in either middle-aged (n = 17) or elderly (n = 13) men treated with placebo. We conclude that benfluorex treatment lowers blood pressure, improves glucose tolerance, reduces the glucose-stimulated insulin response, and increases serum DHEA and DHEA sulfate in both middle-aged and elderly men.(ABSTRACT TRUNCATED AT 400 WORDS)

Insulin antagonistic effects of growth hormone in short children

Growth hormone has several insulin antagonistic effects. To determine the time course of these effects in growth-hormone-treated children, the frequently samples intravenous glucose tolerance test was used to measure insulin sensitivity (SI) and glucose effectiveness (Sg) before, and 1 week, 1 month and 6 months after beginning growth hormone therapy in 3 patients with growth hormone deficiency (GHD), 3 patients with non-growth-hormone-deficient short stature (NGHD) and 3 with Turner syndrome (TS). Pretreatment SI was lower in TS than in the other two groups (p < 0.05), but Sg did not differ between groups. Mean SI levels 1 week and 1 month after starting growth hormone therapy were not different from before growth hormone [1.67 +/- 0.26 x 10(-4) (pmol/l)-1 min-1]. SI after 6 months of growth hormone [0.67 +/- 0.15 x 10(-4) (pmol/l)-1 min-1] was lower than before and 1 week after growth hormone (p < 0.005). SI responses did not differ between groups. Sg, glucose tolerance, blood pressure, triglyceride, and cholesterol levels did not change, but the incremental insulin response increased with growth hormone therapy. Thus, in this small study 6 months of growth hormone therapy decreased SI, but did not affect other cardiovascular risk factors.

Diabetogenic effect of pentamidine. In vitro and in vivo studies in a patient with malignant insulinoma

Pentamidine can cause hypoglycemia followed by hyperglycemia. The mechanism of this biphasic response is not known but has been reported to be similar to that of streptozotocin and N-3-pyridyl-N-p- nitrourea (Vacor). Pentamidine (4 mg/kg per day for 12 days) was used in a patient with malignant insulinoma after several unsuccessful debulking procedures and chlorozotocin therapy. Mean glucose and immunoreactive insulin levels (+/- SEM) before and after therapy were 80 +/- 40 mg/dl versus 70 +/- 50 mg/dl and 216 +/- 12 microU/ml versus 198 +/- 22 microU/ml, respectively. These were not significantly different. The patient's five-month-old malignant insulinoma monolayer cell culture was incubated with pentamidine (60 micrograms/ml) in the presence or absence of supplemented stimulatory medium consisting of glucose (300 mg/dl) and theophylline (20 micrograms/ml). Chloroquine (60 micrograms/ml) was added to inhibit lysosomal degradation of immunoreactive insulin. Aliquots of media for immunoreactive insulin determination were obtained at 30 minutes, 20 hours, 72 hours, and three weeks. The cells were examined by high-power light microscopy at each time interval. At 30 minutes, pentamidine alone caused passive release of immunoreactive insulin, 23 percent higher than control (p less than 0.01). Stimulatory medium increased immunoreactive insulin 45 percent greater than control (p less than 0.01). Pentamidine plus stimulatory medium had no additive effect on immunoreactive insulin released within 30 minutes. At the end of 20 hours, immunoreactive insulin was no different with pentamidine and/or stimulatory medium. However, the addition of chloroquine increased immunoreactive insulin by 35 percent above the medium with pentamidine and stimulatory medium (p less than 0.01). At 72 hours, pentamidine suppressed immunoreactive insulin by 100 percent in all the media, irrespective of the presence or absence of stimulatory medium and/or chloroquine. At the end of three weeks, there was 50 percent suppression of immunoreactive insulin in the control medium, but pentamidine again completely suppressed immunoreactive insulin. High-power microscopy demonstrated intact cells in the control medium, whereas no cell structure could be detected in the media containing pentamidine at three weeks. In summary, pentamidine had no acute in vivo effect in a patient with malignant insulinoma. However, when used in an in vitro monolayer system, pentamidine caused (1) acute immunoreactive insulin release followed by inhibition of immunoreactive insulin secretion and (2) cytolysis of human malignant insulinoma cells in vitro.

Pharmacotherapy of preterm labor

Physiological factors initiating the birth process, problems associated with preterm labor, and use of pharmacotherapeutic agents to treat preterm labor are reviewed. Human parturition appears to be initiated by a combination of factors, the interplay of which is not well understood. In many cases, the threat posed by preterm labor is difficult to assess. Because the stringency of patient-selection criteria varies widely among studies, success rates of different drugs used to arrest labor are difficult to compare. For both short-term and long-term tocolysis, beta 2-sympathomimetic agents (betamimetics) can be used. These drugs, which include isoxsuprine, ritodrine, terbutaline, albuterol, nylidrin, fenoterol, metaproterenol, and hexoprenaline, are believed to affect intracellular calcium concentrations in the myometrium. Ritodrine is the only drug in this class currently approved by the FDA for inhibition of labor. Terbutaline has been shown to be effective in halting uterine contractions and is substantially less expensive than ritodrine. Calcium channel-blocking agents such as nifedipine and verapamil are being investigated for inhibition of labor. Magnesium sulfate, another calcium antagonist, has long been used as a tocolytic. Other agents discussed are ethanol, diazoxide, the prostaglandin synthetase inhibitors (e.g., indomethacin and aspirin), and progestational steroids. Pharmacotherapy should be individualized on the basis of the patient's clinical condition, presence of other disease states, and side effects associated with available tocolytic agents. To date, a betamimetic with selective beta 2 effects, such as terbutaline or ritodrine, is the most valuable agent for inhibition of preterm labor.