Clinical management of the NIDDM patient. Impact of the American Diabetes Association practice guidelines, 1985-1993. Endocrine Fellows Foundation Study Group.

OBJECTIVE: To assess the impact of the American Diabetes Association's (ADA's) standards of care for patients with non-insulin-dependent diabetes mellitus (NIDDM) on practice patterns among university-based endocrine physicians and fellows. RESEARCH DESIGN AND METHODS: This study represents a retrospective chart-based review of 790 patients with NIDDM conducted by endocrine fellows in training at 42 academic institutions. By using an ADA guidelines-based questionnaire, patient management and adherence to the guidelines were assessed by reviewing charts dating > or = 3 years before, the year of, and 3 years after the guidelines' publication. All calculations were performed using the McNemar test, and all P values are two-sided. RESULTS: The ADA standards of care have not had the significant impact in the clinical training setting that was anticipated. Deficiencies were noted in all aspects of the diabetic patient encounter and did not improve significantly following publication of the guidelines, except in the areas of foot care, eye examination, and lipid screening. Major deficiencies exist in areas of quality assurance and chart documentation, and these did not improve over time. CONCLUSIONS: New strategies must be devised to increase awareness and implementation of these guidelines, both to enhance patient care and to improve the training of future diabetes caregivers.

Atherosclerosis in diabetes: the role of hyperinsulinemia.

Non-insulin-dependent diabetes (NIDDM) is a major cause of premature morbidity and mortality among adults. Macrovascular disease of coronary and peripheral vessels is the primary cause of death in these patients. Numerous experimental and epidemiologic studies have suggested that hyperinsulinemia accelerates the development of atherosclerosis. In experimental models, insulin promotes diet-induced lesion development and overrides lesion regression and estrogen protection against atherosclerosis. Local hyperinsulinemia induced by selected arterial infusion accelerates atherosclerosis in the perfused artery. Insulin has been shown to stimulate subintimal smooth muscle and fibroblast cells in culture, and to increase the uptake and local synthesis of lipid by these cells. Insulin may also induce inhibition of fibrinolysis. Several prospective studies performed on nondiabetic patients show that either fasting or postprandial insulin levels are a sensitive predictor of the development of coronary disease independent of other risk factors. Two recent studies in NIDDM patients confirm this finding and suggest that glycemic control may not be a significant factor in the development of macrovascular disease. Diseases of carbohydrate tolerance, ie, NIDDM, impaired glucose tolerance, obesity, are frequently associated with elevated circulating insulin levels, either physiologically or secondary to treatment. Given the high prevalence of cardiovascular disease in these populations, modifying therapy to minimize hyperinsulinemia should be an important consideration in a treatment program. Use of oral agents such as glipizide or gliclazide, which induce less diurnal hyperinsulinemia, may be advantageous when compared to traditional oral agent or insulin therapy.

The metabolic clearance, distribution, and degradation of dimeric and monomeric growth hormone (GH): implications for the pattern of circulating GH forms.

The ratio of oligomeric (big) to monomeric (little) human (h)GH forms in plasma exceeds that in the pituitary gland severalfold. To investigate whether delayed metabolic clearance of oligomers could explain this discrepancy, we measured MCR, distribution volumes, and degradation rates of radio-labeled hGH22K dimer, hGH20K dimer, hGH22K monomer, and hGH20K monomer in the rat. Hormones were injected as a bolus, and disappearance from plasma was followed by immunoprecipitation and trichloroacetic acid precipitation. MCRs of the dimers were significantly lower than those of the corresponding monomers (5-fold in the case of hGH22K, and 2-fold in the case of hGH20K). Both dimers were also degraded at slower rates than the monomers. Distribution volumes for the dimers, although somewhat smaller, were not statistically different from those for the monomers and were consistent with distribution in the extracellular space. We conclude that hGH dimers are relatively protected from degradation and hence cleared more slowly from the blood than hGH monomers. This may lead to their accumulation in the circulation relative to their monomeric counterparts, which may explain their high proportion in plasma as compared to pituitary.

Secretory patterns of growth hormone during basal periods in man.

Human growth hormone (hGH) concentrations in plasma often fall to levels not detectable by RIA. These so-called basal levels prevail during the greater part of the day. Since hGH is involved in the homeostasis of several metabolic processes, it is important to examine its exact plasma concentration and secretory pattern during basal periods. We used an immunoadsorbent technique to extract hGH from large plasma samples to precisely measure basal hGH concentrations and their variation with time. Blood samples (20 mL) were drawn from 12 normal subjects in the fasted and rested state every 15 minutes over a three-hour period. Plasma hGH levels varied over three orders of magnitude (range, 34 to 60,000 pg/mL). During basal periods, episodes of secretory pulses, of moderate sustained secretion, and of complete secretory inactivity occurred. Women had significantly higher overall hGH levels as well as basal hGH levels than men, but no significant sex difference in the pulse frequency during basal periods could be detected in the limited time allotted for study. No convincing relationship was noted between variations in plasma glucose and the secretory pattern of hGH, or vice versa. We conclude that hGH is secreted in an episodic fashion during basal periods. Conceptually, basal and stimulated hGH secretion may be viewed as extremes of a continuous spectrum of pituitary activity, basal hGH levels are lower than heretofore appreciated, the known tendency of women to higher hGH levels is also evident in the basal range, and oscillations in plasma glucose do not affect the microsecretory pattern of hGH, nor are endogenous hGH pulses followed by acute changes in glycemia.

Molecular forms of human growth hormone secreted in vivo: nonspecificity of secretory stimuli.

Several molecular forms of human GH (hGH) are present in blood, but their individual regulation is largely unknown. To examine the factors controlling the secretion of individual hGH variants, the relationship between the mixture of circulating hGH forms and the type of preceding secretory stimulus was studied in 18 normal subjects and 5 acromegalic patients. The stimuli employed were L-dopa, GH-releasing hormone-(1-40), exercise, spontaneous sleep-related and daytime secretory bursts, estrogens, and TRH in the acromegalic patients. Three monomeric hGH forms (22K, 20K, and acidic hGH) were identified in all samples; their mean relative proportions were 76.4%, 15.8%, and 7.9%, respectively. These proportions were similar in all subjects, regardless of stimulus, sex, or presence of acromegaly (P greater than 0.25). We conclude that the release of individual hGH forms is not stimulus specific, but, rather, that the secretory granule contents are released in toto upon somatotroph stimulation.

Big growth hormone forms in human plasma: immunochemical evidence for their pituitary origin.

Large molecular weight (oligomeric) forms of human growth hormone (hGH) are present in both pituitary extracts and plasma, but the origin of the plasma forms is not known. We used a monoclonal anti-hGH antibody (No. NA-71), previously employed to characterize hGH oligomers in pituitary extracts, to examine circulating hGH oligomers. This monoclonal antibody discriminated between monomeric and polymeric hGH forms in the pituitary. Plasma from normal subjects and acromegalic patients was fractionated by Sephadex G-100 chromatography and fractions were assayed by a monoclonal radioimmunoassay (RIA) using antibody NA-71 and by a polyclonal RIA. The oligomeric plasma hGH fraction showed decreased immunoreactivity in the monoclonal RIA, similar to that observed with pituitary oligomers. The immunopotency ratios of the various plasma hGH size isomers, as determined in the two RIAs, were virtually identical to those of pituitary hGH size isomers. We conclude that circulating hGH oligomers are immunochemically indistinguishable from pituitary hGH oligomers, and thus are most likely derived from pituitary stores.

A specific growth hormone-binding protein in human plasma: initial characterization.

Human (h) GH in plasma exists as a series of size isomers, which are in part explained by the presence of hGH oligomers. However, certain aspects of circulating large mol wt hGH, such as its high relative proportion compared to that in the pituitary, are poorly understood. To explore whether binding of hGH to plasma protein(s) could contribute to the phenomenon of large mol wt hGH, we incubated freshly prepared monomeric [125I]hGH or biosynthesized [3H]hGH with normal human plasma or serum at pH 7.4 for various time periods at 22 and 37 C. Plasma radioactive hGH patterns were then analyzed simultaneously with unincubated tracer hGH by Sephadex G-100 and G-200 chromatography. We found that part of the radioactivity was converted to a component with an apparent mol wt of 85,000, suggesting binding to a plasma protein(s). This phenomenon was inhibited in a dose-dependent fashion by unlabeled hGH. Saturation/Scatchard analysis indicated an association constant (Ka) of 2-3 X 10(8) M-1 and a maximum binding capacity of 20 ng hGH/ml plasma. Binding was rapid, reversible, and specific. A number of polypeptide hormones, including human placental lactogen, hPRL and rat GH, did not inhibit hGH binding. However, the 20K variant of hGH interacted weakly with the plasma binding component (Ka, 1.2 X 10(7) M-1; maximum binding capacity, 450 ng/ml). The binding component was heat labile and could be partially purified by gel permeation chromatography and affinity chromatography on a hGH-Sepharose column. Its estimated mol wt is 60,000-65,000, and it appears to bind one molecule of hGH to form a complex of 80,000-85,000 mol wt. The binding component is neither albumin nor an immunoglobulin. Under physiological conditions, a minimum of 15-18% of circulating hGH is presumably bound to this plasma component. We conclude that a specific, high affinity, low capacity binding protein for hGH with mol wt of 60,000-65,000 exists in normal and hypopituitary human plasma. hGH complexed with this protein forms part of big-big hGH. The biological significance of this binding protein remains to be investigated.

Slow metabolic clearance rate of the 20,000-dalton variant of human growth hormone: implications for biological activity.

The 20,000-dalton variant of human GH (hGH) (20 K) exhibits full growth-promoting bioactivity in the rat despite its poor interaction with GH receptors, as compared to the principal 22,000-dalton form of hGH (22 K). To test the possibility that prolonged survival time of 20 K in vivo may contribute to this apparent discrepancy, we compared the MCRs of 22 K and 20 K in the rat by the single injection technique. Both radiolabeled and native 22 K and 20 K were examined in this regard. The MCR of 20 K was 2- to 3-fold lower than that of 22 K, a statistically significant difference (P less than 0.05). The distribution volumes were similar for the two hGH forms and corresponded approximately to the extracellular fluid space. We conclude that the prolonged persistence of 20 K in the circulation may contribute to its higher than expected bioactivity in vivo in the rat.

Molecular forms of circulating growth hormone during spontaneous secretory episodes and in the basal state.

After pharmacological stimulation of the pituitary gland, human GH (hGH) in plasma consists of three or more monomeric molecular forms and several corresponding oligomers. However, the chemical nature of hGH circulating under physiological (stimulated or basal) conditions is not known. In particular, the molecular basis for the GH-like bioactivity of plasma is poorly understood. To gain information on the type(s) of hGH normally found in blood, we extracted hGH from plasma obtained at the time of spontaneous secretory episodes (nocturnal and random release) and during basal periods in 15 normal subjects. Appropriate plasma volumes (30 or 300 ml) were extracted by immunoadsorbent chromatography, and the extracts were analyzed by native polyacrylamide gel electrophoresis at pH 7.5 and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis at pH 10. The plasma hGH pattern at the time of spontaneous secretion was similar to that after pharmacological stimulation and consisted of 22K (principal), 20K, and acidic hGH as well as hGH dimer. In contrast, plasma hGH patterns during basal periods were highly variable and included immunoreactive hGH fragments in addition to the known hGH forms. Components with mol wt of 30K, 16K, and 12K were consistently identified. We conclude that 1) endogenously stimulated hGH secretion results in the same plasma hormone patterns as pharmacological stimuli; 2) several immunoreactive hGH fragments contribute to the heterogeneity of plasma hGH; and 3) hGH fragments may become a dominant part of total immunoreactivity in the basal state.

Plasma "big" and "big-big" growth hormone (GH) in man: an oligomeric series composed of structurally diverse GH monomers.

Human GH (hGH) immunoreactivity in plasma can be separated into three species of different molecular size by gel filtration (little, big, and big-big hGH). In contrast to pituitary high mol wt GH forms, the molecular nature of the big hGH forms in blood is not known. Therefore, we purified these hGH size isomers from the plasma of L-dopa-stimulated normal subjects and acromegalic patients. Plasma was chromatographed on Sephadex G-100, and fractions containing big-big, big, and little hGH were generated. hGH was extracted and concentrated from these fractions by immunoadsorbent chromatography and analyzed by polyacrylamide gel electrophoresis (PAGE), sodium dodecyl sulfate-PAGE, and isoelectric focusing. The resulting gel profiles indicated that the majority (70%) of big and big-big hGH was converted to little hGH during extraction and storage. The remainder migrated as distinct species with mol wt of approximately 45, 62, 80, and 110 K in sodium dodecyl sulfate-PAGE. These forms could be converted almost completely to little hGH by sulfhydryl reduction. Little hGH (both native and converted from big forms) was composed of several monomeric hGH species, namely the 22 K form (principal), the 20 K variant, and at least one acidic form. All hGH size isomers contained the same monomeric building blocks, although in somewhat different proportions. Big hGH, e.g. was particularly rich in 20K. No abnormal or previously unrecognized hGH forms were identified as components of big or big-big hGH. Binding of hGH to plasma proteins could not be demonstrated. We conclude that 1) plasma big and big-big hGH represent an oligomeric series composed of 22K (major), 20K, and one or more acidic hGH monomers, 2) the majority of these oligomers are noncovalently associated, with a smaller fraction consisting of monomers linked by disulfide bridges.

Circulating growth hormone forms after stimulation of pituitary secretion with growth hormone-releasing factor in man.

Human GH (hGH) in the circulation of acromegalic patients and pharmacologically stimulated normal subjects consists of several monomeric and oligomeric molecular forms. However, little is known about the nature of plasma hGH under physiological conditions. We examined the molecular composition of plasma hGH secreted in response to synthetic human pancreatic tumor GRF-(1-40) (hpGRF-40), a peptide closely resembling or identical to hypothalamic GRF. The peptide (10 micrograms/kg) was injected iv into six normal men, and blood was obtained 30 min later. Plasma hGH was characterized by gel filtration and by polyacrylamide gel electrophoresis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and isoelectric focusing after extraction from plasma by immunoadsorbent chromatography. At least 53% of hGH eluted as little (monomeric) hGH, 27% as big (dimeric) hGH, and 20% or less as big-big (oligomeric and spurious) hGH during gel filtration. Among the monomeric forms, the 22,000-dalton form was predominant (83%), with smaller quantities of the 20,000-dalton variant (11%), and one or more unidentified acidic forms (N alpha-acetylated, deamidated, or cleaved hGH) (6%) also present. The molecular composition of plasma hGH secreted in response to hpGRF-40 is similar to that released after pharmacological stimuli or that circulating in acromegaly.