Assessment of experts' approach to insulin therapy and development of a simulator for diabetes insulin adjustment.

OBJECTIVE: To develop a computer program (Macintosh) to predict changes in blood glucose after changes in insulin dose, timing, and regimen. RESEARCH DESIGN AND METHODS: We established program parameters (apparent insulin action profiles; different for insulin-dependent and non-insulin-dependent diabetes mellitus) to match predictions by five diabetes specialists at our hospital of blood glucose changes after insulin-dose adjustment in 22 hypothetical patient cases. We compared the action profiles, which represent the blood glucose changes predicted by the experts with glucose-clamp studies of insulin action. We tested the program's performance in 22 different hypothetical cases against the responses of 15 specialists from outside our hospital. RESULTS: The specialists, when predicting effects of insulin dose adjustment, integrate numerous processes (insulin action, diet, sequential blood glucose interactions). They could not specify algorithms for determining these individual factors, but they could easily predict the overall effect in the context of patient cases. The computer program's insulin-action profiles simulate this "composite" approach. The developed program incorporates multiple insulin regimens, which may be changed during the stimulation, and adjusts predicted responses according to the patient's estimated sensitivity to insulin. Its predicted change in 172 blood glucose levels (22 cases) correlated well with the corresponding means of the outside specialists (r = 0.83, P = 0.0001). Comparing this correlation with that of individual specialists ranked the program third. CONCLUSIONS: A computer program can simulate specialists' "composite" approach (not based purely on conscious application of physiological data) to insulin adjustment.

Human somatic mutation assays as biomarkers of carcinogenesis.

This paper describes four assays that detect somatic gene mutations in humans: the hypoxanthine-guanine phosphoribosyl transferase assay, the glycophorin A assay, the HLA-A assay, and the sickle cell hemoglobin assay. Somatic gene mutation can be considered a biomarker of carcinogenesis, and assays for somatic mutation may assist epidemiologists in studies that attempt to identify factors associated with increased risks of cancer. Practical aspects of the use of these assays are discussed.

Identification of the major sources of error in estrogen receptor measurements for individual laboratories using both tissue and cytosol samples.

The major sources of error between laboratories performing estrogen receptor measurements in tissue samples were identified for 17 participating laboratories in a trial conducted by the Australasian Quality Assurance programme. Both tissue and cytosol samples were provided, and the In-House assays were compared with the ER-EIA kit (Abbott Laboratories, U.S.A.) as a reference assay. For both the In-House and Abbott assays, tissue samples resulted in a between laboratory CV of about 55% and a within laboratory CV of about 30%. In contrast to tissue samples, the between laboratory CV for cytosol samples was reduced to 41% for the In-House assays and to 33% for the Abbott assay, whereas the within laboratory CV was reduced to 10% for both types of assay. The different methods of tissue homogenization by themselves were not found to be sources of error, and protein extraction efficiency from tissue was strongly correlated with protein measurement (P less than 0.0005). The major sources of error due to protein measurement, cytosol preparation, In-House and Abbott assays were evaluated for individual laboratories. The results indicated absence of any major sources of error for four laboratories, while one, two and three or more sources were indicated for seven, three and three laboratories respectively. The conclusion that about half the participants need to improve their ER assays was confirmed by three independent reviews. Furthermore, the trial demonstrated that tissue samples are essential as quality assurance material for a realistic assessment of ER assays in biopsy specimens.

Sources of improvement in between laboratory variation in estrogen and progestin receptor measurement using tissue samples during the Australian Quality Assurance Programme.

Tissue and cytosol samples were compared as quality control material for assessment of between and within laboratory error in measurement of estrogen and progestin receptors (ER and PR) in a series of four trials for a total of 17 participating laboratories during the Australasian Quality Assurance Programme. For tissue samples, a substantial reduction in between laboratory CVs for both ER and PR from about 90 to 50% was achieved during the programme. In contrast, for cytosol samples a substantially lower between laboratory CV of about 30% was obtained. Tissue sample heterogeneity could be excluded as a major source of variation between laboratories. The likely source of the observed improvement in CV for tissue samples during the trials was due to a reduction of the initial under-estimation of receptor concentration in tissue samples by some of the participants. Although cytosol preparation from tissue samples was shown to be one major source of error, other sources of error such as the receptor assay itself and the associated protein measurements were identified. It is concluded that fragmented tissue samples are essential for a realistic assessment of between laboratory error in receptor measurements in biopsy material such as obtained from clinical breast cancer samples.

Error in laboratory reference limits as shown in a collaborative quality-assurance program.

Laboratories participate in collaborative quality-assurance programs to maintain and improve the quality of their diagnostic assays, but little attention has been paid to diagnostic quality in these programs. We used a national quality-assurance program to assess the quality of laboratory reference intervals as exemplified by triiodothyronine, thyroxin, and thyrotropin immunoassays. The limits of the reference intervals used by laboratories bear virtually no relationship to laboratory bias, i.e., whether assays read "high" or "low." Further, correcting assay results from different laboratories for the reference limits used increases rather than decreases interlaboratory scatter. We conclude that the analytical quality of immunoassays now exceeds the quality of the reference limits supplied to clinicians to assist diagnosis, and that nationally or internationally defined reference limits would therefore provide more information at less cost than do individual laboratory reference limits.

Tolbutamide increases hypothalamic serotonin activity in the rat.

Sulfonylureas are potent hypoglycemic agents; however, their mechanism of action remains incompletely understood. Recent data indicate that hypothalamic norepinephrine (NE) plays a major role in mediating the central neural regulation of blood glucose. We therefore examined whether the sulfonylurea tolbutamide might lower serum glucose via an effect on hypothalamic NE neuronal activity, and compared the effects with those of 2-deoxyglucose-induced neuroglycopenia and of chronic insulin administration. Serum glucose levels fell and serum insulin levels rose 10, 20, and 30 min after acute tolbutamide injection. Serum glucose concentrations were reduced after chronic tolbutamide administered in drinking water, but serum insulin did not change. Hypothalamic NE neuronal activity was increased 10 min after tolbutamide administration, but not at the later times, nor during chronic tolbutamide administration. However, consistent with a rise in serotonin (5-HT) neuronal activity, hypothalamic 5-hydroxyindoleacetic acid (5-HIAA) and the 5-HIAA/5-HT ratio rose 30 min after acute tolbutamide and during chronic tolbutamide administration. This rise was not due to neuroglycopenia per se, since hypothalamic NE neuronal activity was increased and hypothalamic 5-HT neuronal activity was reduced after 2-deoxyglucose-induced neuroglycopenia. Furthermore, the effect of chronic tolbutamide contrasted with that of chronic insulin administration where hypothalamic NE neuronal activity was increased, while hypothalamic 5-HT neuronal activity was unchanged. We conclude that tolbutamide does not lower serum glucose via a direct effect on hypothalamic NE neuronal activity; however, we note that tolbutamide specifically increases hypothalamic 5-HT neuronal activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term bromocriptine therapy may restore the inhibitory control of prolactin release in some patients with pathological hyperprolactinemia.

While bromocriptine is effective in controlling hyperprolactinemia, it is not known if bromocriptine therapy can restore the abnormal regulation of prolactin (PRL) release found in patients with pathological hyperprolactinemia. We report 15 hyperprolactinemic patients treated for a mean duration of 5.5 +/- 0.6 years (mean +/- SE) in whom stimulation tests to assess PRL control mechanisms [thyrotropin releasing hormone (TRH) and metoclopramide] were performed before and at least one month after withdrawal of bromocriptine therapy. The basal PRL level after withdrawal of bromocriptine therapy was significantly lower (p less than 0.001) than that before therapy. All patients had blunted PRL stimulatory responses to TRH and metoclopramide (% delta 16.0 +/- 5.6%) before treatment. After withdrawal of bromocriptine, PRL responses to stimulatory tests were significantly improved in seven patients (termed 'responders', % delta 376 +/- 55%) but remained unchanged in eight patients (termed 'non-responders', % delta 9.2 +/- 3.0%). Basal PRL levels were significantly lower (p less than 0.01) in responders (290 +/- 35 mIU/l) than in non-responders (10360 +/- 6790 mIU/l). Four of the responders have maintained normoprolactinemia and normal stimulated PRL responses for 15 months to three years following cessation of bromocriptine therapy and appear to be in remission. Favourable factors amongst the responders were the female sex, absence of a macroadenoma, and a pre-treatment PRL level below 3000 mlU/l. PRL stimulation tests performed before therapy could not predict which patients would respond. No relationship was found between duration of therapy, or age at presentation, and improvement after bromocriptine.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationships between brain noradrenergic activity and blood glucose.

Glucose is the principal energy substrate for the brain and studies have shown that the brain is able to increase glucose availability in the face of glucose starvation (neuroglycopaenia). The mechanisms, believed to be hypothalamic, that may be involved in a brain/blood glucose control system have not yet been identified. We have used novel techniques for assessing brain monoamine neuronal activity to investigate its relationship to blood glucose concentrations in the rat. We describe here two important relationships which emerge from these studies. One is that activation of hypothalamic noradrenaline (NA) activity following stress is associated with concurrent increases in plasma glucose concentrations. This relationship is linear and independent of the adrenal or pituitary glands. The second is an inverse relationship between plasma glucose concentration and hypothalamic NA neuronal activity--high blood glucose levels significantly inhibited the hypothalamic NA activity responses to stress, alpha 2-adrenergic blockade and adrenalectomy. Thus glucose (or a metabolite of it) seems to provide a negative feedback signal sensed by hypothalamic NA neuronal systems which, in turn, appear to stimulate liver glucose output by a neural mechanism.

The stimulation of human prolactin secretion by 3-Iodo-L-tyrosine.

Oral administration of a single 1 g dose of MIT to 10 normal male and female subjects resulted in a rise in serum prolactin in each subject. The mean peak level of serum prolactin attained by the 10 subjects was 36.3 plus or minus 7.9 ng/ml which was highly significantly elevated (P smaller than 0.0005) above the mean basal level of 5.3 plus or minus 1.0 ng/ml. While there was no significant difference between the basal serum prolactin levels of male and female subjects, the mean peak level attained by male subjects following MIT (18.8 plus or minus 3.3 ng/ml) was significantly less (P smaller than 0.0025) than that recorded for the female group (62.5 plus or minus 9.1). Serum levels of growth hormone (GH), thyroid-stimulating hormone (TSH), luteinizing hormone (LH), triiodothyronine (T3), thyroxine (T4) and cortisol were not significantly altered following MIT administration. The complete absence of side effects due to MIT make it a suitable drug for the acute clinical assessment of pituitary prolactin reserve.