Glucagon receptor binding, dissociation and degradation in rat liver plasma membranes studied by a microperifusion method.

The association process of glucagon receptor binding in purified rat liver plasma membranes and prolonged incubation of the hormone-receptor complex at 30 degrees C did not result in degradation of bound labelled glucagon. In contrast, up to 95% of the non-membrane-bound labelled glucagon was degraded. The rate of spontaneous dissociation of the glucagon-receptor complex was slow, and amounted to about 0.1% per min of that bound. GTP greatly enhanced the rate of dissociation. Half the maximal dissociation of the complex was effected by 10(-5) mol/l of GTP under equilibrium binding conditions. At maximally effective concentrations of GTP, 80% of the glucagon-receptor complex was dissociated within 2 min. A microperifusion system for the perifusion of isolated plasma membranes was devised and used for the separation of labelled glucagon from the plasma membranes subsequent to a GTP-induced dissociation of the hormone-receptor complex. Rebinding of the dissociated peptide to fresh membranes showed that maximum binding ability was retained. The glucagon molecule was protected against degradation while bound to the receptor, indicating that the glucagon effector system is completely separate from the inactivating system(s) in isolated plasma membranes. Thus, the hormonal effect of glucagon could be exerted through the sequential interaction of each glucagon molecule with several receptors.

New, simple insulin-receptor assay with universal application to solubilized insulin receptors and receptors in broken and intact cells.

A new, simple insulin-receptor-binding assay has been devised. The assay is based on the separation of free and receptor-bound 125I-labeled insulin in 80% ethanol. It was found that the insulin-receptor complex was fully stable at this ethanol concentration, regardless of the source of the receptor employed. The assay has been evaluated with solubilized insulin receptors and membrane-bound receptors from human placenta and porcine liver as well as intact cells with the IM-9 cell line. The assay is simple, rapid, and has large capacity. Comparisons of the ethanol-based assay to the conventionally employed assays with polyethylene glycol or microfuge centrifugation for the separation of free and bound 125I-insulin revealed large discrepancies between the assays. The ethanol-based assay always appeared to provide a better separation. Microfuge centrifugation of placental membranes precipitated approximately 3% of the ethanol-precipitable insulin-receptor complex, while polyethylene glycol precipitation of solubilized insulin receptors varied between 40 and 80% of the ethanol precipitability, depending on the receptor concentration employed.

Acute stress increases thyroid hormone levels in rat brain.

BACKGROUND: In experimental animals, exposure to uncontrollable stress induces a number of behavioral and biochemical changes that resemble symptoms seen in human depression and other psychiatric conditions. The present study used a yoked design to examine the effects of uncontrollable footshock stress on brain thyroid hormones in male and female rats. METHODS: Animals in one group received 15 trials where footshock could be terminated by pressing a lever (escapable shock). Rats in a second group received the same amount of shock, but had no control over shock termination (inescapable shock). Control rats received no shock. RESULTS: No significant differences were found among the three groups, for either males or females, in whole brain levels of thyroxine (T4) 3 hours after the footshock session. In contrast, significant group differences in brain levels of triiodothyronine (T3) were found for both males and females. In males, brain T3 was elevated by 21% in the inescapable shock group when compared to controls (p < .012). In females, brain T3 increased by 19% in the escapable shock group when compared to controls (p < .026). Plasma levels of both T3 and T4 were at control levels for all groups. CONCLUSIONS: These results provide the first demonstration that brain T3 levels change rapidly in response to acute stress. The data further suggest that the effects of stress controllability on brain T3 levels may be different for males and females.

Diuretic and clinical effects of low-dose furosemide in congestive heart failure patients.

A dose of 20 mg furosemide in congestive heart failure patients produces a significant diuretic and natriuretic effect. The peak effect was observed within 60-120 minutes in most patients. Twenty-four congestive heart failure patients were hospitalized for evaluation and management. Two withdrew from the study, and in three there was a prolonged (several months) remission of manifestations of congestive heart failure. The remaining 19 patients were treated with 40 mg furosemide per day for a four-week period. Six required 80 to 120 mg furosemide per day, and 13 were controlled on 40 mg per day. On 20 mg twice per day, one of the 13 patients dropped out voluntarily, two required a higher dose of furosemide, and 10 were controlled on this regimen for a four-week period. When dosage was reduced to 20 mg per day, five of the ten patients were controlled for an additional four weeks or longer, and five required higher doses of furosemide. Results of this study suggest that in congestive heart failure patients, 20 mg furosemide per day has significant diuretic and natriuretic properties. It also demonstrates that a number of patients with cardiac decompensation can be controlled on a relatively low dosage of furosemide and that periodic reevaluation of clinical status and diuretic requirements for maintenance therapy is of critical importance in management of patients with congestive heart failure.

Environmental effects on urinary volumes, biochemical constituents and their inter-relation.

This study has found low 24-h urine volumes in British expatriates in Saudi Arabia and suggests the possibility of urate stone formation in spite of the air-conditioned environment in which they were living. Urine volume was shown to be significantly correlated with calcium excretion in both sexes and to urate and sodium in males. Differences in 24-h urine concentrations of some but not all constituents between British-born subjects living in Britain and Saudi Arabia have been demonstrated.

A simple improved method for the measurement of cyclosporin by liquid-liquid extraction of whole blood and isocratic HPLC.

The current HPLC methods of cyclosporin measurement have been reviewed and all aspects assessed. A simple isocratic C-18 reverse phase HPLC method with improved efficiency is described for the routine measurement of cyclosporin in whole blood. An alkaline ether extraction is followed by an acid wash, solvent evaporation and two hexane washes of the reconstituted extract. The turn-round time for a single sample is 1 h. Daily batches of up to 40 patient samples can be easily measured with this method. The results are compared with those from the Sandoz radioimmunoassay (RIA) method.

The Middle East external quality assessment scheme for clinical chemistry.

The establishment and first 7 years' operation of an external quality assessment scheme for clinical chemistry in the Middle East region are described. The scheme utilises specimens distributed previously in the UK, and the performance of participating laboratories is assessed relative to the UK consensus values, taking account of method. Variance Index scoring has been used to quantitate performance, and there has been an improvement in average scores during the operation of the scheme. There are currently 88 participants, though some laboratories which failed to return results regularly were removed from the scheme. The consensus values from the scheme itself have now been validated, and in future the scheme should operate independently.

The Middle East External Quality Assessment Scheme for Clinical Chemistry: The first decade.

The Middle East External Quality Assessment Scheme for Clinical Chemistry has been operating for ten years, during which the number of participants has increased from 32 to 95 in 1990. The success of the Scheme in supporting better health care is reflected in the general improvement in performance of most laboratories. Initially linked to the United Kingdom National External Quality Assessment Scheme, it is anticipated that the Scheme will soon operate independently.

The effect of prolactin on cyclosporin in renal transplant patients.

The modulation of the immune response by interaction of prolactin and cyclosporin has been investigated in a total of 181 subjects, 121 males and 60 females. This study demonstrates a significant difference in the magnitude and fluctuation in prolactin and cyclosporin concentrations between males and females receiving cyclosporin as the single immunosuppressant. Levels of both analytes are lower in the male and show markedly less fluctuation than in the female. It is proposed that prolactin levels should be taken into account when determining the appropriate dosage regimen of cyclosporin in those patients receiving cyclosporin alone as immunosuppressant therapy.

Influence of timing in the fructosamine assay.

The fructosamine assay, based on the measurement of the reducing activity in serum at alkaline pH, provides an index of protein glycation. The reducing activity is expressed in equivalents of 1-deoxy-1-morpholinofructose (DMF) by direct comparison with the activity either of this synthetic compound or with a secondary protein standard calibrated against DMF. This study reports the influence of assay timing on the apparent serum fructosamine concentration. The kinetics of alkaline reducing activity in serum differed from that in both DMF and a secondary protein standard. When compared with DMF, activity in serum increased but decreased relative to the protein standard as the pre-incubation interval of the assay was shortened. The use of secondary protein standards results in underestimation of serum fructosamine concentrations when the pre-incubation phase of the assay is shorter than that used for the calibration of the secondary standard. Ascorbate exerted an inhibitory effect in fructosamine assays with pre-incubation times exceeding 5 min. The inhibition increased with both the concentration of ascorbate and the duration of the pre-incubation.

Serum fructosamine in diabetic pregnancy.

Serum fructosamine was measured in 275 blood donors, in 559 subjects with a normal pregnancy, in 32 gestational diabetics being treated with insulin and 69 being treated by diet only, and in 53 pregnant subjects with established diabetes. In none of the pregnant subgroups did the mean fructosamine concentration exceed that of the donor group. The concentration in normal pregnant subjects showed a modest but significant decrease with gestational age and an increase with maternal age. Hyperglycemic non-pregnant subjects (n = 24) had significantly increased serum fructosamine concentrations, and 96% of these subjects exceeded the upper 95% confidence limit for fructosamine in the donor group. A highly significant correlation was demonstrated between serum fructosamine and preprandial plasma glucose in the hyperglycemic subjects. A weak, but significant, correlation was shown for the entire population sample of antenatal patients, while this was non-significant within each of the sub-groups comprising established diabetics and gestational diabetics, respectively.

Bromocriptine suppression of TRH-stimulated prolactin and thyrotrophin release and accompanying inhibition of bromocriptine induced growth hormone release by TRH in normal man.

Six normal fasting males received on four separate occasions in random order (1) a placebo tablet followed 60 min later by 200 microgram of TRH intravenously (2) bromocriptine 2.5 mg orally followed by TRH intravenously (3) bromocriptine 2.5 mg orally followed by a placebo injection and (4) placebo tablet followed by placebo injection. Plasma prolactin and TSH responses to TRH were decreased following bromocriptine pretreatment. The rise of plasma growth hormone after bromocriptine was inhibited by TRH. The rise in plasma FSH seen after TRH injection was not influenced by bromocriptine pretreatment. Circulating LH and insulin concentrations were unaffected by any drug administration. These results suggest a dopaminergic influence on prolactin and TSH release in normal men, an inhibitory effect of TRH on bromocriptine stimulated growth hormone secretion, and no dopaminergic modulation of basal insulin secretion.

The prevalence of diabetes mellitus in male Saudi Arabs.

The prevalence of diabetes mellitus in 1385 males in the Al-Kharj area of Saudi Arabia was studied using the WHO criteria for screening and interpretation of glucose tolerance tests[1]. The prevalence was found to increase with age. No diabetic patients were found in the less than or equal to 24 year age group and only one (0.3%) in the age range: 25-34 years. There were seven (2.6%) in the age range: 35-44 years, 17 (9.6%) in the age range: 45-54 years, six (11%) in the age range: 55-64 years and three (23%) in the age range: greater than or equal to 65 years. The cases detected were relatively symptom free, but 65% of the diabetic patients were overweight.

Properdin factor B (Bf) polymorphism in Saudi Arabs. High frequency of a 'rare' allele BfS0.7.

The distribution of properdin factor B (Bf) phenotypes and the gene frequencies were investigated in 918 Saudi Arabs. A high frequency of the 'rare' allele BFS0.7 was observed BfS0.7 = 0.1514). The frequencies of the common Bf alleles (BfS = 0.5174, BfF = 0.3213) are outside the corresponding ranges of BfS, BfF gene frequencies found in European Caucasoids.

The Sunnybrook Gallstone Study: a double-blind controlled trial of chenodeoxycholic acid for gallstone dissolution.

The Sunnybrook Gallstone Study was a randomized, double-blind, controlled trial of chenodeoxycholic acid treatment over 2 years in 160 patients with radiolucent gallstones. Sixty-four patients received 750 mg daily, 53 received 375 mg daily and 43 received placebo. Total dissolution of gallstones occurred in 10.9% of patients on 750 mg daily, 13.2% of those on 375 mg daily and in no patient on placebo. The drug was tolerated well. Diarrhea severe enough to cause withdrawal from the study occurred in two patients. No patient developed clinically significant hepatotoxicity. Serum cholesterol rose 10% or more above baseline after 2 years in 33% of patients treated with chenodeoxycholic acid and in 30% of those on placebo. Cholecystectomy was performed in 10.9% of patients on 750 mg daily, 17% on 375 mg daily and 13.6% on placebo. Chenodeoxycholic acid given at these doses dissolved radiolucent gallstones safely but the efficacy was limited.