Search PubMed⌕ Search

Biomedical subjects

K Kern

Publications and source records attributed to K Kern.

88 records · Page 5Linked to original sources
PubMed1985

Reversible inhibitors of beta-glucosidase.

A variety of reversible inhibitors of sweet almond beta-glucosidase were examined. These included simple sugars and sugar derivatives, amines and phenols. With respect to the sugar inhibitors and, indeed, the various glycoside substrates, the enzyme has what can be considered a "relaxed specificity". No single substituent on glucose, for example, is essential for binding. Replacement of a hydroxyl group with an anionic substituent reduces the affinity while substitution with a cationic (amine) substituent enhances the affinity. Amines, in general, are good inhibitors, binding more tightly than the corresponding alcohols: pKiRNH3+ = 0.645pKiROH + 1.77 (n = 9, r = 0.97). The affinity of a series of 10 primary amines was found to be strongly influenced by substituent hydrophobicity: pKi = 0.52 pi + 1.32 (r = 0.95). The major binding determinant of the glycoside substrates is the aglycon moiety. Thus, the Ki values of phenols are similar in magnitude to the Ks values of the corresponding aryl beta-glucoside. The pH dependence for the inhibition by various phenols indicates that it is the un-ionized phenol which binds to the enzyme when an enzymic group of pKa = 6.8 (+/- 0.1) is protonated. The affinity of the phenol inhibitor is dependent on its basicity with a Brønsted coefficient for binding of beta = -0.26 (n = 14, r = 0.98). The pH dependence of the binding of two particularly potent beta-glucosidase inhibitors was also examined. 1-Deoxynojirimycin (1,5-dideoxy-1,5-imino-D-glucitol) has a pH-corrected Ki = 6.5 microM, and D-glucono-1,5-lactam has a pH-corrected Ki = 29 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucosidases↗
PubMed1984

The effects of alpha 2-adrenergic and serotonergic receptor antagonists on cyclic blood flow alterations in stenosed canine coronary arteries.

Platelets possess alpha 2-adrenergic and serotonergic (5-hydroxytryptamine) receptors which are thought to mediate the in vitro proaggregatory effects of epinephrine and serotonin, respectively. However, their importance in platelet aggregation in vivo is uncertain. In the present study, we evaluate the ability of yohimbine and ketanserin, relatively selective alpha 2-adrenergic and serotonin antagonists, respectively, to alter cyclic flow reductions in stenosed coronary arteries in open-chest, anesthetized dogs. These cyclic flow reductions, characterized by progressive declines in coronary blood flow interrupted by abrupt and, often spontaneous, restorations of flow, were produced by cylindrical constrictors placed on the left anterior descending coronary artery. A pulsed Doppler flow probe, placed proximal to the constrictor, was used to measure coronary blood flow. Regional myocardial blood flow was measured with 15-micron radiolabeled microspheres before coronary constriction and when coronary blood flow appeared to be at its nadir and zenith during cyclic flow reductions. After the cyclic flow reductions had been observed for 1 hour, yohimbine (1-2 mg/kg), ketanserin (0.25 or 0.5 mg/kg), or saline was given, and coronary blood flow and hemodynamics were monitored for another hour. The frequency of cyclic flow reductions and the mean of the three lowest nadirs of coronary blood flow (mean +/- SE) were compared between the first and second hours. Ketanserin, at doses of 0.25 and 0.50 mg/kg, virtually abolished cyclic flow reductions in all dogs tested. Yohimbine [1 mg/kg ( n = 14)] was partially effective in reducing the frequency (9.6 vs. 5.5 cyclic flow reductions/hr) and severity of cyclic flow reductions (nadirs of coronary blood flow = 6.2 +/- 2.4 vs. 20.9 +/- 6.1% of control). A higher dose of yohimbine [2 mg/kg (n = 7)] was no more effective. The frequency (9.3 +/- 0.9 vs. 9.3 +/- 1.0 CFR/hr) and severity (17.4 +/- 5.4 vs. 12.4 +/- 3.9% of control coronary blood flow) of cyclic flow reductions were not changed by saline. The relatively selective alpha 1-adrenergic antagonist, prazosin (0.01 mg/kg, iv), and the beta-adrenergic antagonist, propranolol (1-2 mg/kg, iv), did not affect the frequency or severity of cyclic flow reductions. Thus, the abilities of yohimbine to inhibit and ketanserin to abolish cyclic flow reductions in stenosed canine coronary arteries suggest that serotonin and, possibly, alpha 2-adrenergic agonists may influence cyclic flow alterations importantly in this model.

Adenosine Diphosphate↗
PubMedDate not supplied

Some aspects of doctor-patient relationships and the older patient.

A study of doctor-patient relationships concerning older patients was carried out among general practitioners in German-speaking Switzerland. Information was sought by questionnaire on general practitioners' personal characteristics and characteristics of practice (independent variables), on attitudes and personality characteristics (intervening variables), and on consultation behavior (dependent variables). Findings indicated the effects of personal background factors, of personality characteristics, and of attitudes on consulting behavior of general practitioners vis-à-vis the elderly. A causal path analysis was carried out and showed that general practitioners' age (and what age stands for in terms of life events) and, to a lesser extent, proportion of elderly in the practice were important causal determinants in general practitioners' consulting behavior vis-à-vis the elderly. Other variables were also found to be significant as causal links; these included preventive orientation, attitude to the aged, extraversion, and conservatism. In conclusion, some practical implications are briefly discussed.

Adult↗