The effect of loop diuretics on the vestibular system. Assessment by recording the vestibular evoked response

Whether or to what extent loop diuretics, e.g., ethacrynic acid and furosemide, affect the vestibular system is controversial. We studied this problem by recording in cats the short-latency vestibular evoked response (VsER) to acceleration stimuli by skin electrodes before and after local or systemic administration of loop diuretics. The effect on the VsER was minimal in contrast to the major changes that appeared in the auditory evoked response, in which, among the waves known to originate from the brain stem, the most affected was N1. These findings suggest that the vestibular end-organ function is minimally affected by loop diuretics and that the changes in the vestibulo-ocular reflex reported by several authors might be due to the effect of the drugs on the central nervous system. Thus, recording of the VsER in experimental animal models might serve as a useful tool for direct evaluation of the effect of certain drugs and conditions on the vestibular system.

Direction-changing positional nystagmus: incidence and meaning

Direction-changing positional nystagmus (DCPN) is a nystagmus that changes its direction with different body and head positions. Many authors consider that it indicates the presence of a central nervous system lesion. Of 1,196 patients whose abnormal electronystagmographic (ENG) traces were reviewed, 46 (3.8 per cent) showed DCPN. Of these, ten (22 per cent) had central neurologic diseases, 14 (30 per cent) had peripheral vestibular diseases, and for 22 (48 per cent) there was no definite clinical diagnosis. Nineteen patients (41 per cent) with DCPN had ENG findings suggesting a peripheral vestibular lesion, while only five (11 per cent) had ENG findings suggesting a central vestibular lesion. Four of 44 control subjects exhibited DCPN. Thus, the presence of DCPN does not necessarily indicate disease of the vestibular system and definitely does not localize the site of a lesion in the vestibular pathways, but more often indicates a peripheral vestibular site. As with spontaneous nystagmus, lack of suppression with fixation suggests a central lesion.

Energy storage during DNA girase activity

In this work, we develop a minimal two-cycle model for the action of DNA girase. One of the cycles describes the ATP dependent chemicomechanical transduction performed by the enzyme. The other cycle describes the relaxing activity exhibited by girase on supercoiled DNA in the absence of substrates. Supercoiling of DNA is described as a random walk on a topological index. The mechanical energy storage in DNA is manifested in the fact that in general, the kinetic constants for the cycles do not satisfy Wegscheider relations. Finally, a connection is established between the degree of DNA supercoiling and the hydrolysis of ATP.

An unusual corneal complication of soft contact lens

An unusual complication caused by hydrophilic soft contact lenses developed in 13 patients (ten women and three men, 16 to 39 years old), most of whom had tight eyelids. The lesion consisted of an arc-like opacity in the superior cornea. The opacity lay in the superficial cornea about 1 to 3 mm from the corneoscleral limbus and had fine spokes extending away from the main trunk. In some cases the problem was unilateral and in others bilateral.

Exogenous ATP enhances calcium influx in intact thymocytes

Recent observations have indicated that exogenous adenosine triphosphate (ATP) may influence lymphocyte functions such as proliferation and cytoxicity. Here we report a novel activity of extracellular ATP--it specifically increases Ca2+ uptake in murine lymphocytes. ATP added to thymocytes increases the rate of [45Ca2+] uptake by up to 20-fold. The increased rate is seen with ATP concentrations as low as 500 microM and is half-maximal at approximately 2 mM ATP. The magnitude of stimulation by ATP is dependent on Mg2+ concentration, and ATP-Mg2+ complex is probably the true activator. Of the high-energy phosphate-containing compounds tested, including deoxy-ATP, only GTP showed a modest stimulation of calcium uptake. ADP, AMP, cyclic AMP, and adenosine did not significantly increase calcium uptake. Cellular integrity as indicated by trypan blue exclusion and ethidium bromide/acridine orange staining was unaffected by ATP. Ca2+ influx is the major mode of action of ATP in raising intrathymocyte Ca2+ levels, because neither the Ca2+ efflux nor the [45Ca2+]-Ca2+ exchange was significantly altered in the presence of ATP. Verapamil, a Ca2+ channel blocking agent, could not prevent the ATP effect, suggesting that ATP may be acting by a mechanism other than the voltage-dependent Ca2+ channel. An analysis of intracellular and extracellular ATP levels by chemiluminescence assay indicated no significant ATP entry into intact lymphocytes. Also, ATP added to the medium containing thymocytes was destroyed (approximately 50% by 20 min). The nonhydrolyzable ATP analogs, AMPPCP and AMPPNP, were unable to stimulate a significant amount of Ca2+ uptake, suggesting the involvement of a cell surface phosphotransferase activity. This was supported by the demonstration of a threefold to fivefold increase in the labeling of protein and phospholipid fractions obtained from intact thymocytes exposed to [gamma 32P]ATP for 30 min. Ca2+ is believed to play an important role in a variety of lymphocyte functions, including mitogenesis and natural killer cell activity. The data herein thus provide a potential mechanism for the action of exogenous ATP on these lymphocyte functions.

Histopathologic studies on transscleral argon-krypton photocoagulation with an exolaser probe

We performed argon and krypton laser photocoagulation of the retina and ciliary body on rabbit and monkey eyes using an exolaser probe. Clinically, transscleral retinal lesions produced a white circumscribed reaction. Histologically, we observed necrosis of the retina and choroid. Chronic lesions showed disorganization of the retina and formation of chorioretinal scars. Transciliary body laser coagulation damaged the ciliary body and its processes. The intraocular pressure was reduced in rabbits for one week and in monkeys for two weeks after 360 degrees transciliary laser coagulation. Scleral involvement was a common finding in transscleral laser coagulation.

Chemicomechanical transduction performed by enzymes activated by polymers

Kinetic models for the mode of action of processive and non-processive DNA-helicases are detailed. Fluxes at the steady state are analyzed, and the random walk of the enzymes on the DNA is studied in connection with the rate constants of the chemical reactions involved in the transformation of substrate to products. Finally, the constants of the kinetic model for the processive helicase are related to the parameters of an analogous viscoelastic model.

Preliminary observations on dissolution and bioavailability of triamterene-hydrochlorothiazide combination products

The dissolution profiles of two brands of triamterene-hydrochlorothiazide (TRM-HCT) combination tablets and two brands of TRM-HCT combination capsules were studied using the USP paddle method at 100 rev min-1 in acid medium (0.1N). The tablets represent two products marketed in Germany, whereas the capsules represent the approved innovator's product and an unapproved generic product. The tablets dissolved almost 100 per cent in 15 min whereas the capsules dissolved less than 25 per cent in 60 min. A pilot bioavailability study was carried out in four normal healthy male volunteers. Urine samples were collected over a 48 h period and analysed for TRM, its major metabolite TRM-sulfate, and HCT using HPLC methods. The dissolution characteristics of TRM can be associated with the total drug excretion (absorption) of the product. On the other hand, the excretion (absorption) of HCT was independent of dissolution characteristics of the products. However, in TRM-HCT combination product, there appears to be a 50 per cent reduction in HCT excretion (absorption) when compared to the reported excretion (absorption) from a marketed single-entity product.

Inaccuracy of angiography in the diagnosis of carotid ulceration

It is generally stated that ulceration of the carotid bifurcation plaque may give rise to embolization and symptoms of cerebral ischemia. It has been suggested that prophylactic carotid endarterectomy is indicated in asymptomatic patients if the angiogram is interpreted as showing ulceration. We therefore determined the accuracy of the radiologic diagnosis of ulceration by comparing the radiologic and morphologic findings in 155 carotid endarterectomies. Ulceration was diagnosed in 54% of the angiograms and 47% of the surgical specimens and was not related to the degree of stenosis. Angiography had a sensitivity of 73%, a specificity of 62% and an overall accuracy of 67%. For the non-flow-restrictive lesions these figures were 65%, 66%, and 66%. If surgery were based on the angiographic diagnosis of ulceration in plaques with less than 50% stenosis, 16 out of 42 operations (38%) would have been done unnecessarily. Variability of the angiographic diagnosis of ulceration is also shown by a high interobserver variability; two sets of two authors read the angiograms independently and disagreed in 24% of the cases. The decision to operate should not depend entirely upon the angiographic diagnosis of ulceration.

Prolymphocytic leukemia: postmortem findings after long-term survival

A patient had prolymphocytic leukemia and survived for 44 months. A partial remission for more than 11 months and a short complete remission were induced by agents commonly used for the treatment of acute myelocytic leukemia. However, surface markers identified the disease as of B-cell origin.

Lectin- and ionophore-stimulated Ca2+ influx in murine lymphocytes: inhibition by disialoganglioside

Gangliosides suppress lymphocyte mitogenesis when added exogenously to the cells. On the premise that the mechanism of ganglioside action may be an interference with primary induction events, mitogen-induced 45Ca2+ influx in murine lymphocytes was studied. Disialoganglioside (GD1a) at physiopathological concentrations inhibits concanavalin A-induced 45Ca2+ uptake as well as blast transformation. The suppressive action of GD1a is both concentration dependent (50% suppression at 13 microM) and very rapid (within 1 min). GD1a is not cytotoxic nor does it significantly alter the rate of Ca2+ efflux. The uptake studies were extended to A23187, a compound with mitogenic and specific divalent cation ionophore activities. Ca2+ uptake by lymphoid cells from AKR/J, Swiss, and CBA mice is stimulated by A23187; and GD1a, in a dose-dependent manner, inhibits the ionophore-induced 45Ca2+ influx. Pretreatment of thymocytes with GD1a renders the cells greatly insensitive to the subsequent ionophore activity of A23187. The results suggest that exogenous gangliosides may function as an inhibitor of some of the mitogen-triggered early events, including Ca2+ metabolism, and thus influence the immunological behavior of intact lymphoid cells.