Search PubMed⌕ Search

Biomedical subjects

D H Robinson

Publications and source records attributed to D H Robinson.

49 records · Page 3Linked to original sources
PubMed1987

Ouabain binding in tadpole ventral skin. I. Kinetics and effect on intracellular ions.

The short-circuit current across tadpole skin is inhibited by only 50% after 2 h of exposure to 10(-2) M ouabain [Am. J. Physiol. 237 (Regulatory Integrative Comp. Physiol. 6): R74-R79, 1979]. To determine the Na pump sensitivity to ouabain, the kinetics of ouabain binding in tadpole epidermis and the effect of ouabain on intracellular Na and K were tested. In tadpole epidermis a high-affinity dissociation constant (KD) for ouabain of 1.21 +/- 0.20 X 10(-7) M was found, which is similar to the KD in frog skin (1.27 +/- 0.16 X 10(-7) M). Incubation of tadpole epidermis in ouabain for 1 h increased intracellular Na concentration from 48.8 +/- 3.3 to 66.2 +/- 4.9 mM (P less than 0.005) and decreased K concentration from 115 +/- 7 to 104 +/- 9 mM (P less than 0.01). Two hours of ouabain exposure increased intracellular Na concentration from 41.4 +/- 2.4 to 73.3 +/- 4.3 mM (P less than 0.0005) and decreased K concentration from 113 +/- 10 to 85.9 +/- 5.3 mM (P less than 0.05). Regression analysis of the change in Na and K concentrations reveals a slope of 14.7 +/- 2.5 mM/h for the Na gain, which is similar in magnitude to the rate of K decrease (-13.8 +/- 4.7 mM/h). It is hypothesized that the residual short-circuit current seen in tadpole skin after ouabain exposure is a result of current being carried through the tissue by a slow gain of Na across the apical membrane and an equivalent loss of K across the basolateral membrane.

Animals↗
PubMed1987

Ouabain binding in tadpole ventral skin. II. Localization of Na pump sites.

By use of [3H]ouabain autoradiography, the distribution of ouabain binding sites in the tadpole ventral skin and the change in the pattern of binding during metamorphosis were examined. In the tadpole the greatest grain density, and hence density of Na pumps, was found in the outer one-third of the epidermis. The pattern of binding changed at (Anat. Rec. 94: 7-23, 1946) stage 20 to a homogenous distribution. At stage 21 the highest grain density was in the middle third of the epidermis. The adultlike pattern of binding, with the highest density in the serosal two-thirds of the epidermis, was noted at stages 22 and 23. The average grain density through the entire tissue is approximately 2.4-fold higher in the stage 23 animal than in the tadpole with the significant increase in density occurring between stages 20 and 21. Since the adult Na transport characteristics are also not fully developed until stage 22 (Biochim. Biophys. Acta 692: 455-461, 1982), it is proposed that the development of the Na-pump characteristics is coincident with the development of other adult transport properties.

Age Factors↗
PubMed1984

Comparison of body fluid compartment sizes in Brattleboro homozygous and Long-Evans rats.

Because of their hypothalamic diabetes insipidus (DI), Brattleboro homozygous rats exhibit profound polyuria and polydipsia with elevated plasma osmolalities. This combination of symptoms has led to the tacit assumption that these animals are chronically volume contracted. However, the few direct measurements that have been published indicate otherwise. In the present study, total body water (TBW), total body lipid content, and plasma volume were measured in conscious DI rats and compared with corresponding values in weight-matched conscious Long-Evans (LE) rats. Fat content of DI rats (5.0 +/- 0.4 g/100 g body wt) was significantly lower than that of LE rats (7.6 +/- 0.6, P less than 0.005). TBW was not significantly different between the two strains whether expressed as milliliters per 100 g wet wt (DI 69.2 +/- 0.4 vs. LE 67.7 +/- 0.7) or as milliliters per 100 g fat-free wet wt (DI 73.4 +/- 0.5 vs. LE 73.3 +/- 0.4). Plasma volume of DI rats (4.4 +/- 0.1 ml/100 g body wt) was significantly higher than that of LE rats (3.9 +/- 0.2, P less than 0.025). Extracellular fluid volume was similar in the two strains although, for this measurement, the animals were neither weight- nor age-matched. Accordingly, the data indicate that under the conditions of this study the DI rat is not chronically volume contracted. It would appear that, given an adequate water supply, water balance can be achieved via the thirst mechanism, perhaps abetted by vasopressin-independent mechanisms of urine concentration.

Adipose Tissue↗
PubMed1984

A micromethod for long-term in vitro culture of bone marrow cells.

A micromethod to study long-term culture of bone marrow cells in vitro has been developed. Using Linbro wells one-fourteenth of the cells and medium usually required for culture in a flask are plated. Thus 40-50 cultures from a single mouse can be studied at any one time. Adherent-layer formation and supernatant cell recovery were very similar when Linbro -well cultures were compared with standard large-flask cultures. In the microculture system, supernatant and adherent-layer cell numbers increased following medium change reaching a maximum 3-4 days later and decreasing by day 7. Supernatant cells were in equilibrium with those of the adherent layer as cell numbers in both compartments prior to and following medium change fluctuated identically. Following medium change, a significant increase in myeloblasts occurred at 24 h and promyelocytes and myelocytes increased 48-72 h later. In contrast no discernible pattern in daily CFU-C production was detected. These findings provide insight into the cellular kinetics of long-term marrow culture and highlight the usefulness of this method to study hematopoiesis at frequent intervals.

Animals↗
PubMedDate not supplied

Controlled release captopril microcapsules: effect of non-ionic surfactants on release from ethyl cellulose microcapsules.

Captopril microcapsules were prepared with different viscosity grades of ethyl cellulose by temperature induced coacervation from cyclohexane. Both non-ionic surfactants or their combinations and 2 per cent absolute alcohol as cosolvent were added to the coacervation system to ensure complete solvation of the ethyl cellulose and efficient microencapsulation of the drug. The in vitro dissolution was studied in 0.1 N hydrochloric acid. Microcapsules prepared using 2 per cent Tween 80 with ethyl cellulose of 41 c.p. viscosity grade exhibited the most prolonged release with a t70 per cent of 55 min in comparison to 7.75 min for control microcapsules prepared without surfactant. Different kinetic models have been used to explain the release. The best fit with the highest correlation coefficients was the first-order kinetics plot with two straight lines having two different slopes. The initial slope presents the faster release rate than the terminal slope. This fast release would be useful for the initial dose of the prolonged release formulation.

Capsules↗
PubMedDate not supplied

Controlled release captopril microcapsules: effect of ethyl cellulose viscosity grade on the in vitro dissolution from microcapsules and tableted microcapsules.

Captopril microcapsules were prepared using four different viscosity grades of ethyl cellulose (core: wall ratios 1:1, 1:2 and 1:3) by temperature induced coacervation from cyclohexane. In vitro dissolution studies in 0.1 M hydrochloric acid showed that the drug release was dependent on the core to wall ratio, the viscosity grade of the ethyl cellulose and thus the total viscosity of the coacervation system. Viscosity grade of greater than 100 c.p. was unsuitable for microencapsulation by coacervation method at the concentration used. The surface characteristics of a 1:2 core to wall ratio were studied by scanning electron microscopy. The surface of the microcapsules prepared with 10 c.p. viscosity grade was comparatively more porous with larger size pores than 50 c.p. viscosity grade of ethyl cellulose. However, 300 c.p. viscosity grade showed incomplete wall formation. The microcapsules did not fragment during dissolution, alter in shape or size, or show evidence of enlargement of the surface pores. The tensile strength of tablets prepared at constant pressure from each batch of microcapsules (mean diameter 675 microns) increased as both the core to wall ratios and the viscosity of ethyl cellulose increased. The dissolution rate of the drug from tableted microcapsules was significantly delayed. The in vitro release gave best correlation with first order release kinetics when compared to zero-order and square-root-of-time equations.

Capsules↗
PubMedDate not supplied

Embolization of meningohypophyseal and inferolateral branches of the cavernous internal carotid artery.

BACKGROUND AND PURPOSE: Despite the continued improvements in endovascular techniques this decade, few dedicated studies addressing the feasibility of such procedures or their efficacy relative to risk have been conducted. The purpose of this study was to use current endovascular techniques to assess the feasibility, effectiveness, and safety of direct selective catheterization and embolization of the small branches of the cavernous segment of the internal carotid artery. METHODS: We retrospectively reviewed the findings in 10 patients with lesions (five meningiomas and five arteriovenous malformations) primarily or partly supplied by branches of the meningohypophyseal trunk or inferolateral trunk who had undergone endovascular embolization of the feeding arteries during the period from 1991 to 1997. In each case, the artery was selectively catheterized with a microcatheter/microguidewire system and embolized with polyvinyl alcohol particles (n = 5), n-butyl cyanoacrylate tissue adhesive (n = 4), or both (n = 1). RESULTS: In all 10 patients, the feeding artery from the meningohypophyseal trunk (eight patients) or inferolateral trunk (three patients; one patient with both) was successfully catheterized and embolized. In nine patients, embolization resulted in complete obliteration of the vascular territory; in the remaining patient, blood supply was decreased by an estimated 80%. No immediate or delayed complications occurred. CONCLUSION: Advances in microcatheter and microguidewire technology allow more efficient and safer selective catheterization and embolization of branches of the cavernous segment of the internal carotid artery than in the recent past. Meticulous technique and detailed knowledge of the vascular anatomy of the cavernous sinus region are necessary to maximize lesion devascularization and to minimize the risk of stroke, cranial nerve palsies, and blindness.

Adult↗