Search PubMed⌕ Search

Biomedical subjects

R N Pittman

Publications and source records attributed to R N Pittman.

At least 91 records · Page 5Linked to original sources
PubMed1986

Genetic influence on the regulation of beta adrenergic receptors in mice.

The regulation of beta adrenergic receptors was investigated in inbred mouse strains in which previous studies revealed differences in the regulation of dopamine receptors. The density of beta adrenergic receptors in the cerebral cortex of BALB/J mice was about one-third of that in CBA/J and C57BL/6J mice. Strain differences in the binding of [125I]iodohydroxypindolol to beta adrenergic receptors were due to changes in the density of beta-1 adrenergic receptors. Chronic administration of propranolol did not result in an increase in the density of beta adrenergic receptors receptors in cortices of C57BL/6J and BALB/cJ mice were observed. In contrast, pretreatment with 6-hydroxydopamine resulted in increases in the density of beta adrenergic receptors in the cerebral cortex of all three strains. Analysis of the effects of these treatments on the subtypes of beta adrenergic receptors revealed that the changes were restricted to changes in the density of beta-1 receptors. The failure to observe a response to propranolol in CBA/J mice expands the extent of deficits reported previously in this strain for striatal dopamine receptor supersensitivity after chronic treatment with haloperidol (Severson et al., Brain Res. 210: 201-215, 1981). CBA/J mice may be a useful model for genetic analysis of mechanisms for the control of receptor sensitivity and to investigate the impairments of the regulation of catecholaminergic receptors observed in aged rodents.

Age Factors↗
PubMed1985

Release of plasminogen activator and a calcium-dependent metalloprotease from cultured sympathetic and sensory neurons.

Cultures of neurons from neonatal rat superior cervical, dorsal root, and trigeminal ganglia were grown in the absence of nonneuronal cells in serum-free defined medium. Proteins metabolically labeled with radioactive amino acids and spontaneously released into the culture medium were studied using two-dimensional gel electrophoresis and photofluorography. All three populations of neurons released 12-15 major proteins into the culture medium. Four proteins were released selectively by sympathetic neurons and two proteins were consistently released by both populations of sensory neurons but not by sympathetic neurons. Enzymatic activities are associated with at least two of the released proteins. One is a calcium-dependent metalloprotease, and the other a plasminogen activator. The calcium-dependent metalloprotease has a MW of 62 kDa, requires millimolar calcium for maximum activity, and has a restricted substrate specificity. It degraded native and denatured collagen more readily than casein, albumin, or fibronectin and denatured collagen (gelatin) was a better substrate than native collagen. The plasminogen activator released by neurons has a MW of 51 kDa and is converted to an active 32 kDa form. Its physiochemical properties are similar to urokinase and it was precipitated by a rabbit antiserum produced against human urokinase. A large fraction of both proteases was released by distal processes and/or growth cones suggesting that these proteases could be involved in growth cone functions.

Animals↗
PubMed1984

Desensitization of beta-adrenergic receptor-coupled adenylate cyclase activity. Differences following exposure of cells to two full agonists.

The effects on the beta-adrenergic receptors of intact L6 muscle cells of exposure to agonists were investigated. Treatment of cells with isoproterenol decreased GTP-, isoproterenol-, and zinterol-stimulated adenylate cyclase activities, whereas exposure of cells to zinterol decreased only isoproterenol- and zinterol-stimulated activities. Although the effects of these two full agonists on GTP-stimulated adenylate cyclase activity were different, the time courses for development and reversal of the effects were similar. The decrease in agonist-stimulated adenylate cyclase activity observed in membranes prepared from cells previously exposed to isoproterenol or zinterol was due to both an increase in the concentration of agonist required for half-maximal activation and a decrease in the maximum level of activation. No effects on fluoride- or manganese-stimulated activities were observed following exposure of cells to either agonist. Decreases in GTP-stimulated adenylate cyclase activity were also observed following exposure of cells to epinephrine, Cc-25, fenoterol, norepinephrine, terbutaline, or metaproterenol, but not following incubation of cells with dobutamine or salmefamol. The results suggest that full agonists interacting with the same receptor can induce different changes in the components of the adenylate cyclase system. Desensitization following exposure to zinterol may result from modification of the receptor, whereas that following exposure to isoproterenol may be due to alterations in both the guanine nucleotide-binding protein and the receptor.

Adenylyl Cyclases↗
PubMed1984

Heterogeneity of oxygen diffusion through hamster striated muscles.

We determined the O2 diffusion coefficients (DO2) and resting O2 consumptions for three hamster muscles with differing histochemical fiber type composition using a nonsteady-state technique. The muscles ranged from an oxidative muscle (soleus) to a glycolytic muscle (sartorius) with a third, the cheek pouch retractor, having mixed metabolic properties. We found that the DO2 of the soleus (corrected to 37 degrees C) was 2.59 +/- 0.33 X 10(-5) cm2/s, whereas the DO2 of the sartorius was 1.15 +/- 0.14 X 10(-5). The value for the retractor was between these two values (1.39 +/- 0.14 X 10(-5) cm2/s). In addition, we observed a linear correlation between DO2 and the percent of transverse cross-sectional area occupied by oxidative fibers, suggesting that the differences in DO2 can be accounted for by differences in their histochemical fiber type composition. In light of known differences in capillary density and maximal O2 demand, these data imply an interplay between capillarity and O2 diffusion rate resulting in an appropriate O2 delivery to meet each muscle's maximal O2 demand.

Animals↗
PubMed1984

In vitro O2 uptake and histochemical fiber type of resting hamster muscles.

In vitro oxygen consumption (VO2), histochemical fiber type, capillary arrangement, and muscle fiber geometry were measured in three hamster striated muscles. These muscles varied markedly in their histochemical fiber type composition (% by number): retractor (70% FG, fast-twitch, glycolytic; 16% FOG, fast-twitch, oxidative-glycolytic; 14% SO, slow-twitch, oxidative); soleus (57% FOG, 43% SO), and sartorius (98% FG, 2% FOG). Sartorius VO2 [0.80 +/- 0.034 (SE) ml O2 X min-1 X 100 g-1] was significantly different (P less than 0.01) from VO2 of retractor (0.89 +/- 0.038) and soleus (1.00 +/- 0.048). The number of capillaries around a fiber and the surface area/volume were greater for FOG and SO fibers than for FG fibers. Fibers of all types appeared to be roughly elliptical in shape. Capillaries were uniformly distributed around fibers in the soleus, but they were located more toward the ends of the major diameter in the retractor and sartorius. The results suggest a relationship among a fiber's oxidative capacity (based on its histochemical staining pattern), number of surrounding capillaries and surface area/volume. Furthermore, results suggest that VO2 and capillary spacing around a fiber may depend on fiber type.

Adenosine Triphosphatases↗
PubMed1984

Relationship between intrinsic activities of agonists in normal and desensitized tissue and agonist-induced loss of beta adrenergic receptors.

The intrinsic activities of 14 agonists at beta adrenergic receptors were determined in membranes prepared from control L6 muscle cells or from cells preincubated in the presence of isoproterenol for 20 min. Several drugs that were full agonists when studied with membranes from naive cells were partial agonists in membranes prepared from desensitized cells. Prolonged incubation of cells with agonists resulted in a 70 to 80% decrease in the density of beta adrenergic receptors. This effect was observed after incubation of cells with either full or partial agonists, suggesting that the extent of receptor loss is independent of the intrinsic activity of an agonist. The rate of receptor loss was related, however, to the intrinsic activity of an agonist. The rate of receptor loss correlated with the intrinsic activities of agonists in desensitized (r = 0.94) and control (r = 0.87) membranes.

Adenylyl Cyclases↗
PubMed1983

A computerized system for densitometric analysis of the microcirculation.

An analytical system for measuring size, motion, and light absorption of objects in the field of a microscope is described. The design criteria have been chosen to produce a system that permits acquisition of densitometric information at a number of points within the field and permits computation of important variables from the densitometric data. Relatively simple fiber-optics systems for sampling light intensity at selected locations in the microscope field are described. Computer programs are outlined that permit computation of microvessel diameter, red cell velocity, and hemoglobin oxygen saturation. The sampling systems and programs are quite general in nature and should be applicable to other types of related measurements and computing devices.

Capillaries↗
PubMed1983

Interactions of full and partial agonists with beta-adrenergic receptors on intact L6 muscle cells.

A nonfusing variant of L6 muscle cells was used to study the interactions of 16 agonists and 8 antagonists with beta-adrenergic receptors. Membranes prepared from L6 cells and intact cells in monolayer culture were used. Beta-adrenergic receptors on broken cells and on intact cells had the same affinities for all of the antagonists studied. Studies of the inhibition of the binding of [125I]iodohydroxybenzylpindolol by agonists indicated that two states of the receptor can exist on intact cells attached to the substratum. The form of the receptor normally present on intact cells appeared to have the same properties as receptors on membranes when assayed in the presence of GTP. Several full agonists converted this form of the receptor to a form which had a 40- to 50-fold lower affinity for agonists. This conversion appeared to occur during the first few minutes of exposure to an agonist. Four of the agonists tested did not convert any of the receptors on intact cells to a form with a low affinity for agonists. Included in this group of agents were two full agonists and two partial agonists. Therefore, interactions of these drugs with receptors on broken or intact cells were the same. Several other full and partial agonists converted some of the receptors on intact cells to a low-affinity form, and their interactions with receptors on intact cells were characterized by shallow inhibition curves. The conversion of beta-adrenergic receptors on intact cells to a low-affinity state did not appear to be a prerequisite for the decrease in the rate of agonist-stimulated cyclic AMP accumulation that occurs 1-2 min after exposure of L6 cells to agonists. Studies were also carried out on viable intact cells detached from plates following brief exposure to trypsin or EDTA. The properties of receptors on suspended cells were the same as those of receptors on broken cells when assayed in the presence of GTP, rather than being similar to the properties of receptors on attached cells. In summary, data are presented indicating that agonists with the same potency and intrinsic activity in membrane preparations (and intact cells in suspension) can interact very differently with beta-adrenergic receptors on intact cells attached to the substratum. Thus, certain agonists cause a rapid conversion of beta-adrenergic receptors to a form which has a low affinity for agonists. This effect is seen with some but not all agonists and is seen only in studies with attached cells.

Adrenergic beta-Agonists↗
PubMed1981

Selective survival of beta 1-adenergic receptors in rat cerebellum following neonatal x-irradiation.

Although beta 2-adrenergic receptors predominate in adult rat cerebellum, a small number of beta 1-receptors are also present. To investigate the cellular localization of beta 1- and beta 2-adrenergic receptors, the effects of intermittent neonatal X-irradiation focused on the cerebellum were determined on the densities of the two subtypes of beta-adrenergic receptor. This treatment destroys the late-maturing cerebellar interneurons including the granule, basket and stellate cells. A 60--70% loss of cerebellar mass was observed in 2-, 6- and 12-week-old animals. The large early-maturing Purkinje cells are resistant to the effects of X-irradiation. The total number of beta-adrenergic receptors per cerebellum, measured by Scatchard analysis of saturation isotherms of specific [125I]iodohydroxybenzylpindolol (IHYP) binding, was reduced by 70--80% in 2-, 6- and 12-week-old animals. The relative proportion of beta 1- and beta 2-receptors was determined by analyzing the inhibition of specific IHYP binding by the beta 1 selective antagonist practolol. The total number of beta 2-adrenergic receptors per cerebellum was reduced by 81--83% in 6- and 12-week-old X-irradiated rats. However, the number of beta 1-adrenergic receptors per cerebellum in 6- and 12-week-old X-irradiated rats was not significantly different from that in control animals. The results suggest that beta 2 receptors in the rat cerebellum are primarily associated with the small interneurons destroyed by neonatal X-irradiation. The beta 1 receptors may be located on a cell population which is unaffected by this treatment, possibly on cerebellar Purkinje cells.

Animals↗
PubMed1981

Interactions of agonists and antagonists with beta-adrenergic receptors.

The interactions of agonists and antagonists with beta-adrenergic receptors appear to be fundamentally different. Antagonists only occupy the receptor while agonists bind to the receptor and induce a specific conformational change. The excellent correlation between the efficacy of full or partial agonists and the magnitude of the changes in the thermodynamic parameters associated with the binding of these compounds suggests that this conformational change is related to the ability of various drugs to stimulate adenylate cyclase. In most instances it is difficult to distinguish an agonist from an antagonist using the in vitro binding of radiolabeled ligands. The thermodynamic analysis described here represents one example of a situation in which agonists and antagonists can be distinguished using in vitro binding techniques. The complexities of agonist interactions with beta-adrenergic receptors are also clearly seen in studies of binding to intact cells and in direct studies using radiolabeled agonists. In the former studies it appeared that there were marked changes in the properties of the receptor that occurred during the 60 min that are required for the binding of IHYP to beta-adrenergic receptors on L6 myoblasts to reach equilibrium. These changes make it difficult to analyze the affinity of the receptor for agonists using intact cells. Finally, the complexities of agonist interactions with the beta-adrenergic receptor are also seen in direct binding studies with radiolabeled agonists. The curvilinear Scatchard plots and the complicated dissociation kinetics attest to this complexity. The importance of the formation of a hypothetical ternary complex between hormone, receptor, and guanine nucleotide-binding regulatory protein is now becoming appreciated. The existence of other components of this system will remain an important subject for future investigation. In any case, it is clear that a full understanding of this system will require the use of not only radiolabeled agonists and antagonists but also of both broken and intact cells.

Adrenergic beta-Agonists↗
PubMed1980

Histamine-mediated delayed permeability response after scald burn inhibited by cimetidine or cold-water treatment.

Scald injury to one ear of the hairless mouse induced significant (P < .05) delayed edema formation in remote, uninjured skin. This remote edema formation was completely inhibited by immediate cold-water treatment of the scalded ear. Cold-water treatment significantly reduced histamine loss from the scalded ear, and the edema-inhibiting effect of the treatment could be mimicked by treating the animal prior to injury with the H2-histamine receptor antagonist cimetidine or a drug that causes histamine depletion. These observations suggest (i) that a histamine-mediated, delayed permeability response occurs after thermal injury that causes remote edema formation and (ii) that one mechanism of remote edema inhibition by cold-water treatment is the prevention of histamine release from thermally injured tissues.

Animals↗
PubMed1980

Ontogeny of beta 1- and beta 2-adrenergic receptors in rat cerebellum and cerebral cortex.

The development of beta 1- and beta 2-adrenergic receptors was studied in rat cerebral cortex and cerebellum. In the cerebral cortex, which contains mostly beta 1-adrenergic receptors, total beta-adrenergic receptor density increased sharply between postnatal days 10 and 21. The density of receptors remained fairly constant through 6 weeks of age and then subsequently declined. The proportion of beta 1 and beta 2 receptors was relatively constant throughout the development of the cerebral cortex. The development of the two receptor subtypes thus paralleled the development of total beta-adrenergic receptors in the cerebral cortex. The ontogeny of beta-adrenergic receptors in the cerebellum, which contains mainly beta 2 receptors, was strikingly different from that observed in the cortex. Total cerebellar beta receptor density exhibited a slow but steady increase from postnatal day 5 through day 42. The density of receptors then plateaued and remained constant until the animals were approximately 6 months of age. Unlike the results obtained in the cortex, the relative proportions of beta 1 and beta 2 receptors in the cerebellum changed markedly during development. Between postnatal days 8 and 13 approximately 18% of the receptors were of the beta 1 subtype. This proportion steadily decreased with age, and in 3- and 6-month-old animals only approximately 2% of the receptors were of the beta 1 subtype. The results demonstrate that the two subtypes of beta-adrenergic receptors can have different developmental patterns in the same brain area, and that a single receptor subtype can follow different developmental patterns in different brain regions. Possible correlations between the ontogeny of beta 1 and beta 2 receptors and various developmental events are discussed.

Aging↗