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C C Loullis

Publications and source records attributed to C C Loullis.

14 recordsLinked to original sources
PubMed1992

A proposed mechanism of action of a growth hormone-specific monoclonal antibody in the enhancement of hormonal activity.

The potentiation of the biological activity of recombinant porcine growth hormone (pGH) by immunologic manipulation was investigated. An anti-pGH monoclonal antibody, designated PS-7.6, was generated and its effect on pGH was evaluated in hypophysectomized (hypox) rats. As expected, administration with pGH for 5 consecutive days promoted these animals to grow. The effect was further augmented when pGH was given together with PS-7.6 antibody and the enhancing ability of the antibody lasted beyond the treatment period. The growth profile of rats receiving antibody alone did not differ from that of untreated controls, indicating that PS-7.6 antibody by itself was not a growth stimulant. The possible mechanism of action of the antibody was investigated by analyzing blood and tissue samples of animals following injection with 125I-labeled pGH either in its free form or complexed with PS-7.6 antibody. As compared to the pGH levels in animals receiving free pGH, approximately a half pGH was released into circulation from the injection sites when it was given in a complex form. Furthermore, 2-4-fold increases in pGH deposition were also found in various tissues of animals treated with pGH-antibody complexes over that of respective tissues of animals receiving free pGH. Therefore, the present findings suggest that PS-7.6 antibody is capable of augmenting the somatogenesis of pGH and the effect is, at least in part, explainable by its ability in altering the pharmacokinetics and biodistribution of pGH in animals.

Animals↗
PubMed1989

Characterization of ligand binding to mitochondrial benzodiazepine receptors.

We have evaluated the affinity and density of binding sites for [3H]Ro5-4864 and [3H]PK11195 in intact and fragmented rat kidney mitochondria. These sites are known as peripheral-type or mitochondrial benzodiazepine receptors (MBR) and the preceding paper provided evidence that they function in vitro as modulators of mitochondrial respiratory control (1). In this report, MBR density, localization, and ligand specificity were investigated. In intact mitochondria, there were approximately the same number of binding sites for [3H]PK11195 as for [3H]Ro5-4864, and their apparent Kd values were identical. However, in mitochondrial fragments, there were 80% more binding sites for [3H]Ro5-4864 than for [3H]PK01195. Rat kidney mitochondria were fractionated by decompression and digitonin-based methods into outer and inner membrane-containing fractions before and after incorporation of the MBR-specific photoaffinity ligand [3H]PK14105. Assays of selective mitochondrial membrane markers and [3H]Ro5-4864 binding or specifically bound [3H]PK14105 revealed that the receptors were found in the mitochondrial outer membrane. We also evaluated the binding of a large number of structurally and pharmacologically diverse compounds to MBR by studying their ability to inhibit the binding of both 3H-ligands. These compounds had affinities ranging from 0.015 to 100 microM and, with a few exceptions, were similar in their abilities to bind to MBR in intact and fragmented mitochondria. However, there was considerable variation in the ratios between drug potencies at displacing [3H]Ro5-4864 and [3H]PK11195. This represents a new form of evidence that these two radioligands do not label identical sites on the receptor. Thirteen of the drugs, including [3H]Ro5-4864 and [3H]PK11195, were analyzed as to the nature of the inhibition and, with only two exceptions, were competitive inhibitors. One drug, Konig's polyanion, was uncompetitive whereas the other, cyclosporin A, was a noncompetitive inhibitor. These studies revealed several new classes of MBR ligands and suggest that the relationship between ligand structure and binding affinity is highly complex.

Animals↗
PubMed1985

Hippocampal muscarinic receptor loss following trimethyl tin administration.

The effects of trimethyl tin on passive and active avoidance behavior, hippocampal muscarinic receptors and hippocampal cell destruction were examined in male rats. The animals were intubated with 18 mumoles/kg (3.5 mg/kg) of TMT hydrochloride or vehicle. When tested two weeks later treated animals exhibited marked deficits in retention of passive avoidance and extinction of active avoidance tasks. Receptor binding analysis, using 3H-QNB, revealed a significant decrease (21%) in muscarinic receptor density in the hippocampus. Histological examination of the hippocampus revealed a concomitant loss in pyramidal cells in these animals. These results suggest that muscarinic receptors reside on the hippocampal pyramidal cells and that these cells and receptors may be involved in retention of passive avoidance behavior.

Animals↗
PubMed1985

Conformational changes in muscarinic receptors may produce diminished cholinergic neurotransmission and memory deficits in aged rats.

Both clinical and laboratory studies suggest that age-related memory deficits may be due, at least in part, to disturbances in muscarinic acetylcholine (mAChR) receptors. In order to further evaluate this premise, the present studies examined the electrophysiological responses rates of hippocampal pyramidal cells to iontophoretically applied ACh in young, middle-age and aged animals. The relationship between age and muscarinic agonist and antagonist binding in the hippocampus was also examined. In addition, possible age-related changes in receptor-effector coupling were assessed by determining calmodulin levels and the activities of phospholipid methyl-transferase I and II. Analysis of electrophysiological data showed selective age-related decrements in the ability of ACh to alter burst rate but not simple spike rate. These age-related decreases in the efficacy of ACh to increase burst rate were not paralleled by decreases in mAChR density as assessed by 3H-QNB binding, but they were temporally paralleled by age-related changes in the ability of oxotremorine to inhibit 3H-QNB binding. In the young animals, the resultant Hill coefficients derived from these analyses approached 1, while in the middle and old aged animals, the Hill coefficients deviated significantly from 1, indicating the possible existence of 2 or more receptor states with differential affinity for oxotremorine in the 2 older age groups. When carbamylcholine was used to inhibit 3H-QNB, these complex binding patterns were seen even in the young, since carbamylcholine induces conformational/orientational changes in the mAChR while oxotremorine does not.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1985

Assay of brain calmodulin levels using high-performance liquid chromatography.

A simple, sensitive, and efficient HPLC method for the determination of calmodulin levels in brain tissue extracts is described. The assay is linear with respect to both calmodulin and protein concentrations. The specificity and validity of this assay for calmodulin is demonstrated by parallel radioimmunoassay determinations which give equivalent results. Determination of calmodulin levels in various brain regions revealed a high concentration of this protein in the hypothalamus, by comparison to other areas examined.

Animals↗
PubMed1983

Chronic administration of cholinergic agents: effects on behavior and calmodulin.

Rats were implanted subcutaneously with Alza pumps and 0.9% saline, physostigmine, or scopolamine were continuously infused for 15 days. Twenty-four hours after removal of the pumps all animals were trained on a single trail passive avoidance task. Twenty-four hours after training they were tested for retention. Following behavioral testing, animals were sacrificed, brain regions dissected, frozen and stored (-20 degrees C) for calmodulin determinations. Animals which had previously received chronic infusions of scopolamine performed significantly better than controls, while those which previously received chronic infusions of physostigmine performed significantly worse during the retention test. No significant differences in calmodulin levels (soluble or particulate) were detected across brain regions or drug groups. These results indicate that continuous chronic infusion of drugs which can facilitate or inhibit CNS cholinergic activity can induce performance changes on a learning task opposite to those resulting following the acute administration of these same drugs.

Animals↗
PubMed1979

HPLC determination of biogenic amines in discrete brain areas in food deprived rats.

Norepinephrine (NE), dopamine (DA), 5-hydroxytryptophan (5-HTP), 5-hydroxytryptamine (5-HT), and 5-hydroxyindole acetic acid (5-HIAA) levels in the lateral hypothalamus (LH), ventromedial hypothalamus (VMH), median raphe (MR) and dorsal raphe (DR) were determined in nondeprived and 48 hr food deprived rats. Simultaneous determination of these compounds was accomplished by means of high performance liquid chromatography (HPLC) with electrochemical detection. When compared with controls, food deprived animals showed significant increases in 5-HT and 5-HIAA levels in the raphe nuclei, significant increases in 5-HIAA in the LH, but no changes in either 5-HT or 5-HIAA levels in the VMH. No changes in catecholamine levels were found in any of the brain areas studied. These results show that indoles in the raphe nuclei, as well as in the LH, are affected by food deprivation. The lack of change in indole levels in the VMH indicates that specific nuclei within the hypothalamus are differentially affected by food deprivation.

Animals↗