Biomedical subjects

G J Christ

Publications and source records attributed to G J Christ.

80 records · Page 5Linked to original sources

PubMed1990

Pharmacological studies of human erectile tissue: characteristics of spontaneous contractions and alterations in alpha-adrenoceptor responsiveness with age and disease in isolated tissues.

1. The pathophysiology of impotence related to vascular smooth muscle dysfunction in the male corpus cavernosum was studied on human isolated erectile tissue (HET). Studies were conducted on 140 sections of HET obtained from 38 male patients undergoing surgery for implantation of penile prostheses to correct underlying erectile dysfunction. 2. Spontaneous myotonic oscillations were characteristic of greater than 90% of all HET preparations at 37 degrees C. These spontaneous oscillations were markedly attenuated by indomethacin, BW755C, nifedipine, removal of extracellular Ca2+, or lower temperatures (less than or equal to 32 degrees C), but were not sensitive to inhibition by atropine, phentolamine or tetrodotoxin. Our data suggest that the oscillations may, at least in part, result from the generation and/or release of a stable cyclo-oxygenase product and a consequent increase in transmembrane Ca2+ influx. 3. The phenylephrine-induced contractions in HET may be reliably assayed up to 24 h after surgical removal, without significant alterations in the EC50, maximum response (Emax) or slope index of the steady-state concentration-response curve to phenylephrine. 4. The competitive and surmountable nature of the antagonism of phenylephrine-induced contractions by prazosin and yohimbine allowed calculation of antagonist dissociation constants. The calculated pKb values for prazosin and yohimbine, respectively, were 9.47 +/- 0.49 and 5.54 +/- 0.22. The rank order of agonist potency in HET was: noradrenaline = phenylephrine much greater than clonidine. These data indicate the presence of a population of membrane receptors that are predominantly of the alpha 1-adrenoceptor subtype. 5. The entire patient population was stratified on a decennial basis into five age groups, and each age group was subsequently subdivided into diabetic and nondiabetic diagnostic categories. With respect to the steady-state phenylephrine concentration-response curves, a Winer two-factor analysis of variance revealed a significant effect of age on the calculated pEC50 value, as well as a significant age-diagnosis interaction. A post hoc statistical analysis for unpaired samples yielded significant differences between pEC50 values for diabetic and nondiabetic patients in age groups 41-50 and 61-70 years. In addition, a Winer two-factor analysis of variance also detected a significant effect of age on the calculated E.., value. 6. In conclusion, our studies demonstrate that spontaneous contractions in HET are likely to be mediated by the generation and release of a stable cyclo-oxygenase product. Furthermore, the results of both agonist and antagonist studies are consistent with the presence of a homogeneous alpha x-adrenoceptor population. Lastly, the responsiveness of isolated HET to phenylephrine was shown to be altered by both age and disease.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1990

Receptor-mediated mutual-effect amplification elicited by phenylephrine and serotonin in isolated rabbit aorta.

Phenylephrine (PE) and 5-hydroxytryptamine (5-HT) were utilized to study the effects of simultaneous coactivation of the alpha-1 and 5-HT2 receptors, respectively, on the contractile response of isolated rabbit aortic rings. A mutual-effect amplification of the PE-induced contractile response was observed with concentration-response curves (CRC) elicited by mixtures of PE and 5-HT, using a novel drug concentration paradigm. The theoretical CRC constructed using the Poch and Holzman method of equiactive agonist substitution demonstrated that the observed mutual-effect amplification was more than the result of simple additivity. Thus, the Leff model of mutual-effect amplification was utilized to predict the location of observed CRCs to mixtures of PE and 5-HT. Efficacy (tau) and slope factor estimates were determined using the Black and Leff operational model of pharmacological agonism and these values were used to predict the location of CRCs elicited by mixtures of PE and 5-HT. We demonstrated that the Leff model was insufficient to explain the observed degree of mutual-effect amplification.

Animals↗

PubMed1988

Genetic influences on agonist binding to cardiac beta-receptors.

Regulation of beta-adrenoceptor-agonist function in the Maudsley Reactive (MR/Har) and the Maudsley Non-Reactive (MNRA/Har) rat strains was assessed by comparison of isoproterenol competition for [125I]iodocyanopindolol (ICYP) binding sites in crude left ventricular homogenate preparations. Non-linear, least-squares analysis of isoproterenol competition for ICYP binding in the absence of guanine nucleotide revealed different proportions of high- and low-affinity receptors in the two strains; MR/Har rats (59 +/- 3.3%) had a significantly greater proportion of receptors in the high-affinity state than the MNRA/Har rats (41 +/- 4.5%). Addition of the non-hydrolyzable guanine nucleotide analog guanylylimidodiphosphate (Gpp(NH)p) converted receptors to the low-affinity state. Analysis of Gpp(NH)p concentration-response curves in left ventricular homogenates of the two strains revealed that the MR/Har strain had a significantly (P less than 0.02) lower EC50 for guanyl nucleotide inhibition of isoproterenol competition for ICYP binding than the MNRA/Har. Confirming previous experimental results, a significantly (P less than 0.04) greater density of ventricular beta-receptors was found in MR/Har rats (13.16 +/- 0.92 fmol/mg protein) than in MNRA/Har rats (10.81 +/- 0.63 fmol/mg protein). Left ventricular catecholamine levels were found to be correlated inversely with beta-adrenoceptor density in the two strains; norepinephrine (NE) and epinephrine (EPI) concentrations (ng/mg protein) in left ventricle were 12.19 +/- 0.94 for NE and 0.165 +/- 0.038 for EPI in MNRA/Har, and 8.73 +/- 0.95 and 0.018 +/- 0.018, respectively, in MR/Har. All other parameters of agonist interactions with the cardiac beta-adrenoceptor for the MR/Har and MNRA/Har rat strains were similar [the IC50 for displacement of ICYP binding by isoproterenol, the accompanying Hill coefficients in the Gpp(NH)p present and absent condition, the Kd of the high- and low-affinity states in the absence of Gpp(NH)p, and the Kd of the uniform low-affinity state in the presence of Gpp(NH)p]. We hypothesize that the strain-dependent differences in high-affinity state formation reported here may account for some of the in vivo differences in cardiovascular function previously demonstrated in the Maudsley rats.

Adrenergic beta-Agonists↗

PubMed1988

Effects of stress and chronic propranolol infusion on cardiac beta-receptor function in the Maudsley Reactive and Non-Reactive rat strains.

The effects of beta-adrenoceptor blockade on left ventricular beta-receptor characteristics were evaluated in the Maudsley Reactive (MR/Har) and Non-Reactive (MNRA/Har) rat strains. After propranolol infusion for one week administered by subcutaneously implanted osmotic minipumps, differences in beta-adrenoceptor-agonist interactions between strains were assessed by comparison of isoproterenol competition for [125I]iodocyanopindolol (ICYP) binding sites in crude left ventricular homogenate preparations from both strains. Propranolol exposure had no significant effect on the binding parameters investigated (Bmax, Kd, % receptors in high affinity state, IC50). In contrast to previous observations in naive animals, these experiments revealed no strain differences in the sham-implanted Maudsleys in any of the left ventricular beta-adrenoceptor parameters investigated. We hypothesize that the surgical procedures and/or presence of the plastic inserts acted as stressors in the Maudsley strains and thus altered beta-adrenoceptor function. This hypothesis is supported by the observation that exposure to another stress (footshock) also eliminated strain differences in ventricular beta-receptor binding variables.

Animals↗

PubMed1986

Characterization of opioid receptor binding in adult and fetal sheep brain regions.

Opioid receptor binding was studied in 3 brain regions from maternal and fetal sheep at various gestational ages. [3H]dihydromorphine [( 3H]DHM) and [3H]D-Ala2,D-Leu5-enkephalin ([3H]DADLE) were employed as radioligands to characterize mu- and delta-opioid receptor binding sites, respectively. [3H]DHM binding was found to be highest in maternal cerebellum, intermediate in frontal cortex, and lowest in hippocampus. [3H]DADLE binding was highest in frontal cortex, intermediate in hippocampus and lowest in cerebellum. Cerebellum was the only tissue studied which contained more [3H]DHM than [3H]DADLE binding sites. Dissociation constants for [3H]DHM binding were similar in all 3 brain regions from both maternal and fetal sheep, while the dissociation constant for [3H]DADLE binding was significantly higher in cerebellum than in frontal cortex or hippocampus. Binding of both mu- and delta-receptor-selective ligands was 70% of maternal values in fetal cerebellum at 97-101 days of gestation and gradually increased over the remainder of the gestational period studied. Levels of [3H]DHM binding in frontal cortex and hippocampus were also similar to maternal levels at all timepoints studied. In contrast, [3H]DADLE binding was only 40-45% of maternal levels in fetal frontal cortex and hippocampus prior to 110 days of gestation, followed by a rapid increase in binding in both brain regions.

Aging↗

PubMedDate not supplied

Myocardial expression of endothelin-1 in murine Trypanosoma cruzi infection.

Chagas' disease, caused by Trypanosoma cruzi, is an important cause of myocarditis and chronic cardiomyopathy and is accompanied by microvascular spasm and myocardial ischemia. We reported previously that infection of cultured endothelial cells with T. cruzi increased the synthesis of biologically active endothlein-1 (ET-1). In the present study, we examined the role of ET-1 in the cardiovascular system of CD1 mice infected with the Brazil strain of T. cruzi and C57BL/6 mice infected with the Tulahuen strain during acute infection. In the myocardium of infected mice myonecrosis and multiple pseudocysts were observed. There was also an intense vasculitis of the aorta, coronary artery, smaller myocardial vessels and the endocardial endothelium. Immunohistochemistry studies employing anti-ET-1 antibody revealed increased expression of ET-1 that was most intense in the endocardial and vascular endothelium. Elevated levels of mRNA for preproET-1, endothelin converting enzyme and ET-1 were observed in the same myocardial samples. Plasma ET-1 levels were significantly elevated in infected CD1 mice 10-15 days post infection. These observations suggest that increased levels of ET-1 are a consequence of the initial invasion of the cardiovascular system and provide a mechanism for infection-associated myocardial dysfunction.

Animals↗

PubMedDate not supplied

Gene therapy: future strategies and therapies.

Significant advances have been made in the past decade concerning the mechanistic basis for the control of penile erection and the etiology of erectile failure. The combined efforts and accumulated wisdom of urologic scientists and clinicians around the world have ensured that these basic advances have translated into the remarkable success recently observed in the treatment of erectile dysfunction. In fact, erectile function can now be effectively restored in every man with the requisite level of desire and motivation. Nonetheless, all of the currently available treatment options have either limited efficacy, significant and untoward side effects, or both. There is clearly room for improvement. However, improved therapy of erectile dysfunction is dependent on garnering even more precise details concerning the regulation of human corporal smooth muscle tone, and furthermore, on the identification of relevant molecular targets. The next generation of erectile dysfunction therapies, therefore, will necessarily require the application of molecular technologies to the study of erectile physiology/dysfunction. One such application is the utilization of gene therapy approaches. This report outlines the overall goals and promise of gene therapy for the treatment of human erectile dysfunction and briefly reviews a few initial strategies to that end.

Journal Article↗

PubMedDate not supplied

Characterization of K currents in cultured human corporal smooth muscle cells.

In order to gain more mechanistic insight into the regulation of corporal smooth muscle tone, we conducted electrophysiological studies on homogeneous explant cell cultures of human corpus cavernosum smooth muscle. Patch clamp analyses in the whole cell mode revealed a mean resting potential of -43 +/- 4.9 m V (n = 12 cells). Large whole cell outward K currents were very prominent in these cells, and ranged from 0.5 to 1.5 nA. In some cells, a transient, voltage-dependent A current accounted for a significant portion of the observed whole cell currents. Furthermore, stimulation with the calcium channel agonist BAY K 8644 or the K channel agonist pinacidil doubled the magnitude of the whole cell K current, as would be expected for maxi-K (KCa) and metabolically gated K channels (KATP), respectively. Single channel recordings in the detached patch mode consistently revealed the presence of at least two K channels: 1) a KCa channel, with a conductance of approximately 190 pS; and 2) a putative delayed rectifier channel with a conductance of approximately 50 pS. Furthermore, all channel types showed some degree of voltage and/or calcium sensitivity. In conclusion, the large magnitude of the whole cell K currents and the observed K channel heterogeneity indicate a potentially important role for these channels in modulating corporal smooth muscle tone.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗