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R L Meyer

Publications and source records attributed to R L Meyer.

89 records · Page 5Linked to original sources
PubMed1982

Vasodilator actions of several N-nitroso compounds.

Recent studies have shown that N-nitroso compounds can activate arterial guanylate cyclase and relax isolated arterial smooth muscle; however, the effects of these substances on the cardiovascular system in the anesthetized cat are unknown. The present study was undertaken to compare the effects of several nitrosoguanidines and a nitrosamine, N-nitrosodimethylamine, on arterial guanylate cyclase activity, isolated arterial smooth muscle tone, and systemic vascular resistance in the anesthetized cat. Intravenous injections and infusions of the nitrosoguanidines glyceryl trinitrate (GTN) and sodium nitroprusside (SNP) decreased systemic arterial pressure. During intravenous infusion of the nitrosoguanidines GTN and SNP, cardiac output was unchanged at the peak of the decrease in aortic pressure, indicating that the nitrosoguanidines GTN and SNP both reduced systemic vascular resistance. In addition, intraarterial injections of the nitrosoguanidines produced dose-dependent decreases in perfusion pressure in the feline mesenteric vascular bed perfused at constant flow. These substances were potent relaxants of isolated arterial smooth muscle and markedly activated arterial guanylate cyclase. In contrast, N-nitrosodimethylamine was devoid of vasodilator activity in vivo and exerted only minimal effects on isolated arterial smooth muscle tone or on arterial guanylate cyclase activity. The present data demonstrate a relationship between guanylate cyclase activation and arterial smooth muscle relaxation and suggest that the vasodilator effects on resistance vessels in vivo in response to selected N-nitroso compounds may involve such a mechanism. Although the significance of the presently reported cardiovascular responses to N-nitroso compounds is uncertain, N-nitroso compounds may represent a previously unrecognized class of substances which can be formed in the body and which possess marked vasodilator activity. It is possible that this vasodilator activity may involve the relaxation of vascular smooth muscle through activation of guanylate cyclase.

Animals↗
PubMed1981

Analysis of responses to dopamine in the mesenteric vascular bed of the cat.

Responses to dopamine were investigated in the feline mesenteric vascular bed under conditions of controlled blood flow. Intra-arterial injections of dopamine in doses of 3, 10 and 30 microgram caused biphasic changes in mesenteric arterial perfusion pressure. The pressor component of the biphasic response was blocked whereas the depressor component was enhanced after administration of phenoxybenzamine in a dose that reversed vasoconstrictor responses to norepinephrine. Depressor responses to dopamine in phenoxybenzamine treated animals were not blocked by propranolol or atropine in doses that inhibited responses to isoproterenol or acetylcholine or by indomethacin in a dose that inhibited responses to the prostaglandin precursor arachidonic acid. Depressor responses to dopamine were inhibited by bulbocapnine in a dose that was without significant effect on depressor responses to isoproterenol or nitroglycerin. The inhibitory effects of bulbocapnine were reversible and vasodepressor response to dopamine returned to control levels 15-30 min after the bulbocapnine infusion was discontinued. These data suggest that the pressor effects of dopamine in the feline mesenteric vascular bed are due to activation of alpha adrenergic receptors whereas the vasodilator activity results from activation of vascular dopamine receptors that are distinct from beta adrenergic or cholinergic receptors and does not involve the release of dilator prostaglandin.

Animals↗
PubMed1981

[Geriatric care in a rural practice].

Geriatric care in a rural practice. General practitioners/family physicians are responsible for the continuing care in case of illness and infirmity of about 95% of the population over 65 years old. In the examined practice area the percentage of the population over 65 years old is 11.29, but among the patients of the practice 18.5% are over 65 years old and the consultations come up to a percentage of 21.6. A random test by 100 patients over 65 years old during half a year has given the following facts: There have been 946 consultations, 299 of them as home visits. 18 patients needed 28 hospitalisations with a total of 481 days as in-patients. 6 patients died during the test period. On an average 4.44 diagnoses were needed and 7.63 medicaments prescribed. By 67 patients 85 heavy, acute troubles occurred. These facts show the importance of the geriatric aspects in the primary care. Since the percentage of the older patients is growing also with the growing age of the doctor, it is necessary that more attention must be given in the continuing education to the problems of geriatric care, of multimorbidity, of multimedication and of alternatives to medical therapy.

Adolescent↗
PubMed1980

The enhancement effect of irradiation by methotrexate. Report of three complications.

Three cases are described in which complications developed which were believed to be due to the enhancement effect of irradiation by methotrexate during the course of therapy for lung, kidney, and bladder cancer. These included esophageal and large bowel complications. In two of these cases, the patients improved with conservative therapy.

Aged↗
PubMed1980

Mapping the normal and regenerating retinotectal projection of goldfish with autoradiographic methods.

In normal goldfish, lesions of various size were made in nasal or temporal retina immediately prior to retinal labeling with tritiated proline. The resulting gaps in retinal innervation of tectum indicated that the projection is retinotopographically ordered to a precision of about 50 micrometer. Similarly, acute tectal incisions transecting the optic pathways were combined with immediate retinal labeling. The resulting tectal denervation confirmed that most fibers follow highly ordered paths through the stratum opticum of tectum; but a few fibers were found to follow unusual paths to their appropriate tectal positions. In other fish, the optic nerve was crushed. At various times afterwards, retinotopography and pathway order were similarly analyzed by making retinal lesions or tectal incisions just prior to labeling. For up to 40 days after crush, the projection lacked any refined retinotopic order. Only a gross topography could be demonstrated. Over several months, retinotopography gradually improved eventually approaching that of normals. Correlated with this was an initial stereotypic growth through the pathways of the stratum opticum followed by a long period of highly anomalous growth through the innervation layer. Evidently, many regenerated fibers grew in through inappropriate routes to the wrong region of tectum but subsequently arrived at their appropriate locus by circuitous routes within the innervation layer.

Animals↗
PubMed1979

Retinotectal projection in goldfish to an inappropriate region with a reversal in polarity.

An abnormal, ipsilateral projection was formed by deflecting optic fibers that normally innervate the posterior part of one tectum into the anterior end of the opposite tectum. When anterior recipient tectum was simultaneously denervate, the deflected fibers formed a retinotopic map in this region that was reversed with respect to the anterior-posterior tectal axis.

Animals↗
PubMed1979

"Extra" optic fibers exclude normal fibers from tectal regions in goldfish.

A small group of selected optic fibers were surgically deflected from one tectum into the other, thus creating a novel additional projection originating from a small area of ipsilateral retina. The normal fibers to this "recipient" tectum were also severed so that both the deflected and the normal fibers regrew into this tectum at about the same time. The reinnervation pattern was analyzed by autoradiography and electrophysiologic mapping. Both techniques showed that the deflected fibers and the "normal" fibers failed to intermix. The deflected fibers typically formed several well-defined patches of innervation in roughly the appropriate region of denervated recipient tectum. The normal fibers filled in the remaining uninnervated tectal areas and were completely or nearly completely exculded from the patches occupied by the deflected fibers. This segregation was often quite sharp having an apparent average overlap less than 25-50 micron. The electrophysiology indicated that the projections of both deflected and normal fibers were retinotopically organized but that the mapping by the normal fibers was compressed. This compression, an apparent consequence of being squeezed onto a smaller than normal region of tectum, was similar to that previously observed following ablations of part of the tectum. The negligible surgical damage in the present experiment, however, excludes the kind of cytochemical reorganization previously suggested to produce compression. The findings also provide evidence for a competitive type of interaction between optic fibers.

Animals↗
PubMed1978

Deflection of selected optic fibers into a denervated tectum in goldfish.

In goldfish, one eye was enucleated, and after two or more weeks a select fraction of optic fibers from the remaining eye was deflected into the ipsilateral optic tectum. At varying intervals, the optic reinnervation of the ipsilateral tectum was measured by autoradiography and electrophysiologic mapping. Both methods indicated the deflected optic fibers not only innervated the appropriate region of tectum but also spread beyond this, occupying a total area that was several times greater than normal. Correlated with this spreading were low grain density in the autoradiograms and reduction in the number of amplitudes of units recorded electrophysiologically. The electrophysiology also revealed this projection to be almost devoid of topographic organization, showing only a crude but appropriate polarity.

Animals↗
PubMedDate not supplied

Fine retinotopic organization of optic terminal arbors in the tectum of normal goldfish.

Although the retinotectal projection of goldfish has long been known to have a high degree of retinotopic order, the structural basis for this in terms of the precise positioning of axonal arbors from neighboring retinal ganglion cells has not been determined. In studying this, a small number of neighboring retinal ganglion cells was selectively labeled by a microinjection of DiI into the retina. Following axoplasmic transport for several days, the tectum was removed and flat-mounted for fluorescence microscopy. The injection labeled a small number of axons and their terminal arbors which ranged in size from 108 x 134 microm to 394 x 331 microm with a mean of 233 x 219 microm. This mean size corresponds to about 1/15 of the length of one tectal axis. Although individual arbors labeled from one small retinal injection were always observed near the same retinotopic position, they were almost never coextensive. Overlap between pairs of arbors along the lines of projection perpendicular to the tectal surface averaged 57% of the area of a single arbor. These results indicate that neighboring retinal ganglion cells do not converge onto the same locus but instead project as a continuous retinotopic array of partially overlapping terminal fields.

Animals↗