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Biomedical subjects

C Hammer

Publications and source records attributed to C Hammer.

At least 289 records · Page 16Linked to original sources
PubMed1968

An experimental space combining individual and social performances.

This report describes several primate environments in which two or more animals shared a common social area. Automatic programming was used to permit concurrent individual sessions. Some of the behavioral phenomena observed in these environments, including reinforcing properties of social interactions, are discussed.

Aggression↗
PubMedDate not supplied

Ethinylestradiol stimulates a biliary cholesterol-phospholipid cosecretion mechanism in the hamster.

The mechanism of ethinylestradiol-induced biliary secretion of excess cholesterol, a potential causative factor of cholesterol gallstones, is not yet known. It might be related to altered bile acid metabolism, since the rate of cholesterol and phospholipid secreted into bile is thought to be influenced by the hydrophobicity of the bile acid species secreted. We therefore studied the effect of ethinylestradiol on bile acid metabolism and on secretory relationships between taurocholate and cholesterol/phospholipids in bile. Litter-matched Syrian female hamsters (80 to 100 gm body weight) were injected subcutaneously with either 0.2 ml per day corn oil (controls) or a pharmacologic dose of 5 mg per kg per day ethinylestradiol in corn oil (EE-hamsters; n = 6) for 5 days. On Day 6, bile was collected for 60 min (basal secretory rate) via a bile duct fistula after exclusion of the gallbladder. Then, a graded infusion of taurocholate was given for 110 to 130 min. Secretory rates (nmoles.min-1.-1 liver) for bile acids, cholesterol and phospholipids were determined and their mutual "linkage coefficients" (nmoles of secretory increment per 1 nmole of bile acid secreted) calculated by linear regression analysis. EE-hamsters had higher (p less than 0.02) basal secretory rates of cholesterol (0.71 +/- 0.21 vs. 0.45 +/- 0.10) and phospholipids (5.74 +/- 1.04 vs. 4.21 +/- 0.73) than controls at comparable bile flow and bile salt secretion rates. Cholic acid pool size and the fractional composition of bile acid species in bile were similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Xenoreactive natural antibodies and induced antibodies--their effects of beating cardiomyocytes as a model of a xenograft.

Xenotransplantation has been complicated by hyperacute rejection reactions, which are supposedly triggered by preformed natural antibodies (PNAb) of the recipient organism, whereas the role of antibodies specifically induced by previous antigen contact (IAb) is less clear. Primary cultures of spontaneously beating neonatal rat cardiomyocytes were used as a model of the heart to elaborate the effects of both PNAb and IAb from xenogeneic species and to investigate into their mechanisms of action. An experimental setup allowing for rapid medium exchange under continuous observation was employed. Sera containing PNAb reproducibly bring about a stereotype pattern of altered contractility including an initial increase in beating frequency followed by a temporary cessation of beating within the first minutes after administration. After recovery of spontaneous contractions, the cells within the monolayer exhibited a dissociation of the synchronicity of the beating persisting for several hours. The temporary pause in beating was prevented by a very high extracellular calcium concentration, but not by extracellular electrical stimulation sufficient to trigger contractions in control cells. Electrophysiological measurements carried out in adult ventricular guinea pig heart muscle cells under the same experimental conditions revealed an increase of the excitation threshold of the cells after application of sera containing PNAb due to an enhanced input resistance. These results indicate that the effect of PNAb is the consequence rather of a generally reduced excitability of the cell than of the inhibition of a singular ionic conductance. After specific absorption of PNAb directed against rat antigens beating of neonatal rate cardiomyocytes ensued without interruption. Sera specimens devoid of complement produced similar effects on contractility, although the duration of the standstill period was significantly shorter. The increase in input resistance visualized in guinea pig myocytes was absent after removing PNAb against guinea pig antigens but not after absorbing PNAb directed against rat epitopes. Signs of a permanent cytotoxicity after the administration of PNAb were lacking in all experiments. IAb against rat heart tissue raised in rabbits stopped the contractions of neonatal rat cardiomyocytes within 30 min after administration irreversibly and lead concentration-dependently to a destruction of the cells.

Animals↗