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Biomedical subjects

J Hahn

Publications and source records attributed to J Hahn.

At least 163 records · Page 9Linked to original sources
PubMed1980

Posttranscriptional regulation of an erythromycin resistance protein specified by plasmic pE194.

Induction of the synthesis of a plasmid-encoded polypeptide (E3) by erythromycin is known to be required for the inducible expression of resistance to the macrolide-lincosamide-streptogramin B group of antibiotics in Bacillus subtilis strains carrying the plasmid pE194. This resistance is mediated by a specific N6-dimethylation of adenine in the 23S rRNA of the large ribosomal subunit. We show in this report that E3 induction is regulated posttranscriptionally in the sense that it can occur when RNA synthesis is blocked and that induction is accompanied by an increase in the functional half-life of E3 mRNA but not of the mRNA species that code for the remaining four known pE194 polypeptides. The induction of E3 is subject to feedback regulation and involves the ribosome. Modification of the erythromycin binding site on the ribosome by methylation or by mutation interferes with induction.

Bacillus subtilis↗
PubMed1980

Brain stem auditory evoked potentials in determining site of lesion of brain stem gliomas in children.

Brain stem auditory evoked potential (BAEP) test results are reported on seven children (2 1/2-13 years) with brain stem neoplasms. In each case, the BAEP test results clearly indicated the site of lesion as determined by computerized tomography and observation during surgery. Seven criteria for the assessment of BAEP test results are also presented: 1. Peak latency, 2. Intra-peak latency, 3. Inter-peak latency, 4. Response stability, 5. Amplitude, 6. Waveshape, and 7. Peak presence. Six children had positive indications on at least four of the seven criteria described, while one child had two positive indications. However, dramatic abnormality on any single criterion warrants serious investigation.

Adolescent↗
PubMed1978

Adaptation to extrauterine existence: cardiac and respiratory rates during the first 72 hours.

In 29 asymptomatic underweight newborns, 10 true preterms and 19 small-forgestational age (SGA), recordings of respiratory and cardiac rates were performed during the first 72 hours of life. The results may be summarized as follows: 1. Respiratory rates (RR) are slightly elevated during the first day of life. 2. The respiratory-to-cardiac ratio (RR/CR) is very constant throughout the first three days. 3. Low-Apgar infants initially have an elevated RR. 4. True preterm infants have higher cardiac rates (CR) than SGA infants. Not all of the phenomena observed can be totally explained on the basis of existing knowledge.

Adaptation, Physiological↗
PubMed1977

Hybrid cricket auditory behavior: evidence for genetic coupling in animal communication.

Male field crickets produce species-specific and stereotyped calling songs. Conspecific females are attracted to the call. Reciprocal F1 hybrid females prefer the calls of sibling hybrids to reciprocal hybrids. Discrimination is probably based on temporal pattern and not carrier frequency of the call. The results imply that production of song by males and its detection by females have a common genetic basis.

Animal Communication↗
PubMed1977

Seminal quality, spermatozoal outpost, and testicular changes in growing Holstein bulls.

Nine Holstein bulls, initially between the ages of 17 and 22 mo, awaiting proofs in artificial breeding, were ejaculated each summer for 3 yr, and 8 and 7 survivors for 4 and 5 yr, respectively, to study changes in the same group of bulls and determine the predictive value of early measurements. Semen was collected twice a day, 2 days per wk, for 4 wk. Bulls differed in testicular size, consistency, ejaculate volume, total spermatozoal output, percentage of unstained spermatozoa and abnormal spermatozoa, and in several storage and freezing tests. The largest yearly effects were on testis size and consistency, ejaculate volume, and total output of spermatozoa. The latter increased per bull from 28.3 X 10(9) per wk at 17 to 22 mo of age to 40.9 X 10(9) per wk 4 yr later, representing a high output of spermatozoa with a total of only 20 min of intensive sexual preparation per wk. The correlation between testis size and spermatozoal output was .72. Testicular consistency was indicative of semen quality measured simultaneously as judged by correlations with spermatozoal characteristics ranging from .61 to .95. These characteristics are believed to be representative of those Holstein bulls in artificial breeding which are ejaculated frequently.

Animals↗
PubMed1977

The effects of cardiopulmonary bypass with crystalloid and colloid hemodilution on myocardial extravascular water.

The effect of cardiopulmonary bypass (CPB) on myocardial extravascular water (MEW) was evaluated with crystalloid and colloid hemodilution. Heart water was measured gravimetrically and by the double-indicator and thermal methods. CPB without hemodilution resulted in a 5.7 per cent increase in the wet : dry weight ratio of the left ventricle obtained by desiccation to stable weight. CPB with colloid hemodilution to a hematocrit of 10.7 +/- 0.4 per cent resulted in a 5.4 per cent increase in the wet:dry weight ratio. Crystalloid hemodilution to a hematocrit of 9.5 +/- 0.8 per cent resulted in a marked increase in myocardial water with a wet:dry weight ratio 30.3 per cent greater than the controls. Hypothermic (22 degrees C.) crystalloid hemodilution resulted in a 37.4 per cent increase in the wet:dry weight ratio. MEW was also measured by the double-indicator method with Evans blue dye and tritiated water. This method measured 85 per cent of the gravimetrically measured water. Although it indicated the increase in heart water in the crystalloid group, it proved less reliable in the measurement of MEW in this dynamic situation. The thermal heart water was also measured with an impedance and thermistor-bearing catheter similar to that used to measure thermal lung water. This proved ineffective in measuring heart water. Colloid hemodilution was thus found to prevent the development of myocardial edema which occurred with crystalloid hemodilution (p less than 0.01) with and without hypothermia. These findings support the addition of colloid to the hemodilution prime used for cardiopulmonary bypass.

Animals↗