An electrogenic sodium pump and baroreceptor function in normotensive and spontaneously hypertensive rats

Postexcitatory depression (PED) and adaptation were examined in slowly adapting aortic baroreceptors of normotensive rats (NTR) and spontaneously hypertensive rats (SHR); an aortic arch-aortic nerve preparation in vitro was used. PED was elicited either mechanically by employing single or double pressure steps, or electrically by antidromic stimulation of the aortic nerve. During PED the axon of the receptor was capable of conducting action potentials and the receptor itself could respond to increased pressures. The relationship between duration of PED and number of impulses preceding it was hyperbolic. In NTR's and SHR's PED was abolished by ouabain or solutions containing no potassium, neither of which affected the steady state pressure-volume relationship of the aorta. These interventions, which are known to block electrogenic pumps, also lowered the pressure threshold and increased the curvature of the steady state pressure-frequency curve. Furthermore, lithium, another agent that blocks electrogenic pumps, also abolished PED. Thus, PED is attributed mainly to an electrogenic sodium pump which operates normally in baroreceptors. We found that adaptation from peak transient to steady state frequency did not appear to be altered significantly when the pump was blocked. Blockage of the pump by ouabain is responsible for the baroreceptor reflex effects elicited by this drug. We conclude that resetting and reduced sensitivity in SHR baroreceptors are not attributed to significant differences in electrogenic pump activity.     

Usefulness of serial carcinoembryonic antigen (CEA) determinations in monitoring chemotherapy

Serial carcinoembryonic antigen (CEA) levels were measured during chemotherapy for metastatic cancer in 94 patients. Criteria for chemotherapy responses were those used by the Central Oncology Group. Patients were classified according to changes in CEA levels and response to chemotherapy. Four categories represented a positive correlation: (1) increasing abnormal CEA with progressing disease, (2) decreasing abnormal CEA with disease regression, (3) unchanged abnormal CEA with stable disease, (4) change from normal to abnormal CEA with progressive disease. Positive correlation of serial CEA levels with clinical responses occurred in 71% of patients with GI cancer, 51% with breast cancer, 42% with sarcoma, 50% with respiratory cancer, and 25% with melanoma. These data indicate that serial CEA determinations may be of value as an additional parameter of response to chemotherapy in gastrointestinal cancer.     

Electrophysiological responses of cardiac muscle to isoproterenol covalently linked to glass beads

We investigated the effects of isoproterenol aryl glass beads on the electrical properties of cardiac muscle and related these to our previous results concerning biochemical and contractile effects (Ingebretsen et al., Circ, Rs., 40: 474-484, 1977). Beads (10-15) were placed near one end to guinea pig papillary muscles mounted horizontally in a bath perfused with Krebs-Henseleit solution at 30 degrees C and stimulated at 0.2 Hz. The beads produced increased tension and elevation and slight lengthening of the plateau potential when [k+]o = 3.8 mM. After depolarization to a resting potential of -49 mV with [K+]o = 22 mM, isoproterenol beads restored contraction to a comparable extent as occurred with 10(-8) M soluble drug. During field stimulation, action potentials were initiated at the site of bead application and spread decrementally. When beads were placed distal to the site of point stimulation, virtually no excitation could be obtained from cells in the vicinity of the beads. When they were placed close to the stimulating electrode, the beads increased excitability and typical slow action potentials spread to the other end of the muscle. These potentials had the characteristics associated with the slow inward Ca2+ current. The slow channel blocker, D-600, blocked responses to isoproterenol beads. Tetrodotoxin caused responses similar to those obtained with K+ depolarization. The beads probably act by stimulating only a small fraction of the papillary muscle catecholamine receptors. Spread of action potentials from these sites and propagated tension depend on Ca2+ influx, but the nature of an intermediate messenger involved in the propagation of contractions is unknown.     

Quantitative analysis of the plain radiographic appearance of unicameral bone cysts

The reliability and frequency specificity of the 80-Hz amplitude-modulation-following response (80-Hz AMFR) during sleep detected by phase coherence as a measure of the hearing threshold was evaluated in 169 affected ears of 125 children with hearing impairment. The 80-Hz AMFR at a carrier frequency of 1000 Hz was monitored in all 169 ears and the auditory brainstem response (ABR) elicited by 1000-Hz tone pips was evaluated in 93 ears. Both responses were examined during sleep, and the thresholds were compared with the behavioral hearing threshold, which was determined by standard pure-tone audiometry or play audiometry. In 24 ears of 22 children with various patterns of audiogram, the 80-Hz AMFR was examined at different carrier frequencies, and the threshold pattern was compared with the pure-tone audiogram to investigate the frequency specificity of 80-Hz AMFR. The mean and standard deviation of the difference between the 80-Hz AMFR at a carrier frequency of 1000 Hz and pure-tone thresholds of 1000 Hz was 3.8 and 12.9 dB, and that between the ABR and pure-tone thresholds was 6.8 and 14.1 dB, respectively. The threshold patterns of 80-Hz AMFR clearly followed the corresponding audiogram patterns in all types of hearing impairment. The measurement of 80-Hz AMFR thus appears to be accurate in hearing assessment and to have good frequency specificity in children during sleep.