Cerebrospinal fluid retrieval in the conscious dog: a methods development study.

A chronic cerebrospinal fluid access system is described for use in the conscious sling-restrained dog. In a pilot study of ten dogs, a fenestrated barium-impregnated silastic catheter was surgically implanted in the subarachnoid space of the second cervical vertebra through a dorsal laminectomy. This fenestrated catheter was coupled to a subcutaneous access port. Following surgery, cerebrospinal fluid was sampled weekly and evaluated for protein content and cytology. The cerebrospinal fluid albumin to serum albumin ratio was calculated for each sample to evaluate blood-brain barrier integrity. The instrumentation was successfully implanted in five of the first eight dogs using a midbody dorsal laminectomy. Cerebrospinal fluid access was maintained in these dogs for 21 +/- 10 days. Using a slight modification of the original technique, the final two dogs were instrumented through a caudodorsal laminectomy of the second cervical vertebra. The cerebrospinal fluid access system remains patent after 444 days of study in these two dogs. Necropsy evaluation suggested that catheter failure in the immediate postoperative period was due to gross malposition of the catheter. Chronic catheter failure occurred secondary to obstruction by local fibrous tissue reaction. Using this instrumentation, a pharmacokinetic evaluation of the plasma and cerebrospinal fluid deposition of an intravenous bolus of acyclovir was successfully performed twice in a single dog without complications. This instrumentation could provide chronic cerebrospinal fluid access for multiple pharmacokinetic studies in the conscious dog.

Electrocardiographic effects of experimental myocardial infarction in pigs.

Myocardial infarctions were produced in young domestic farm pigs by ligating coronary arteries. Arteries ligated in four groups were (A) left anterior descending, (B) branches of left anterior descending, (C) left circumflex, and (D) right coronary artery. After 7 or 8 days, the hearts were removed and dissected and the infarcted areas measured. Vectorcardiograms were taken before ligation and just before termination. High recording speeds and sensitivities were used so that details of the QRS complexes could be seen. Difference vectors were computed as a function of time during QRS. In groups A and B, statistically significant differences in QRS components before and after ligation were found. Also, there were statistically significant correlations between vectorcardiographic deflections and the ratio of infarct weight to heart weight. The changes were related to known excitation patterns of the pig heart.

Insulin infusion therapy. Potential benefits and risks.

A mass of evidence favors the concept of euglycemic management of insulin-dependent diabetes, despite significant potential complications. Patients with advanced nephropathy and/or autonomic neuropathy are very poor risks, and infusion therapy does not reverse well-established complications. To well-motivated, educated patients, infusion therapy offers the conveniences of more flexible timing of meals and of having a premeal bolus infusion rather than a premeal injection. With improvement in the technology of continuous glucose monitoring and closed-loop systems, as well as basic improvements in immunologic techniques for islet transplantation, the future may offer a choice of excellent euglycemic therapies for insulin-dependent diabetes. Meanwhile, infusion therapy, which was once only a research tool, is now widely available and is appropriate for near-euglycemic management of diabetes in selected patients.

Glucagon administration decreases hepatic nuclear triiodothyronine binding capacity.

The maximal binding capacity (MBC) of nuclear triiodothyronine (T3) receptor sites in rat liver decreases markedly after glucagon administration. Administration of serial doses of glucagon (2.5 microgram/100 g BW) resulted in a 33% decrease in MBC in 3.5 h and MBC was reduced by 45% in 6.25 h. The individual doses used were in the same order of magnitude as those used in the treatment of hypoglycemic human subjects (1.5 microgram/100 g BW). This report presents the first evidence that a peptide hormone can change the number of nuclear T3 receptor sites. The physiological significance of these findings remains to be clarified.

The difference vector: assessment of effects of changes or interventions.

Vector dipole moments were measured on young pigs before and one week after ligation of the left anterior descending coronary artery. Vectors were obtained for the three peaks of vector spatial magnitude, M. Preoperative, postoperative, and difference vectors were measured for each peak. If excitation is normal except through the infarcted tissue, the difference vector should be more closely related to the infarct because the normal excitation cancels out. It was found that the postoperative vector was changed by the infarct but that the difference vector was a better indication of infarction. This paper was designed to introduce the method using experimental data for a small number of pigs.