Biomedical subjects

J R Tobin

Publications and source records attributed to J R Tobin.

At least 55 records · Page 3Linked to original sources

PubMed1992

Muscarinic cholinergic receptors in canine adrenal gland.

Muscarinic cholinergic receptor stimulation has been reported to modulate adrenal catecholamine and steroid secretion and influence medullary vascular tone. The present study was undertaken to localize and characterize muscarinic cholinergic receptor binding sites in canine adrenal medulla and cortex. Binding studies using semipurified membranes demonstrated specific, saturable binding of L-[benzilic-4,4'-3H(N)]-quinuclidinyl benzilate ([3H]QNB) in medulla, with a dissociation constant (KD) equal to 152 pM and estimated maximal binding sites (Bmax) equal to 179 fmol/mg protein. Displacement of [3H]QNB by cholinergic agents in order of decreasing potency was atropine, pirenzepine, oxotremorine, pilocarpine, and carbamylcholine, suggesting the receptor was M1 subtype, similar to sympathetic ganglion muscarinic receptors. Autoradiographic imaging studies demonstrated highly specific, homogeneous binding throughout the medulla. No specific binding was found in adrenal cortex. These results suggest that muscarinic effects on blood flow may be neurally mediated, rather than the result of stimulation of vascular muscarinic receptors. In medulla, muscarinic receptors are evenly distributed and modulate catecholamine secretion in all cells rather than subpopulations of cells as in other species. Absence of [3H]QNB binding in cortex argues against muscarinic receptor modulation of cortical steroid secretion.

Adrenal Cortex↗

PubMed1991

Astemizole-induced cardiac conduction disturbances in a child.

The newly available antihistamine astemizole (Hismanal) has been previously associated with hemodynamically significant cardiac tachydysrhythmias. We describe a 3-year-old girl who developed multiple different cardiac dysrhythmias after an astemizole overdose. No hemodynamic compromise occurred, and the electrocardiogram returned to normal without use of antiarrhythmic agents within 7 hours.

Arrhythmias, Cardiac↗

PubMed1991

Effect of adrenal hypotension on elicited secretory activity in anesthetized dogs.

The objective of this study was to determine whether three- to fourfold increases in adrenal medullary blood flow (MQ), observed during catecholamine secretion induced by splanchnic nerve stimulation (NS), are necessary for a maximal secretory response. Eight pentobarbital-anesthetized adult male mongrel dogs (25-35 kg) were subjected to two episodes of NS-induced catecholamine secretion. To limit increases in MQ, one NS (20 Hz, 8 V, 1.5 ms) was performed under control conditions, the other was after reduction of adrenal perfusion pressure (PP). PP was 124.8 +/- 6.0 at control and was reduced to 23.0 +/- 1.0 mmHg by inflation of an aortic occluder located 3 in. above the adrenals. NS under control conditions increased ipsilateral MQ (measured using radiolabeled microspheres) from 181 +/- 39 to 1,336 +/- 199 ml.min-1.100 g-1 and adrenal epinephrine secretion from 184 +/- 128 to 11,445 +/- 5,216 ng.min-1.g medulla-1. Contralateral MQ and cortical blood flow were unaffected by NS. Reduction of PP decreased MQ to 32 +/- 6 ml.min-1.100 g-1 and adrenal cortical blood flow from 251 +/- 23 to 25 +/- 6 ml.min-1.100 g-1.PP reduction had no effect on either corticosteroid secretion or unstimulated epinephrine secretion. NS at reduced PP increased ipsilateral MQ to 146 +/- 27 ml.min-1.100 g-1 and epinephrine secretion to 13,935 +/- 5,175 ng.min-1.g medulla-1. These data indicate that epinephrine secretion is not altered when MQ is limited by reduction of PP and suggest that, at normal PP, increases in MQ during catecholamine secretion are not necessary for a maximal secretory response.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex Hormones↗

PubMed1991

Cholinergic regulation of adrenal medullary blood flow.

To determine the relative role of nicotinic and muscarinic mechanisms in splanchnic nerve stimulation (NS)-induced adrenal catecholamine secretion and medullary vasodilation, 12 pentobarbital-anesthetized dogs were subjected to three identical stimulations. The first NS was performed before drug administration and served as a control. The second NS was performed after administration of either the muscarinic antagonist, atropine 0.5 mg/kg (group 1), or the nicotinic antagonist, hexamethonium 20 mg/kg (group 2). The third NS was performed after administration of both drugs. NS in the absence of drug resulted in 4-fold and greater than 200-fold increases in medullary blood flow (Q, measured with radiolabeled microspheres) and catecholamine secretion (assayed by high-pressure liquid chromatography), respectively. Atropine, when administered alone (group 1), had no effect on these responses. Subsequent administration of hexamethonium to group 1 animals resulted in complete blockade of NS-induced changes in medullary Q and secretion. Hexamethonium alone (group 2) reduced the catecholamine response to NS by 95% but had no effect on the medullary Q response. Addition of atropine further attenuated the increase in catecholamine secretion induced by NS and completely blocked the medullary Q increase. These data suggest the presence of redundant mechanisms to increase medullary Q during NS. One mechanism likely involves neurally released acetylcholine-stimulating vascular muscarinic receptors, whereas the second requires either chromaffin cell degranulation or nicotinic ganglionic transmission.

Adrenal Medulla↗

PubMed1990

Changes in adrenal oxygen consumption during catecholamine secretion in anesthetized dogs.

Prior attempts to study adrenal medullary O2 metabolism during catecholamine secretion have been unsuccessful because venous blood from medulla mixes with venous blood from the much larger cortex. To circumvent this problem, eight adult mongrel dogs were pretreated for 5-6 wk with the adrenocorticolytic agent 1,1-dichloro-2-(o-chlorophenyl)-2-(p-chlorophenyl)ethane (o,p'-DDD). Prednisolone (5 mg/day) and fludrocortisone (0.1 mg.10 kg-1.day-1) were administered orally to prevent adrenocortical insufficiency. Animals were then anesthetized with pentobarbital sodium and subjected to splanchnic nerve stimulation (NS) at 20 and 4 Hz to elicit catecholamine secretion. NS at 20 Hz increased epinephrine secretion from 1.6 +/- 0.7 to 1,780 +/- 762 ng.min-1.g medulla-1 but had no effect on medullary O2 consumption. Medullary blood flow (MQ) increased from 216 +/- 63 to 1,522 +/- 182 ml.min-1.100 g-1, and O2 extraction decreased from 2.7 +/- 0.7 to 0.8 +/- 0.2%. NS at 4 Hz increased epinephrine secretion from 3.1 +/- 1.4 to 76 +/- 17 ng.min-1.g medulla-1 and MQ from 226 +/- 66 to 649 +/- 122 ml.min-1.100 g-1 but had no effect on adrenal O2 consumption or extraction. Cortical blood flow was 342 +/- 98 ml.min-1.100 g-1 at baseline and was unaffected by NS. Gross weight of cortex was reduced by 80% in o,p'-DDD-treated animals, and histological examination of glands from three animals showed only rare islands of glomerulosa cells remaining. These data suggest that increases in MQ during NS do not occur in response to changes in O2 consumption.

Adrenal Glands↗

PubMed1986

Prolonged mechanical ventilation of infants after open heart surgery.

Records of 140 infants younger than 2 yr of age who had undergone open heart surgery were studied to evaluate the duration of postoperative mechanical ventilation (MV), to determine the relationship between prolonged MV and mortality, and to identify variables predisposing the patient to prolonged MV. MV was required beyond the first postoperative day in 56 infants, and was prolonged for at least 7 days in 19 infants. Mortality was approximately the same (16% to 17%) whether or not MV was required for more than 7 days. Preoperative and intraoperative variables associated with longer MV included younger age, longer cardiopulmonary bypass time, longer aortic cross-clamp time, and preoperative MV. Multiple predisposing factors increased the probability of prolonged MV. Postoperative variables including premature extubation and a second surgical procedure also were associated with prolonged MV. The consequences of prolonged MV may be minimized by early nutritional support, aggressive surveillance for treatable complications, and avoidance of premature extubation.

Cardiac Surgical Procedures↗

PubMed1984

Effect of three-year and four-year curricula on physicians' attitudes and medical practice.

The purpose of the study reported here was to identify the differences, if any, between graduates who were in different curricula at Loyola University of Chicago Stritch School of Medicine. Physicians from the four-year curriculum plan indicated they believed they were more adequately taught than those in the subsequent three-year curriculum plan. The training that the former physicians received seemed to provide them with a better basis for being independent. They regarded as desirable a medical practice requiring them to deal with many uncertainties in diagnosis and therapy. Physicians graduating from the medical school when the three-year plan was in effect seemed to have more personal and academic problems, and more of them suggested that various subjects should have been given greater emphasis in the medical school curriculum.

Attitude of Health Personnel↗

PubMed1981