Biomedical subjects

M R Lebowitz

Publications and source records attributed to M R Lebowitz.

5 recordsLinked to original sources

PubMed1993

The molar ratio of insulin to C-peptide. An aid to the diagnosis of hypoglycemia due to surreptitious (or inadvertent) insulin administration.

After beta-cell stimulation by carbohydrate or other secretagogues, insulin and C-peptide are secreted into the portal vein in a 1:1 molar ratio. A large fraction of endogenous insulin is cleared by the liver, whereas C-peptide, which is cleared primarily by the kidney and has a lower metabolic clearance rate than insulin, traverses the liver with essentially no extraction by hepatocytes. Hence, the molar ratio of insulin to C-peptide in peripheral venous blood (ICPR) should be less than 1.0 during fasting and feeding, unless exogenous insulin is introduced into the systemic circulation. Consequently, an ICPR in excess of 1.0 in a hypoglycemic patient argues persuasively for surreptitious or inadvertent insulin administration and against insulinoma (or sulfonylurea ingestion) as the cause of the hypoglycemia. This conclusion is supported by personal experience and by the literature.

Adult↗

PubMed1992

Effects of atrial natriuretic peptides on metabolism of arginine vasopressin by isolated perfused rat kidney.

Atrial natriuretic peptide (ANP) antagonizes the release and action of arginine vasopressin (AVP) both in vivo and in vitro. We have reported that ANP increases the urinary and metabolic clearances of AVP in normal subjects (A. M. Moses et al. J. Clin. Endocrinol. Metab. 70: 222-229, 1990). To clarify this effect, we perfused isolated rat kidneys in vitro and measured the clearances of AVP for 30 min after the addition of rat ANP [rANP-(1-28), 10(-7) M]. In the perfused kidney, rANP increased the urinary clearance of AVP (UCAVP) from 321 +/- 19 to 417 +/- 20 microliters/min (P less than 0.01) and increased the glomerular filtration rate (GFR) from 558 +/- 28 to 696 +/- 28 microliters/min (P less than 0.01). Fractional excretion of AVP was unchanged. Rates of AVP reabsorption were directly related to filtered AVP, and this relationship was not altered by ANP. ANP did not affect the total organ clearance or the renal metabolic clearance of AVP. The increase in GFR was associated with increases in renal vascular resistance (P less than 0.05), filtration fraction (P less than 0.01), and sodium excretion (P less than 0.001). UCAVP also increased when GFR was raised without ANP by perfusing at higher pressures. The rat ANP clearance receptor agonist [cANP- (4-23), 10(-7) M] did not change GFR or UCAVP. ANP increases UCAVP in the isolated perfused rat kidney. This appears to be a hemodynamic effect of ANP, acting through its biological receptor and not the clearance receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Hypocalcemia.

Explore the source record for details and available documents.

Calcium↗

PubMed1984

The anatomy of a congenitally short limb with clubfoot and ectrodactyly.

Previous studies have shown an association between an abnormal arterial pattern and bony malformations of the human lower limb. We have dissected and performed arteriography on a congenitally short limb with ectrodactyly in order to examine the relationship between arterial pattern and bony anomalies in another type of deformity. The bony anomalies were a combination of short femur, tibia and fibula, clubfoot with tarsal synostoses, metatarsal absence, ectrodactyly, and a bifid hallux. The arterial pattern was characterized by deficiency of the anterior tibial artery and absence of the plantar arch. Major muscular anomalies were noted in the foot only; the muscles of the missing toe were absent and any muscles that normally cross the midventral line were either missing or failed to cross the midline. The superficial peroneal nerve failed to enter the dorsum of the foot and its sensory distribution was assumed by an extra branch of the sural nerve. The most severe abnormalities of the bones, muscles, arteries, and nerves occurred near the midventral line of the foot. We hypothesize that the abnormal arterial pattern put the limb at risk of teratogenic damage by reducing the number of collateral blood supply routes. We suggest that some event, such as extravasation of blood or embolization, compromised the blood flow in the remaining blood vessels and that this event resulted in both a general shortening of the limb and the specific defects observed in the foot. We interpret the anatomy to be consistent with the vascular teratogenic event occurring near the midline of the foot during the fifth week of embryonic development.

Abnormalities, Multiple↗

PubMedDate not supplied

Severe hyperkalemia in two patients with diabetes after cosyntropin administration.

Some patients with diabetes mellitus are at increased risk for the development of hyperkalemia. Included in this group are patients with glucose-induced hyperkalemia who may have renal insufficiency, hyporeninemic hypoaldosteronism, or other impediments to the release or action of aldosterone. In an unusual demonstration of this abnormality, two patients with diabetes, who form the basis of our report, became markedly hyperglycemic and hyperkalemic after cosyntropin administration. To our knowledge, this complication of adrenocorticotropic hormone (ACTH) stimulation testing has not been previously reported. It should therefore be emphasized that the use of cosyntropin as a diagnostic agent can provoke severe hyperglycemia and hyperkalemia in a susceptible subgroup of patients with diabetes mellitus.

Aldosterone↗