Thyroxine-induced hypertrophy of the rabbit heart. Effect on regional oxygen extraction, flow, and oxygen consumption.

Abstract

SUMMARY. The effects of the administration of 0.5 or 1 mg/kg of 1-thyroxine for 3 or 16 days were studied in 55 New Zealand white rabbits. Heart size was 29% above control after 16 days of 1-thyroxine, despite lower body weights. In an anesthetized open-chest animal, regional microspectrophotometric observations of small arteries and veins to determine oxygen extraction were combined with regional blood flow measurements using radioactive microspheres to determine regional oxygen consumption by the Fick principle. Vascular flow reserves were studied through measurement of blood flow after the administration of chromonar HC1, 10 mg/kg. Myocardial oxygen consumption was, respectively, 2.4 and 3.8 times control after 3 and 16 days of 1-thyroxine. This was accompanied by significant increases in both coronary blood flow and oxygen extraction. In control, oxygen extraction and consumption were higher in the subendocardial region compared to the subepicardial area. No significant regional differences were found in flow, oxygen extraction, or consumption after 1-thyroxine administration. Chromonar increased coronary blood flow 2.8 times in the control animals, but did not significantly increase flow or decrease vascular resistance in the rabbits given 1-thyroxine. Adenosine increased coronary blood flow 3.5 times in the control animals but only 2.2 times in animals given 1-thyroxine for 3 days. Animals given 1-thyroxine had hypertrophied hearts with increased oxygen consumption, markedly increased flow, and increased oxygen extraction but without regional left ventricular differences. (Circ Res 52: 272-279, 19S3)

Pilot Studies on the Use of 3,5-Diiodothyropropionic Acid, a Thyroid Hormone Analog, in the Treatment of Congestive Heart Failure

“…The heart rate-mean arterial pressure product is often used as an index of myocardial oxygen consumption [14], and the increase in myocardial oxygen consumption with thyroxine administration has been shown to be proportional to the increase in the heart rate-mean arterial pressure product [15]. Although myocardial oxygen consumption was not measured in the present study, the heart rate-pressure product was not increased by DITPA treatment.…”

Influence of experimental hyperthyroidism on blood and myocardial serotonin in rats

“…Protein and RNA synthesis, coronary blood flow, and oxygen extraction as well as myocardial oxygen consumption are enhanced [12,22]. Furthermore, a hypertrophy of myocytes occurs which is accompanied by a gain in the number of nuclei and mitochondria [21]. The present study was designed to study further the effect of experimental hyperthyroidism on serotonin levels in blood and myocardial tissue of adult rats.…”

Hyperthyroidism increases adenosine transport and metabolism in the rat heart

“…The adaptations that occur lead initially to a greater efficiency in the heart. The rate of protein synthesis is enhanced as is the oxygen consumption [2,5,6]. In addition, there is evidence for alterations in energy metabolism with a reduction in myocardial energy reserve, an enhanced capacity for glycolysis and an increased expression of the Na+-K+ ATPase [3,[7][8][9].…”