Insulin Responsiveness of Neonatal Pig Myocardium

Abstract

The transition from preferential use of carbohydrates to fatty acids for energy production by neonatal mammalian myocardium might be hormonally influenced. In neonatal pigs (between 1 and 4 days of age), plasma glucose, lactate, and glucagon concentrations remained constant at adult levels, while plasma triglycerides and insulin content remained stable at substantially lower levels. Insulin, whether administered in vivo or during perfusion, increased myocardial glucose utilization [GU] and lactate production [LP]. Stimulation of GU and LP by insulin exposure in vivo persisted for at least 1 h during perfusions after insulin was removed. Exogenous lactate (0.5 mM) diminished insulin-stimulated GU and LP; and was used as a substrate at 1.25mM. Thus, insulin augmented glycolytic activity of neonatal piglet myocardium; however, exogenous lactate, within the physiological range, altered the nature of the myocardium’s response by, as yet, undetermined mechanisms. Therefore, the transition from carbohydrate to fatty acid utilization for energy production by the neonatal myocardium does not appear to result from decreased carbohydrate metabolism or reduced myocardial responsiveness to insulin.

Insulin Reduces Basal Release of Atrial Natriuretic Factor by Isolated, Perfused Neonatal Pig Hearts

“…Myocardial metabolic activity was sub stantial (table 1) and slightly exceeded rates of glucose utilization and lactate production pre viously reported [18], These data indicate that the hearts used in this study were physiologi cally intact, displaying reasonably characteris tic metabolic activity and insulin responsive ness […”

“…Based on our data of plasma insulin levels in 1-to 4-day-old pig lets [ 18], this insulin concentration is supraphysiological; nevertheless, it lies within the range that we have shown produces maximal stimulation o f carbohydrate metabolism in isolated perfused neonatal pig hearts [18]. Since we have observed no change in plasma insulin level between 1 and 4 days postpartum in neo natal pigs [18], the same insulin concentration was used for all perfusions.…”

“…Flow rates and metabolic parameters (Oj consump tion, glucose utilization, and lactate production) were determined as previously described [17,18]. Reagents used for these assays were purchased from Sigma.…”

“…However, the ability of insulin to affect ANF release has yet to be demonstrated. In the present study, an in vitro system that has been extensively used by this laboratory to investigate hormon al influences on developmental changes in myocardial metabolism [17,18] was exploited to examine the effect o f insulin on ANF release by isolated, neonatal pig hearts per fused under constant pacing and with mini mal change in atrial pressure.…”