Postbinding insulin resistance around parturition in the isolated rat epitrochlearis muscle

Anti-inflammatory salicylate treatment alters the metabolic adaptations to lactation in dairy cattle

Adapting to the lactating state requires metabolic adjustments in multiple tissues, especially in the dairy cow, which must meet glucose demands that can exceed 5 kg/day in the face of negligible gastrointestinal glucose absorption. These challenges are met through the process of homeorhesis, the alteration of metabolic setpoints to adapt to a shift in physiological state. To investigate the role of inflammation-associated pathways in these homeorhetic adaptations, we treated cows with the nonsteroidal anti-inflammatory drug sodium salicylate (SS) for the first 7 days of lactation. Administration of SS decreased liver TNF-α mRNA and marginally decreased plasma TNF-α concentration, but plasma eicosanoids and liver NF-κB activity were unaltered during treatment. Despite the mild impact on these inflammatory markers, SS clearly altered metabolic function. Plasma glucose concentration was decreased by SS, but this was not explained by a shift in hepatic gluconeogenic gene expression or by altered milk lactose secretion. Insulin concentrations decreased in SS-treated cows on day 7 compared with controls, which was consistent with the decline in plasma glucose concentration. The revised quantitative insulin sensitivity check index (RQUICKI) was then used to assess whether altered insulin sensitivity may have influenced glucose utilization rate with SS. The RQUICKI estimate of insulin sensitivity was significantly elevated by SS on day 7, coincident with the decline in plasma glucose concentration. Salicylate prevented postpartum insulin resistance, likely causing excessive glucose utilization in peripheral tissues and hypoglycemia. These results represent the first evidence that inflammation-associated pathways are involved in homeorhetic adaptations to lactation.

Decreased contraction-stimulated glucose transport in isolated epitrochlearis muscles of pregnant rats

Late pregnancy is characterized by insulin resistance for glucose transport in skeletal muscle. The main purpose of this study was to investigate the effect of late pregnancy on contraction-stimulated glucose transport in isolated rat skeletal muscle after in vitro electrical stimulation. Isolated epitrochlearis muscles of 19-day pregnant and aged-matched nonpregnant control rats were studied. One muscle from each rat was stimulated to contract, and the contralateral muscle served as a resting control. Tension developed during contractile activity, 3-O-methylglucose (3-MG) transport rate, and glycogen concentration were determined. Epitrochlearis muscles from other rats were used to measure insulin-stimulated 3-MG transport. There was no detectable difference between the nonpregnant and pregnant groups for contractile performance (peak tension, total tension, or fatigue). Pregnancy was not associated with significant changes in muscle glycogen concentration (resting or after contractile activity) or the contraction-stimulated decrement in glycogen concentration. For muscles from pregnant vs. nonpregnant groups, there was a 22% reduction (P < or = 0.05) in contraction-stimulated glucose transport, a 28% decrease (P < or = 0.05) in insulin-stimulated glucose transport, and unchanged basal glucose transport. In conclusion, isolated epitrochlearis muscles from pregnant vs. nonpregnant rats had a relative decrement in contraction-stimulated glucose transport that was similar to the relative decline in insulin-stimulated glucose transport. The decrement in contraction-stimulated glucose transport was not attributable to pregnancy-related changes in tension development or glycogen levels. The similar relative decline in insulin- and contraction-stimulated glucose transport raises the possibility that pregnancy impairs a distal process that is common to mechanisms whereby each stimulus activates glucose transport.

Hexokinase II activity and messenger ribonucleic acid abundance in adipose tissue and skeletal muscle during pregnancy and lactation in rats

OBJECTIVE

Our purpose was to investigate the influence of pregnancy and lactation on hexokinase II activity and gene expression in adipose tissue and skeletal muscle of rats.

STUDY DESIGN

Intraabdominal adipose tissue and femoral quadriceps muscle were removed from Sprague-Dawley rats at various times (6 to 10 animals per group) during pregnancy and lactation. Hexokinase II messenger ribonucleic acid was assayed by quantitative ribonuclease protection analysis, and hexokinase activity was measured with the glucose-6-phosphate-coupled assay.

RESULTS

The amount of hexokinase II messenger ribonucleic acid in adipose tissue on day 20 of pregnancy was 55.4% +/- 8.4% (p < 0.01, unpaired Student t test) of the value for nonpregnant control rats; hexokinase II activity was also decreased in this tissue at this time (39.34 +/- 3.05 vs 27.81 +/- 3.61 mU x min(-1) x mg protein(-1), p < 0.05). Hexokinase II activity and messenger ribonucleic acid abundance in skeletal muscle were unaffected by pregnancy and lactation.

CONCLUSION

Both hexokinase II messenger ribonucleic acid abundance and enzyme activity are reduced in adipose tissue of pregnant rats near term, possibly contributing to the insulin resistance associated with late pregnancy.