Physiological hyperinsulinemia stimulates p70(S6k) phosphorylation in human skeletal muscle

Using tracer methods, insulin stimulates muscle protein synthesis in vitro, an effect not seen in vivo with physiological insulin concentrations in adult animals or humans. To examine the action of physiological hyperinsulinemia on protein synthesis using a tracer-independent method in vivo and identify possible explanations for this discrepancy, we measured the phosphorylation of ribosomal protein S6 kinase (P70(S6k)) and eIF4E-binding protein (eIF4E-BP1), two key proteins that regulate messenger ribonucleic acid translation and protein synthesis. Postabsorptive healthy adults received either a 2-h insulin infusion (1 mU/min.kg; euglycemic insulin clamp; n = 6) or a 2-h saline infusion (n = 5). Vastus lateralis muscle was biopsied at baseline and at the end of the infusion period. Phosphorylation of P70(S6k) and eIF4E-BP1 was quantified on Western blots after SDS-PAGE. Physiological increments in plasma insulin (42 +/- 13 to 366 +/- 36 pmol/L; P: = 0.0002) significantly increased p70(S6k) (P: < 0.01), but did not affect eIF4E-BP1 phosphorylation in muscle. Plasma insulin declined slightly during saline infusion (P: = 0.04), and there was no change in the phosphorylation of either p70(S6k) or eIF4E-BP1. These findings indicate an important role of physiological hyperinsulinemia in the regulation of p70(S6k) in human muscle. This finding is consistent with a potential role for insulin in regulating the synthesis of that subset of proteins involved in ribosomal function. The failure to enhance the phosphorylation of eIF4E-BP1 may in part explain the lack of a stimulatory effect of physiological hyperinsulinemia on bulk protein synthesis in skeletal muscle in vivo.

Breastfeeding outcomes of women following uncomplicated birth in Hamilton-Wentworth

OBJECTIVE

To examine infant feeding practices up to 8 weeks postpartum in Hamilton-Wentworth.

METHODS

A cross-sectional survey of 227 women using a pre-discharge, self-administered questionnaire, medical record review and follow-up telephone interview.

RESULTS

Breastfeeding initiation rate was 85%. By 6-8 weeks postpartum, 30% of women had stopped breastfeeding; 55% had switched to formula within the first 14 days. Infants who did not receive supplementation in hospital were 2.49 times more likely than infants who received supplementation to breastfeed for at least 6 weeks. Although 54% of mothers who initiated breastfeeding reported receiving formula gift packs, no association was found.

CONCLUSIONS

The breastfeeding initiation rate appears to have increased in Hamilton-Wentworth since 1995. However, this study reinforces the need to address early cessation and infant supplementation, and raises concern about violation of the WHO/UNICEF International Code of Marketing of Breastmilk Substitutes through mailing of formula coupons.

Breastfeeding outcomes of women following uncomplicated birth in Hamilton-Wentworth

OBJECTIVE

To examine infant feeding practices up to 8 weeks postpartum in Hamilton-Wentworth.

METHODS

A cross-sectional survey of 227 women using a pre-discharge, self-administered questionnaire, medical record review and follow-up telephone interview.

RESULTS

Breastfeeding initiation rate was 85%. By 6-8 weeks postpartum, 30% of women had stopped breastfeeding; 55% had switched to formula within the first 14 days. Infants who did not receive supplementation in hospital were 2.49 times more likely than infants who received supplementation to breastfeed for at least 6 weeks. Although 54% of mothers who initiated breastfeeding reported receiving formula gift packs, no association was found.

CONCLUSIONS

The breastfeeding initiation rate appears to have increased in Hamilton-Wentworth since 1995. However, this study reinforces the need to address early cessation and infant supplementation, and raises concern about violation of the WHO/UNICEF International Code of Marketing of Breastmilk Substitutes through mailing of formula coupons.