QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Motil, K. J. Articles by Garza, C. Search for Related Content PubMed PubMed Citation Articles by Motil, K. J. Articles by Garza, C.

Insulin, Cortisol and Thyroid Hormones Modulate Maternal Protein Status and Milk Production and Composition in Humans^{1, 2,}

USDA/ARS Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, and Texas Children's Hospital, Houston, TX 77030

The partitioning of dietary and endogenous nutrients during lactation is not well understood. To examine associations between plasma hormone and substrate profiles and indices of either maternal body protein metabolism or lactational performance, we measured plasma insulin, cortisol, prolactin, thyroxine, triiodothyronine, individual amino acid, blood urea nitrogen, and prealbumin concentrations in lactating and nulliparous women in the postabsorptive state. We related these measurements to the subjects' nitrogen balance, urinary 3-methylhistidine excretion, [1-¹³C]leucine metabolism and milk production. Insulin concentrations showed significant positive relationships with nitrogen balance and prealbumin concentrations; cortisol levels showed a significant negative relationship with nitrogen balance and a significant positive relationship with leucine incorporation into protein. Thyroid hormone concentrations showed significant positive relationships with urinary 3-methylhistidine excretion, leucine incorporation into protein, and milk production. Proline concentrations were associated positively with nitrogen balance and negatively with leucine incorporation into protein, whereas glutamate-glutamine concentrations showed positive associations with leucine oxidation and milk nitrogen concentrations. We propose that insulin and cortisol modulate the channeling of nutrients between anabolic and anti-anabolic aspects of maternal body protein metabolism, whereas thyroid hormones and cortisol modulate nutrient partitioning toward milk production and visceral protein synthesis. We suggest that some nonessential amino acids (proline, glutamate-glutamine) may become limiting during lactation because of their unique contributions to milk protein synthesis.

KEY WORDS: • lactation • insulin • cortisol • humans • protein metabolism

¹ This work is a publication of the USDA/ARS Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX. This project has been supported in part by NIH grants 5R01-HD-21049-02-05 and RR00188-25, National Institute of Arthritis, Diabetes, and Digestive and Kidney Diseases grant AM-28129, and has been funded in part with federal funds from the U.S. Department of Agriculture, Agricultural Research Service under Cooperative Agreement no. 58-6250-1-003. The contents of this publication do not necessarily reflect the views or policies of the U.S. Department of Agriculture, nor does mention of trade names, commercial products or organizations imply endorsement from the United States government.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ To whom correspondence and reprint requests should be addressed.

⁴ Current address: Department of Range Science, Texas A&M University, College Station, TX 77843.

⁵ Current address: Division of Nutritional Sciences, 127 Savage Hall, Cornell University, Ithaca, NY 14853.

Manuscript received 17 December 1993. Revision accepted 28 February 1994.