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Rat Placental Protein Synthesis and Peptide Hormone Secretion in Relation to Malnutrition from Protein Deficiency or Alcohol Administration

Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

Placental composition and function were examined in rats receiving a diet low in protein or consuming alcohol along with normal protein intakes. Placentas were obtained from rats fed 18% lactalbumin (control group), 5% lactalbumin (low-protein-fed group), or 18% lactalbumin with 20% alcohol in the drinking water (alcohol-fed group) during the last 14 days of pregnancy. The amounts of RNA and of protein in the placentas on day 20 of pregnancy were significantly reduced in both the low-protein-fed and the alcohol-fed groups. Membrane-bound and free ribosomes were isolated from the placentas of each dietary group. For each class of ribosome, the amount per placenta, the proportion of polyribosomes and their in vitro capacity for protein synthesis were measured. The total amounts of both free and membrane-bound ribosomes were reduced in placentas from the low-protein and alcohol groups. In addition, the low-protein group showed a lower percentage of ribosomes as polysomes and a reduced capacity per ribosome to incorporate amino acids into peptide chains in vitro. Rat chorionic mammotropin (rCM), a peptide hormone secreted by the placenta, was measured by radio-receptor assay in serum and in placental extracts obtained from the three experimental groups. The concentration of rCM in serum and placental extracts was much lower in the low-protein-fed and alcohol-fed groups than in the control group. The reduction in placental rCM was proportional to the reduced amount of ribosomal RNA in the placenta. These data demonstrate that a major effect of both protein deficiency and ethanol consumption is a reduction in placental protein synthesis, including the output of rCM, as a result of fewer ribosomes. The consequently reduced action of this hormone may result in inadequate maternal supplies of nutrients to the fetus, thus contributing to reduced fetal growth by the end of gestation.

KEY WORDS: • placenta • placental lactogen • protein deficiency • alcohol

¹ Present address: Department of Nutrition, Rutgers University, New Brunswick, New Jersey.

² Present address: Department of Pediatrics, University of Southern Alabama Medical Center, Mobile, Alobama.

Manuscript received 1 December 1978.