Brain serotonergic activity and plasma amino acid levels in genetically obese Zucker rats

Free lysine, methionine, threonine, and tryptophan were determined in small samples of blood obtained by finger punch from human subjects. The levels of the four amino acids rose rapidly after the subjects consumed protein as baked halibut; the extent and duration of the increases were roughly proportional to the amount of protein eaten and to the amino acid composition of the protein. The increases of free methionine and threonine in plasma were somewhat less when butter was taken with fish but starch (as potato) or sucrose did not affect the values. Other foods tested at the 19.0-g level of protein included egg, a commercial breakfast cereal, and the same cereal plus milk. In general the increase or decrease of each amino acid tested was related to the amount of that amino acid in the test food. The plasma amino acid (PAA) ratio of Longenecker and Hause was calculated for each food and was useful in evaluating the increase or decrease of each specific amino acid. The present work appears to offer a practical procedure for studying the plasma amino acid response of groups of human subjects to variations in dietary protein.

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Adenohypophyseal response to hypophysiotropic hormones in male obese Zucker rats

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1985.249.4.e380 ◽

1985 ◽

Vol 249 (4) ◽

pp. E380-E384

Author(s):

M. L. Heiman ◽

J. R. Porter ◽

M. V. Nekola ◽

W. A. Murphy ◽

A. D. Hartman ◽

...

Keyword(s):

Growth Hormone ◽

Amino Acid ◽

Luteinizing Hormone ◽

Zucker Rats ◽

Pituitary Cells ◽

Response Curves ◽

Amino Acid Molecule ◽

Obese Zucker Rat ◽

Recessive Homozygote ◽

Obese Zucker Rats

Description of the recessive, homozygote obese Zucker rat (fafa) includes disorders of growth and reproduction. The aim of this study was to compare responsiveness of adenohypophyseal cells, obtained from male fafa rats and from their lean siblings, to growth hormone-releasing factor (GRF) and to luteinizing hormone-releasing hormone (LHRH). Pituitary cells were cultured for 4 days and were then challenged with either GRF-29 (the NH2-terminal 29 amino acid GRF peptide that expresses full biological activity of its parent 44 amino acid molecule) or [D-Trp6]LHRH (LHRH-A, an LHRH agonist). Medium was assayed for growth hormone (GH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) by radioimmunoassay. Dose-response curves were compared using the computer program ALLFIT. The median effective GRF-29 concentration (EC50) computed for hypophyseal cells cultured from lean animals (0.30 +/- 0.01 fM; means +/- SE of 4 experiments) was less (P less than 0.01) than that calculated for cells obtained from fafa rats (15.8 +/- 6.7 fM). In contrast, cells derived from lean littermates required a larger (EC50) concentration of LHRH-A than did gonadotrophs cultured from obese rats [58.2 +/- 1.2 vs. 10.7 +/- 1.2 pM (P less than 0.01) and 59.4 +/- 10.4 vs. 15.7 +/- 7.6 pM (P less than 0.05)] to secrete LH and FSH, respectively. Our data describe an attenuated pituitary response to GRF-29 and an enhanced response to LHRH-A in the fafa.

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